Preface

Table of contents

Introduction

Overview

Python

Python is probably the language that is most like Pike. Pike is faster and has better object orientation. It also has a syntax similar to C++, which makes it more familiar for people who know C++. Python on the other hand, has a lot more libraries available.

C++

Pike's syntax is almost the same as for C++. A huge difference is that Pike is interpreted. This makes the code slower, but reduces compile times to almost nothing. For those few applications which require the speed of C or C++, it is often easier to write a Pike extension than to write the whole thing in C or C++.

Lisp and Scheme

Internally Pike has a lot in common with Lisp and Scheme. They are both stack based, byte-compiled, interpreted languages. Pike is also a 'one-cell' language, just like Scheme.

Pascal

Pike has nothing in common with Pascal.

Tcl/Tk

Pike is similar to Tcl/Tk in intent and they both have good string handling. Pike has better data types and is much faster however. On the other hand Tcl/Tk has X windows system support.

What is Pike

• A programming language
• Object oriented
• Interpreted
• Fast
• Dynamic
• High-level
• similar to C++
• easy to extend
• (a fish)

• Garbage collection
• Advanced string functions
• 5 years of development behind it
• Advanced data types such as associative arrays
• Support for bignums
• Builtin socket support

How to read this manual

italics

Italics is used as a placeholder for other things. If it says a word in the text it means that you should put your own word there.

bold

Bold is just used to emphasize that this word is not merely what it sounds like. It is actually a term.

fixed size

Fixed size is used to for examples and text directly from the computer.

Chapter 1, Getting started

int main()
{
    write("hello world\n");
    return 0;
}

	$ pike hello_world.pike
	hello world
	$ 

int main()

{
    write("hello world\n");
    return 0;
}

write("hello world\n");

return 0;

#!/usr/local/bin/pike

int main()
{
    write("hello world\n");
    return 0;
}

	$ chmod +x hello_world.pike
	$ ./hello_world.pike
	hello world
	$ 

#!/usr/local/bin/pike

int main(int argc, string *argv)
{
    if(argc > 1 && argv[1]=="--traditional")
    {
        write("hello world\n"); // old style
    }else{
        write("Hello world!\n"); // new style
    }
    return 0;
}

	$ chmod +x hello_world.pike
	$ ./hello_world.pike
	Hello world!
	$ ./hello_world.pike --traditional
	hello world
	$ 

int main(int argc, string *argv)

The arguments to main are taken from the command line when the Pike program is executed. The first argument, argc, is how many words were written on the command line (including the command itself) and argv is an array formed by these words.

    if(argc > 1 && argv[1] == "--traditional")
    {
        write("hello world\n"); // old style
    }else{
        write("Hello world!\n"); // new style
    }

argc > 1 && argv[1] == "--traditional"

Also note the comments:

        write("hello world\n"); // old style

We have already seen an example of the if statement:

if( expression )
     statement1;
else
     statement2;

if( expression )
    statement1;

Note for beginners: go back to our first example and make sure you understand what if does.

Another very simple control structure is the while statement:

while( expression )
    statement;

modifiers type name(type name1, type name2, ...)
{
    statements
}

Int

The integer type stores an integer.

Float

This variable type stores a floating point number.

Array

Arrays are basically a place to store a number of other values. Arrays in Pike are allocated blocks of values. They are dynamically allocated and do not need to be declared as in C. The values in the array can be set when creating the array like this:

arr=({1,2,3});

Or, if you have already created an array, you can change the values in the array like this:

This sets entry number ind in the array arr to data. ind must be an integer. The first index of an array is 0 (zero). A negative index will count from the end of the array rather than from the beginning, -1 being the last element. To declare that a variable is an array we simply type array in front of the variable name we want:

array i;

We can also declare several array variables on the same line:

string i, j;

If we want to specify that the variable should hold an array of strings, we would write:

array (string) i;

String

A string contains a sequence of characters, a text, i.e. a word, a sentence or a book. Note that this is not simply the letters A to Z; special characters, null characters, newlines and so on can all be stored in a string. Any 8-bit character is allowed. String is a basic type in Pike, it is not an array of char like it is in C. This means that you cannot assign new values to individual characters in a string. Also, all strings are "shared", i.e. if the same string is used in several places, it will be stored in memory only once. When writing a string in a program, you enclose it in double quotes. To write special characters you need to use the following syntax:

\n	newline
\r	carriage return
\t	tab
\b	backspace
\"	" (quotation character)
\\	\ (literal backslash)

Mapping

A mapping is basically an array that can be indexed on any type, not just integers. It can also be seen as a way of linking data (usually strings) together. It consists of a lot of index-data pairs which are linked together in such a way that map[index1] returns data1. A mapping can be created in a way similar to arrays:

map=([five:good, ten:excellent]);

You can also set that data by writing map[five]=good. If you try to set an index in a mapping that isn't already present in the mapping it will be added as well.

Multiset

A multiset is basically a mapping without data values. When referring to an index in the multiset a 1 (one) will be returned if the index is present and 0 (zero) otherwise.

Chapter 2, A more elaborate example

#!/usr/local/bin/pike

mapping (string:array(string)) records =
([
    "Star Wars Trilogy" : ({
        "Fox Fanfare",
        "Main Title",
        "Princess Leia's Theme",
        "Here They Come",
        "The Asteroid Field",
        "Yoda's Theme",
        "The Imperial March",
        "Parade of the Ewoks",
        "Luke and Leia",
        "Fight with Tie Fighters",
        "Jabba the Hut",
        "Darth Vader's Death",
        "The Forest Battle",
        "Finale"
    })
]);

void list_records()
{
    int i;
    array (string) record_names=sort(indices(records));

    write("Records:\n");
    for(i=0;i<sizeof(record_names);i++)
        write(sprintf("%3d: %s\n", i+1, record_names[i]));
}

void show_record(int num)
{
    int i;
    array (string) record_names = sort(indices (records));
    string name=record_names[num-1];
    array (string) songs=records[name];
    
    write(sprintf("Record %d, %s\n",num,name));
    for(i=0;i<sizeof(songs);i++)
        write(sprintf("%3d: %s\n", i+1, songs[i]));
}

int main(int argc, array (string) argv)
{
    if(argc <= 1)
    {
        list_records();
    } else {
        show_record((int) argv[1]);
    }
}

2.1 Taking care of input

void add_record()
{
    string record_name=readline("Record name: ");
    records[record_name]=({});
    write("Input song names, one per line. End with '.' on its own line.\n");
    while(1)
    {
        string song;
        song=readline(sprintf("Song %2d: ",
                                                    sizeof(records[record_name])+1));
        if(song==".")
             return;
        if (strlen(song))
            records[record_name]+=({song});
    }
}

2.1.2 main()

int main(int argc, array(string) argv)
{
    string cmd;
    while(cmd=readline("Command: "))
    {
        string args;
        sscanf(cmd,"%s %s",cmd,args);

        switch(cmd)
        {
        case "list":
            if((int)args)
            {
                show_record((int)args);
            } else {
                list_records();
            }
            break;

        case "quit":
            exit(0);

        case "add":
            add_record();
            break;
        }
    }
}

2.2 Communicating with files

void save(string file_name)
{
    string name, song;
    object o;
    o=Stdio.File();

    if(!o->open(file_name,"wct"))
    {
        write("Failed to open file.\n");
        return;
    }

    foreach(indices(records),name)
    {
         o->write("Record: "+name+"\n");
         foreach(records[name],song)
             o->write("Song: "+song+"\n");
    }

    o->close();
}

2.2.2 load()

void load(string file_name)
{
    object o;
    string name="ERROR";
    string file_contents,line;

    o=Stdio.File();
    if(!o->open(file_name,"r"))
    {
        write("Failed to open file.\n");
        return;
    }

    file_contents=o->read();
    o->close();

    records=([]);

    foreach(file_contents/"\n",line)
    {
        string cmd, arg;
        if(sscanf(line,"%s: %s",cmd,arg))
        {
            switch(lower_case(cmd))
            {
            case "record":
                name=arg;
                records[name]=({});
                break;

             case "song":
                 records[name]+=({arg});
                 break;
            }
        }
    }
}

2.2.3 main() revisited

case "save":
    save(args);
    break;

case "load":
    load(args);
    break;

void delete_record(int num)
{
    array(string) record_names=sort(indices(records));
    string name=record_names[num-1];

    m_delete(records,name);
}

2.3.2 search()

void find_song(string title)
{
    string name, song;
    int hits;

    title=lower_case(title);

    foreach(indices(records),name)
    {
        foreach(records[name],song)
        {
            if(search(lower_case(song), title) != -1)
            {
                write(name+"; "+song+"\n");
                hits++;
            }
        }
    }

    if(!hits) write("Not found.\n");
}

2.3.3 main() again

case "delete":
    delete_record((int)args);
    break;

case "search":
    find_song(args);
    break;

2.4 Then what?

Chapter 3, Control Structures

3.1 Conditions

if( expression ) statement1; else statement2;

1. First it evaluates expression.
   
2. If the result was false go to point 5.
3. Execute statement1.
4. Jump to point 6.
5. Execute statement2.
6. Done.

if( expression )
    statement1;

if( ! expression )
    statement2 ;

if ( ! expression )
{
    statement;
    statement;
    statement;
}

3.1.2 Switch

switch ( expression )
{
    case constant1:
        expressions1;
        break;

    case constant2:
        expressions2;
        break;

    case constant3 .. constant4:
        expressions3;
        break;

    default:
        expressions5;
}

3.2.1 while

while ( expression )
    statement;

int e=1;
while(e<5)
{
    show_record(e);
    e=e+1;
}

3.2.2 for

for ( initializer_statement ; expression ; incrementor_expression )
    statement ;

1. Executes the the initializer_statement. The initializer statement is executed only once and is most commonly used to initialize the loop variable.
2. Evaluates expression
3. If the result was false it exits the loop and continues with the program after the loop.
4. Executes statement.
5. Executes the increment_expression.
6. Starts over from 2.

for(int e=1; e<5; e=e+1)
    show_record(e);

3.2.3 do-while

do
    statement;
while ( expression );

do {
    modem->write("ATDT441-9109\n"); // Dial 441-9109
                } while(modem->gets()[..6]] != "CONNECT");

3.2.4 foreach

foreach ( array_expression, variable )
    statement ;

1. It evaluates the array_expression which must return an array.
2. If the array is empty, exit the loop.
3. It then assigns the first element from the array to the variable.
4. Then it executes the statement.
5. If there are more elements in the array, the next one is assigned to the variable, otherwise exit the loop.
6. Go to point 4.

array tmp1= array_expression;
for ( tmp2 = 0; tmp2 < sizeof(tmp1); tmp2++ )
{
    variable = tmp1 [ tmp2 ];
    statement;
}

3.3.1 break

while(1)
{
    string command=readline("> ");
    if(command=="quit") break;
    do_command(command);
}

3.3.2 continue

while(1)
{
    string command=readline("> ");
    if(strlen(command) == 0) continue;
    if(command=="quit") break;
    do_command(command);
}

3.3.3 return

#!/usr/local/bin/pike

int main()
{
    return 1;
}

3.4 Exercises

Chapter 4, Data types

4.1.1 int

	78	// decimal number
	0116	// octal number
	0x4e	// hexadecimal number
	'N'	// Ascii character

Integers are coded in 2-complement and overflows are silently ignored by Pike. This means that if your integers are 32-bit and you add 1 to the number 2147483647 you get the number -2147483648. This works exactly as in C or C++.

All the arithmetic, bitwise and comparison operators can be used on integers. Also note these functions:

int intp(mixed x)

This function returns 1 if x is an int, 0 otherwise.

int random(int x)

This function returns a random number greater or equal to zero and smaller than x.

int reverse(int x)

This function reverses the order of the bits in x and returns the new number. It is not very useful.

int sqrt(int x)

This computes the square root of x. The value is always rounded down.

4.1.2 float

3.14159265358979323846264338327950288419716939937510 // Pi
1.0e9 // A billion
1.0e-9 // A billionth

All the arithmetic and comparison operators can be used on floats. Also, these functions operates on floats:

trigonometric functions

The trigonometric functions are: sin, asin, cos, acos, tan and atan. If you do not know what these functions do you probably don't need them. Asin, acos and atan are of course short for arc sine, arc cosine and arc tangent. On a calculator they are often known as inverse sine, inverse cosine and inverse tangent.

float log(float x)

This function computes the natural logarithm of x,

float exp(float x)

This function computes e raised to the power of x.

float pow(float x, float y)

This function computes x raised to the power of y.

float sqrt(float x)

This computes the square root of x.

float floor(float x)

This function computes the highest integer value lower or equal to x. Note that the value is returned as a float, not an int.

float ceil(float x),

This function computes the lowest integer value higher or equal to x and returns it as a float.

4.1.3 string

	"hello world" // hello world
	"he" "llo"    // hello
	"\116"        // N (116 is the octal ASCII value for N)
	"\t"          // A tab character
	"\n"          // A newline character
	"\r"          // A carriage return character
	"\b"          // A backspace character
	"\0"          // A null character
	"\""          // A double quote character
	"\\"          // A singe backslash
	"hello world\116\t\n\r\b\0\"\\" // All of the above

Although a string is an array, you can not change the individual characters in the string. Instead you have to construct a new string, here is an example of how:

string s = "hello torld";
s=s[..5]+"w"+s[7..];

All the comparison operators plus the operators listed here can be used on strings:

Summation

Adding strings together will simply concatenate them. "foo"+"bar" becomes "foobar".

Subtraction

Subtracting one string from another will remove all occurrences of the second string from the first one. So "foobarfoogazonk" - "foo" results in "bargazonk".

Indexing

Indexing will let you get the ascii value of any character in a string. The first character is index zero.

Range

The range operator will let you copy any part of the string into a new string. Example: "foobar"[2..4] will return "oba".

Division

Division will let you divide a string at every occurrence of a word or character. For instance if you do "foobargazonk" / "o" the result would be ({"f","","bargaz","nk"}).

Multiplication

The reverse of the division operator can be accomplished by multiplying an array with a string. So if you evaluate ({"f","","bargaz","nk"}) * "o" the result would be "foobargazonk".

Also, these functions operates on strings:

string String.capitalize(string s)

Returns s with the first character converted to upper case.

string lower_case(string s)

Returns s with all the upper case characters converted to lower case.

string replace(string s, string from, string to)

This function replaces all occurrences of the string from in s with to and returns the new string.

string reverse(string s)

This function returns a copy of s with the last byte from s first, the second last in second place and so on.

string search(string haystack, string needle)

This function finds the first occurrence of needle in haystack.

string sizeof(string s)

Same as strlen(s), returns the length of the string.

int stringp(mixed s)

This function returns 1 if s is a string, 0 otherwise.

string strlen(string s)

Returns the length of the string s.

string upper_case(string s)

This function returns s with all lower case characters converted to upper case.

4.2 Pointer types

4.2.1 array

	({ })      // Empty array
	({ 1 })    // Array containing one element of type int
	({ "" })   // Array containing a string
	({ "", 1, 3.0 }) // Array of three elements, each of different type

fig 4.1

Operators and functions usable with arrays:

4.2.2 mapping

fig 4.2

Each index-value pair is floating around freely inside the mapping. There is exactly one value for each index. We also have a (magical) lookup function. This lookup function can find any index in the mapping very quickly. Now, if the mapping is called m and we index it like this: m [ i ] the lookup function will quickly find the index i in the mapping and return the corresponding value. If the index is not found, zero is returned instead. If we on the other hand assign an index in the mapping the value will instead be overwritten with the new value. If the index is not found when assigning, a new index-value pair will be added to the mapping. Writing a constant mapping is easy:

	([ ])       // Empty mapping
	([ 1:2 ])   // Mapping with one index-value pair, the 1 is the index
	([ "one":1, "two":2 ]) // Mapping which maps words to numbers
	([ 1:({2.0}), "":([]), ]) // Mapping with lots of different types

As with arrays, mappings can contain any type. The main difference is that the index can be any type too. Also note that the index-value pairs in a mapping are not stored in a specific order. You can not refer to the fourteenth key-index pair, since there is no way of telling which one is the fourteenth. Because of this, you cannot use the range operator on mappings.

The following operators and functions are important to use mappings:

indexing ( m [ ind ] )

As discussed above, indexing is used to retrieve, store and add values to the mapping.

addition, subtraction, union, intersection and xor

All these operators works exactly as on arrays, with the difference that they operate on the indexes. In those cases when the value can come from either mapping, it will be taken from the right side of the operator. This is to make it easier to add new values to a mapping with +=. Some examples:
([1:3, 3:1]) + ([2:5, 3:7]) returns ([1:3, 2:5, 3:7 ])
([1:3, 3:1]) - ([2:5, 3:7]) returns ([1:3])
([1:3, 3:1]) | ([2:5, 3:7]) returns ([1:3, 2:5, 3:7 ])
([1:3, 3:1]) & ([2:5, 3:7]) returns ([3:7])
([1:3, 3:1]) ^ ([2:5, 3:7]) returns ([1:3, 2:5])

same ( a == b )

Returns 1 if a is the same mapping as b, 0 otherwise.

not same a != b )

Returns 0 if a is the same mapping as b, 1 otherwise.

array indices(mapping m)

Indices returns an array containing all the indexes in the mapping m.

void m_delete(mapping m, mixed ind)

This function removes the index-value pair with the index ind from the mapping m.

int mappingp(mixed m)

This function returns 1 if m is a mapping, 0 otherwise.

mapping mkmapping(array ind, array val)

This function constructs a mapping from the two arrays ind and val. Element 0 in ind and element 0 in val becomes one index-value pair. Element 1 in ind and element 1 in val becomes another index-value pair, and so on..

mapping replace(mapping m, mixed from, mixed to)

This function creates a copy of the mapping m with all values equal to from replaced by to.

mixed search(mapping m, mixed val)

This function returns the index of the 'first' index-value pair which has the value val.

int sizeof(mapping m)

Sizeof returns how many index-value pairs there are in the mapping.

array values(mapping m)

This function does the same as indices, but returns an array with all the values instead. If indices and values are called on the same mapping after each other, without any other mapping operations in between, the returned arrays will be in the same order. They can in turn be used as arguments to mkmapping to rebuild the mapping m again.

int zero_type(mixed t)

When indexing a mapping and the index is not found, zero is returned. However, problems can arise if you have also stored zeroes in the mapping. This function allows you to see the difference between the two cases. If zero_type(m [ ind ]) returns 1, it means that the value was not present in the mapping. If the value was present in the mapping, zero_type will return something else than 1.

4.2.3 multiset

fig 4.3

Instead, the index operator will return 1 if the value was found in the multiset and 0 if it was not. When assigning an index to a multiset like this: mset[ ind ] = val the index ind will be added to the multiset mset if val is true. Otherwise ind will be removed from the multiset instead.

Writing a constant multiset is similar to writing an array:

	(< >)      // Empty multiset
	(< 17 >)  // Multiset with one index: 17
	(< "", 1, 3.0, 1 >) // Multiset with 3 indexes

4.2.4 program

fig 4.4

program p = compile_file("hello_world.pike");

program p = (program) "hello_world";

There is also a way to write programs inside programs with the help of the class keyword:

	class class_name {
	  inherits, variables and functions 
	}

class record {
    string title;
    string artist;
    array(string) songs;
}

array(object(record)) records = ({});

void add_empty_record()
{
    records+=({ record() });
}

void show_record(object(record) rec)
{
    write("Record name: "+rec->title+"\n");
    write("Artist: "+rec->artist+"\n");
    write("Songs:\n");
    foreach(rec->songs, string song)
        write(" "+song+"\n");
}

cloning

To create a data area for a program you need to instantiate or clone the program. This is accomplished by using a pointer to the program as if it was a function and call it. That creates a new object and calls the function create in the new object with the arguments. It is also possible to use the functions new() and clone() which do exactly the same thing except you can use a string to specify what program you want to clone.

compiling

All programs are generated by compiling a file or a string. For this purpose there are two functions:

program compile_file(string filename);
program compile_string(string p, string filename);

Compile_file simply reads the file given as argument, compiles it and returns the resulting program. Compile_string instead compiles whatever is in the string p. The second argument, filename, is only used in debug printouts when an error occurs in the newly made program.

casting

Another way of compiling files to program is to use the cast operator. Casting a string to the type program calls a function in the master object which will compile the program in question for you. The master also keeps the program in a cache, so if you later need the same program again it will not be re-compiled.

int programp(mixed p)

This function returns 1 if p is a program, 0 otherwise.

comparisons

As with all data types == and != can be used to see if two programs are the same or not.

4.2.5 object

fig 4.5

class record {
    string title;
    string artist;
    array(string) songs;

    void show()
    {
        write("Record name: "+title+"\n");
        write("Artist: "+artist+"\n");
                        write("Songs:\n");
                        foreach(songs, string song)
            write(" "+song+"\n");
    }
}

array(object(record)) records = ({});

void add_empty_record()
{
    records+=({ record() });
}

void show_record(object rec)
{
    rec->show();
}

Functions and operators relevant to objects:

indexing

Objects can be indexed on strings to access identifiers. If the identifier is a variable, the value can also be set using indexing. If the identifier is a function, a pointer to that function will be returned. If the identifier is a constant, the value of that constant will be returned. Note that the -> operator is actually the same as indexing. This means that o->foo is the same as o["foo"]

cloning

As discussed in the section about programs, cloning a program can be done in two different ways:

1. Use a pointer to the program as a function and call it.
2. Use the functions new or clone. (They are the same function.)

Whenever you clone an object, all the global variables will be initialized. After that the function create will be called with any arguments you call the program with.

void destruct(object o)

This function invalidates all references to the object o and frees all variables in that object. This function is also called when o runs out of references. If there is a function named destroy in the object, it will be called before the actual destruction of the object.

array(string) indices(object o)

This function returns a list of all identifiers in the object o.

program object_program(object o)

This function returns the program from which o was cloned.

int objectp(mixed o)

This function returns 1 if o is an object, 0 otherwise. Note that if o has been destructed, this function will return 0.

object this_object()

This function returns the object in which the interpreter is currently executing.

array values(object o)

This function returns the same as rows(o,indices(o)). That means it returns all the values of the identifiers in the object o.

comparing

As with all data types == and != can be used to check if two objects are the same or not.

4.2.6 function

fig 4.6

int foo() { return 1; }
function bar() { return foo; }
int gazonk() { return foo(); }
int teleledningsanka() { return bar()(); }

For convenience, there is also a simple way to write a function inside another function. To do this you use the lambda keyword. The syntax is the same as for a normal function, except you write lambda instead of the function name:

lambda ( types ) { statements }

function bar() { return lambda() { return 1; }; )

Note that unlike C++ and Java you can not use function overloading in Pike. This means that you cannot have one function called 'foo' which takes an integer argument and another function 'foo' which takes a float argument.

This is what you can do with a function pointer.

calling ( f ( mixed ... args ) )

As mentioned earlier, all function pointers can be called. In this example the function f is called with the arguments args.

string function_name(function f)

This function returns the name of the function f is pointing at.

object function_object(function f)

This function returns the object the function f is located in.

int functionp(mixed f)

This function returns 1 if f is a function, 0 otherwise. If f is located in a destructed object, 0 is returned.

function this_function()

This function returns a pointer to the function it is called from. This is normally only used with lambda functions because they do not have a name.

4.3 Sharing data

int main(int argc, array(string) argv)
{
    array(string) tmp;
    tmp=argv;
    argv[0]="Hello world.\n";
    write(tmp[0]);
}

Sometimes you want to create a copy of a mapping, array or object. To do so you simply call copy_value with whatever you want to copy as argument. Copy_value is recursive, which means that if you have an array containing arrays, copies will be made of all those arrays.

	int x; // x is an integer
	int|string x; // x is a string or an integer
	array(string) x; // x is an array of strings
	array x; // x is an array of mixed
	mixed x; // x can be any type
	string *x; // x is an array of strings

	 // x is a mapping mapping from int to string
	mapping(string:int) x;

	// x is a clone of Stdio.File
	object(Stdio.File) x;

	// x is a function that takes two integer
	// arguments and returns a string
	function(int,int:string) x;

	// x is a function taking any amount of
	// integer arguments and returns nothing.
	function(int...:void) x;

	// x is ... complicated
	mapping(string:function(string|int...:mapping(string:string*))) x;

mixed

This means that the variable can contain any type, or the function return any value

array( type )

This means an array of type.

type *

This also means an array of type.

mapping( key type : value type )

This is a mapping where the keys are of type key type and the values of value type.

multiset ( type )

This means a multiset containing values of type type.

object ( program )

This means an object cloned from the specified program. The program can be a class, a constant, or a string. If the program is a string it will be casted to a program first. See the documentation for inherit for more information about this casting.

function( argument types : return type )

This is a function taking the specified arguments and returning return type. The argument types is a comma separated list of types that specify the arguments. The argument list can also end with ... to signify that there can be any amount of the last type.

type1 | type2

This means either type1 or type2

void

Void can only be used in certain places, if used as return type for a function it means that the function does not return a value. If used in the argument list for a function it means that that argument can be omitted. Example: function(int|void:void) this means a function that may or may not take an integer argument and does not return a value.

Chapter 5, Operators

5.1 Arithmetic operators

The third column, "Identifier" is the name of the function that actually evaluates the operation. For instance, a + b can also be written as `+(a, b). I will show you how useful this can be at the end of this chapter.

When applied to integers or floats these operators do exactly what they are supposed to do. The only operator in the list not known from basic math is the modulo operator. The modulo operator returns the rest of an integer division. It is the same as calculating a - floor(a / b) * b. floor rounds the value down to closest lower integer value. Note that the call to floor isn't needed when operating on integers, since dividing two integers will return the result as an integer and it is always rounded down. For instance, 8 / 3 would return 2.

If all arguments to the operator are integers, the result will also be an integer. If one is a float and the other is an integer, the result will be a float. If both arguments are float, the result will of course be a float.

However, there are more types in Pike than integers and floats. Here is the complete list of combinations of types you can use with these operators:

5.2 Comparison operators

5.4 Bitwise/set operators

5.6 The assignment operators

variable = expression;

variable1 = variable2 = 1; // Assign 1 to both variables
variable1 =(variable2 = 1); // Same as above

// Write the value of the expression, if any
if(variable = expression)
    write(variable);

object clone(mixed p, mixed ... args) { ( (program)p )(@args); }

On the subject of function calls, the splice operator should also be mentioned. The splice operator is an at sign in front of an expression. The expression should always be an array. The splice operator sends each of the elements in the array as a separate argument to the function call. The splice operator can only be used in an argument list for a function call.

Then there are the increment and decrement operators. The increment and decrement operators are somewhat limited: they can only be used on integers. They provide a short and fast way to add or subtract one to an integer. If the operator is written before the variable (++a) the returned value will be what the variable is after the operator has added/subtracted one to it. If the operator is after the variable (a++) it will instead return the value of the variable before it was incremented/decremented.

Casting is used to convert one type to another, not all casts are possible. Here is a list of all casts that actually _do_ anything:

You can also use the cast operator to tell the compiler things. If a is a variable of type mixed containing an int, then the expression (int)a can be used instead of a and that will tell the compiler that the type of that expression is int.

Last, and in some respect least, is the comma operator. It doesn't do much. In fact, it simply evaluates the two arguments and then returns the right hand one. This operator is mostly useful to produce smaller code, or to make defines that can be used in expressions.

Examples:

5.9 Operator functions

map(arr, `-)

This will return an array with each element negated.

map(text/"\n",`/," ")

This will divide a text into lines, each line will then be mapped through `/ and divided into an array of words.

`+(0, @arr)

This will add all the integers in the array arr together.

int abs(int a) { return ( a>0 ? `+ : `-)(a); }

This is a rather absurd but working function which will return the absolute value of a.

Chapter 6, Object orientation

6.1 Terminology

a class

a class

a clone

an instance of a class

to clone

to create an instance

an object

an instance of a class

a program

a class

6.2 The approach

In my experience, the advantages of object oriented programming are:

Modular programming made easy

Using The approach makes it easy to divide a project into smaller pieces, these pieces are usually easier to write than the whole.

Local data scope

This is a very nifty with object oriented programs. If your program uses several files, windows, stacks, TCP connections or whatever, you simply write a program that handles one such file, window, stack or TCP connection. If correctly written, you can then just create many clones of that program.

Using the same interface to different objects

I can write a function that takes a stream as an argument and writes data to this stream. Later I might wish to write this data to a window instead. I can then create an object that has the same methods as a stream (specifically the write method) and send that to the function that outputs the data.

6.4 Pike and Object Orientation

	program scriptclass=compile_file(argv[0]); // Load script
	object script=scriptclass();               // clone script
	int ret=script->main(sizeof(argv), argv);  // call main()

If you don't want to put each program in a separate file, you can use the class keyword to write all your classes in one file. We have already seen an example how this in chapter 4, but let's go over it in more detail. The syntax looks like this:

class class_name {
    class_definition
}

constant x = 17;
class foobar {
     int test() { return x; }
};

class foo {};
constant foo = class {};

class foo
{
    int test() { return 17; }
};

class bar
{
    program test2() { return foo; }
};

6.5 Inherit

inherit "hello_world";
int main(int argc, array(string) argv)
{
    write("Hello world version 1.0\n");
    return ::main(argc,argv);
}

A string

This will have the same effect as casting the string to a program and then doing inherit on this program.

A constant containing a program.

Any constant from this program, module or inherited program that contains a program can be inherited.

A class name

A class defined with the class keyword is in fact added as a constant, so the same rule as above applies.

Let's look at an example. We'll split up an earlier example into three parts and let each inherit the previous part. It would look something like this:

6.6 Multiple inherit

inherit Stdio.File; // This inherit is named File
inherit Stdio.FILE; // This inherit is named FILE
inherit "hello_word"; // This inherit is named hello_world
inherit Stdio.File : test1; // This inherit is named test1
inherit "hello_world" : test2; // This inherit is named test2

void test()
{
    File::read(); // Read data from the first inherit
    FILE::read(); // Read data from the second inherit
    hello_world::main(0,({})); // Call main in third inherit
    test1::read(); // Read data from fourth inherit
    test2::main(0,({})); // Call main in fourth inherit
    ::read(); // Read data from all inherits
}

If you leave the inherit name blank and just call ::read Pike will call all inherited read() functions. If there is more than one inherited read function the results will be returned in an array.

Let's look at another example:

#!/usr/local/bin/pike

inherit Stdio.File : input;
inherit Stdio.File : output;

int main(int argc, array(string) argv)
{
    output::create("stdout");
    for(int e=1;e<sizeof(argv);e++)
    {
        input::open(argv[e],"r");
                        while(output::write(input::read(4096)) == 4096);
    }
}

6.7 Pike Inherit compared to other languages

6.8 Modifiers

static

Static hides this identifier from the index and arrow operators, which makes it impossible for other objects to call this function unless a function pointer to it is returned from inside this program.

nomask

This prevents other objects from re-defining this identifier in programs that inherit this program.

private

This prevents inheriting programs from accessing this identifier. Note that inheriting program can still re-define the identifier. Also note that private does not imply static.

public

This is the opposite of private. This is the default for all identifiers. public can be used to override the effects of a private inherit.

protected

Reserved for future use.

6.9 Operator Overloading

6.10 Simple exercises

Chapter 7, Miscellaneous functions

7.1 sscanf

int sscanf(string str, string fmt, lvalue ...)

Whenever a percent is found in the format string, a match is according to the following table:

%d	reads an integer
%o	reads an octal integer
%x	reads a hexadecimal integer
%D	reads an integer that is either octal (leading zero), hexadecimal (leading 0x) or decimal.
%f	reads a float
%c	matches one char and returns it as an integer
%2c	matches two chars and returns them as an integer (short)
%s	reads a string. If followed by %d, %s will read any non-numerical characters. If followed by a %[], %s will read any characters not present in the set. If followed by normal text, %s will match all characters up to but not including the first occurrence of that text.
%5s	gives a string of 5 characters (5 can be any number)
%[set]	matches a string containing a given set of characters (those given inside the brackets). %[^set] means any character except those inside brackets. Example: %[0-9H] means any number or 'H'.

If a * is put between the percent and the operator, the operator will only match its argument, not assign any variables.

Sscanf does not use backtracking. Sscanf simply looks at the format string up to the next % and tries to match that with the string. It then proceeds to look at the next part. If a part does not match, sscanf immediately returns how many % were matched. If this happens, the lvalues for % that were not matched will not be changed.

Let's look at a couple of examples:

// a will be assigned "oo" and 1 will be returned
sscanf("foo","f%s",a);

// a will be 4711 and b will be "bar", 2 will be returned
sscanf("4711bar","%d%s",a,b);

// a will become "test"
sscanf(" \t test","%*[ \t]%s",a)

// Remove "the " from the beginning of a string
// If 'str' does not begin with "the " it will not be changed
sscanf(str,"the %s",str);

catch { statements }

({
     "error description",
     backtrace()
})

7.3 gauge

gauge { statements }

7.4 typeof

typeof( exit(1) )

Chapter 8, Modules

here is a list of the basic Pike modules:

Stdio

This module contains file I/O routines.

Array

This function contains functions that operate on arrays.

Gdbm *

This module contains support for Gdbm databases.

Getopt

Routines to parse command line options

Gmp *

Support for large numbers.

Gz *

Deflate packing algorithms.

Image

Image manipulation routines.

LR

LALR(1) parser generator.

Msql *

Sql database support for the mini-SQL database server.

MIME

Support for coding and decoding MIME.

Mysql *

Sql database support for the mySQL database server.

Process

Functions to start and control other processes.

Regexp

Regexp matching routines.

Simulate

Routines to emulate old Pike routines.

String

Routines that operate on strings.

Sql *

Generic SQL database support.

System

Support for system specific functions

Thread *

Thread support functions.

Yp *

Network Information System support.

* These modules might not be available depending on how Pike was compiled and whether support for these functions exist on your system.

8.2 Where do modules come from?

When you use Stdio Pike will look for that module:

1. In the same directory as the source.
2. In directories added with add_module_path()
3. In directories specified with -M on the command line.
4. In directories in the environment variable PIKE_MODULE_PATH
5. In the directory with builtin modules, usually /usr/local/lib/pike/modules/

1. If there is a file called Stdio.pmod.pike, Pike will load this Pike program, clone it and use that as a module.
2. If there is a file called Stdio.pmod.so, Pike will load this with load_module(), clone it and use that as a module.
3. If there is a directory called Stdio.pmod, Pike will create a module containing all the modules in that directory as identifiers. If there is a module called module in that directory, all identifiers from that module will overload any modules actually present in the directory.

8.3 The . operator

8.4 How to write a module

constant PI = 3.14159265358979323846264338327950288419716939937510;
float cos2(float f) { return pow(cos(f),2.0); }

int main()
{
    write(sprintf("%f\n",Trig.cos2(Trig.PI));
}

import Trig;

int main()
{
    write(sprintf("%f\n",cos2(PI));
}

8.5 Simple exercises

Chapter 9, File I/O

9.1 Stdio.File

METHOD

Stdio.File->errno - what was last error?

SYNTAX

int errno();

DESCRIPTION

Returns the error code for the last command on this file. Error code is normally cleared when a command is successful.

9.2 Stdio.FILE

METHOD

Stdio.FILE->gets - get one line

SYNTAX

string gets();

DESCRIPTION

This function returns one line from the FILE, it returns zero if no more lines are available.

METHOD

Stdio.FILE->ungets - put a string back in the buffer

SYNTAX

string ungets(string s);

DESCRIPTION

This function puts a string back in the input buffer. The string can then be read with read, gets or getchar.

METHOD

Stdio.FILE->getchar - get one character from the input stream

SYNTAX

int getchar();

DESCRIPTION

This function returns one character from the input stream. Note that the return value is the ascii value of the character, not a string containing one character.

9.3 Standard streams

Example:

int main()
{
    int line;
    while(string s=Stdio.stdin.gets())
        write(sprintf("%5d: %s\n",line++,s));
}

9.4 Other Stdio functions

FUNCTION

Stdio.werror - write to stderr

SYNTAX

void werror(string s);

DESCRIPTION

Writes a message to stderr. Stderr is normally the console, even if the process output has been redirected to a file or pipe.

9.5 Listening to sockets

9.6 A more complex example - a simple WWW server

Usually WWW involves HTML. HTML (Hyper-Text Markup Language) is a way to write documents with embedded pictures and links to other pages. These links are normally displayed underlined and if you click them your WWW- browser will load whatever document that link leads to.

#!/usr/local/bin/pike

/* A very small httpd capable of fetching files only. * Written by Fredrik Hübinette as a demonstration of Pike. */

inherit Stdio.Port;

Next are some constants that will affect how uHTTPD will operate. This uses the preprocessor directive #define. The preprocessor is the first stage in the compiling process and can make textual processing of the code before it is compiled. As an example, after the first define below, all occurrences of 'BLOCK' will be replaced with 16060.

/* Amount of data moved in one operation */
#define BLOCK 16060

/* Where do we have the html files ? */
#define BASE "/usr/local/html/"

/* File to return when we can't find the file requested */
#define NOFILE "/user/local/html/nofile.html"

/* Port to open */
#define PORT 1905

Next we declare a class called output_class. Later we will clone one instance of this class for each incoming HTTP connection.

class output_class
{
    inherit Stdio.File : socket;
    inherit Stdio.File : file;

    int offset=0;

Next we define the function write_callback(). Later the program will go into a 'waiting' state, until something is received to process, or until there is buffer space available to write output to. When that happens a callback will be called to do this. The write_callback() is called when there is buffer space available. In the following lines 'void' means that it does not return a value. Write callback will be used further down as a callback and will be called whenever there is room in the socket output buffer.

    void write_callback()
    {
        int written;
        string data;

        file::seek(offset);

        data=file::read(BLOCK);

        if(strlen(data))
        {

            written=socket::write(data);

            if(written >= 0)
            {
                offset+=written;
                return;
            }

            werror("Error: "+socket::errno()+".\n");
        }

        destruct(this_object());
    }

Next we need a variable to buffer the input received in. We initialize it to an empty string.

    string input="";

    void read_callback(mixed id,string data)
    {
        string cmd;

        input+=data;

        if(sscanf(input,"%s %s%*[\012\015 \t]",cmd,input)>2)
        {

            if(cmd!="GET")
            {
                werror("Only method GET is supported.\n");
                destruct(this_object());
                return;
            }

            sscanf(input,"%*[/]%s",input);

            input=BASE+combine_path("/",input);

            if(!file::open(input,"r"))
            {

                if(!file::open(NOFILE,"r"))
                {

                    werror("Couldn't find default file.\n");
                    destruct(this_object());
                    return;
                }
            }

            socket::set_buffer(65536,"w");

            socket::set_nonblocking(0,write_callback,0);

            write_callback();

        }
    }

This function is called if the connection is closed while we are reading from the socket.

    void selfdestruct() { destruct(this_object()); }

    void create(object f)
    {
        socket::assign(f);

        socket::set_nonblocking(read_callback,0,selfdestruct);

    }

};

Next we define the function called when someone connects.

void accept_callback()
{
    object tmp_output;

    tmp_output=accept();

    if(!tmp_output) return;

    output_class(tmp_output);

    destruct(tmp_output);

}

int main(int argc, array(string) argv)
{
    werror("Starting minimal httpd\n");

    if(!bind(PORT, accept_callback))
    {
        werror("Failed to open socket (already bound?)\n");
        return 17;
    }

    return - 17; /* Keep going */

}

void foo(int x)
{
    for(int e=0;e<5;e++)
    {
        sleep(1);
        write("Hello from thread "+x+".\n");
    }
}

int main()
{
    thread_create(foo, 2);
    thread_create(foo, 3);
    foo(1);
}

Accessing unlocked data

Look at this code:

void mapadd(mapping m, int i, int j)
{
    if(map[i])
         map[i]+=({j});
    else
         map[i]=({j});
}

This is quite harmless as long as it is only used from one thread at a time, but if two threads call it it at the same time, there is a slight chance that both threads will discover that map[i] is zero and both threads will then do map[i]=({j}); and one value of j will be lost. This type of bug can be extremely hard to debug. The above problem can be solved with the help of Mutexes and Condition variables. Mutexes are basically a way to keep other threads out while a task is being performed. Conditions, or condition variables, are used to inform other threads that they don't have to wait any longer. Pike also provides two different kinds of pipelines to send data from one thread to another, which makes it very simple to write threaded programs. Let's look at an example:

#!/usr/local/bin/pike
import Thread; // We need fifos
inherit Fifo; // Fifo used to supply workers
inherit Fifo : ended; // Fifo used to wait for workers

void worker(string lookfor)
{
    while(string file=Fifo::read())
    {
        int linenum=1;
        object o=Stdio.FILE(file,"r");
        while(string line=o->gets())
        {
            if(search(line, lookfor) >=0)
                write(sprintf("%s:%d: %s\n",file, linenum, line));

            linenum++;
        }
    }
    ended::write(0);
}

int main(int argc, array(string) argv)
{
    for(int e=0;e<4;e++) // Start workers
        thread_create(worker,argv[e]);
    for(int e=2;e<argc;e++) // Feed workers
        Fifo::write(argv[1]);
    for(int e=0;e<4;e++) // Tell workers to die
        Fifo::write(0);
    for(int e=0;e<4;e++) // Wait for workers to die
         ended::read();
    exit(0);
}

This is an example of a simple grep-like program. It looks for the string given as first argument to the program in the files given as the rest of the arguments. Don't worry if you do not understand it yet. Read the descriptions of the functions and classes below and come back and read this example again.

Deadlocks

Deadlocks arise when two threads are waiting for each other to do something. This bug can often arise when several threads need access to a number of resources such as files or other I/O devices. What may happen is that one thread has locked device #1 and is trying to lock device #2 while another thread has locked device #2 and is trying to lock device #1. This type of bug is generally easier to find, but may require a lot of work to fix.

10.2 Threads reference section

NAME

Thread.Mutex - mutex locks

DESCRIPTION

Thread.Mutex is a pre-compiled Pike program that implements mutual exclusion locks. Mutex locks are used to prevent multiple threads from simultaneously execute sections of code which access or change shared data. The basic operations for a mutex is locking and unlocking, if a thread attempts to lock an already locked mutex the thread will sleep until the mutex is unlocked.

NOTA BENE

Mutex locks are only available on systems with POSIX or UNIX threads support.

In POSIX threads, mutex locks can only be unlocked by the same thread locked them. In Pike any thread can unlock a locked mutex.

EXAMPLE

This simple program can be used to exchange data between two programs. It is similar to Thread.Fifo, but can only hold one element of data.

inherit Thread.Mutex : r_mutex;
inherit Thread.Mutex : w_mutex;
object r_lock=r_mutex::lock();
object w_lock;
mixed storage;

void write(mixed data)
{
    w_lock=w_mutex::lock();
    storage=data;
    destruct(r_lock);
}

mixed read()
{
    mixed tmp;
    r_lock=r_mutex::lock();
    tmp=storage;
    storage=0;
    destruct(w_lock);
    return tmp;
}

NAME

Thread.Mutex->lock - lock the mutex

SYNTAX

object lock();

DESCRIPTION

This function attempts to lock the mutex, if the mutex is already locked the current thread will sleep until the lock is unlocked by some other thread. The value returned is the 'key' to the lock. When the key is destructed or has no more references the lock will automatically be unlocked. The key will also be destructed if the lock is destructed.

NAME

Thread.Mutex->trylock - try to lock the mutex

SYNTAX

object trylock();

DESCRIPTION

This function performs the same operation as lock(), but if the mutex is already locked zero will be returned instead of sleeping until the lock is unlocked.

NAME

Thread.Condition->signal - signal a condition variable

SYNTAX

void signal();

DESCRIPTION

Signal wakes up one of the threads currently waiting for the condition.

BUGS

It sometimes wakes up more than one thread.

NAME

Thread.Condition->broadcast - signal all waiting threads

SYNTAX

void broadcast();

DESCRIPTION

This function wakes up all threads currently waiting for this condition.

NAME

Thread.Fifo->create - initialize the fifo

SYNTAX

void create(int size);
or
object(Thread.Fifo) Thread.Fifo();
or
object(Thread.Fifo) Thread.Fifo(int size);

DESCRIPTION

The function create() is called when the fifo is cloned, if the optional size argument is present it sets how many values can be written to the fifo without blocking. The default size is 128.

NAME

Thread.Fifo->write - queue a value

SYNTAX

void write(mixed value);

DESCRIPTION

This function puts a value last in the fifo. If there is no more room in the fifo the current thread will sleep until space is available.

NAME

Thread.Fifo->read - read a value from the fifo

SYNTAX

mixed read();

DESCRIPTION

This function retrieves a value from the fifo. Values will be returned in the order they were written. If there are no values present in the fifo the current thread will sleep until some other thread writes a value to the fifo.

NAME

Thread.Fifo->size - return number of values in fifo

SYNTAX

int size();

DESCRIPTION

This function returns how many values are currently in the fifo.

NAME

Thread.Queue->write - queue a value

SYNTAX

void write(mixed value);

DESCRIPTION

This function puts a value last in the queue. If the queue is too small to hold the value the queue will be expanded to make room for it.

NAME

Thread.Queue->read - read a value from the queue

SYNTAX

mixed read();

DESCRIPTION

This function retrieves a value from the queue. Values will be returned in the order they were written. If there are no values present in the queue the current thread will sleep until some other thread writes a value to the queue.

NAME

Thread.Queue->size - return number of values in queue

SYNTAX

int queue->size();

DESCRIPTION

This function returns how many values are currently in the queue.

10.3 Threads example

11.1 String

NAME

String.implode_nicely - make an English comma separated list

SYNTAX

string implode_nicely(array(string) words, string|void separator)

DESCRIPTION

This function implodes a list of words to a readable string. If the separator is omitted, the default is "and".

EXAMPLES

> implode_nicely(({"green"}));
Result: green
> implode_nicely(({"green","blue"}));
Result: green and blue
> implode_nicely(({"green","blue","white"}));
Result: green, blue and white
> implode_nicely(({"green","blue","white"}),"or");
Result: green, blue or white

SEE ALSO

`*

NAME

String.strmult - multiply strings

SYNTAX

string strmult(string s, int num);

DESCRIPTION

This function multiplies 's' by 'num'. The return value is the same as appending 's' to an empty string 'num' times.

11.2 Array

NAME

Array.uniq - return one of each element

SYNTAX

array uniq(array a);

DESCRIPTION

This function returns an copy of the array a with all duplicate values removed. The order of the values in the result is undefined.

Chapter 12, Image

All images handled by this module are stored as 24-bit RGB images. This means that a 1024 pixel wide and 1024 pixel high image will use 1024*1024*3 bytes = 3 megabytes. It is quite easy to mess up and use up all the memory by giving the wrong argument to one of the scaling functions.

Most functions in this module work by creating a new Image and then returning that instead of changing the Image you are working with. This makes it possible to share the same image between many variables without having to worry that it will be changed by accident. This can reduce the amount of memory used.

Many functions in this module work with the 'current color', this can be thought of as the background color if you wish. To change the current color you use 'setcolor'.

Let's look at an example of how this can be used:

#!/usr/local/bin/pike

int main()
{
    write("Content-type: image/gif\n\n");
    object font=Image.font();
    font->load("testfont");
    object image=font->write(ctime(time));
    write(image->togif());
}

NAME

Image

DESCRIPTION

This module adds image-drawing and -manipulating capabilities to pike.

Image.image	Basic image manipulation
Image.font	Creating images from text
Image.colortable	Color reduction, quantisation and dither
Image.GIF	GIF encoding/decoding capabilities
Image.PNM	PNM (PBM/PGM/PPM) encoding/decoding capabilities

NOTA BENE

Image module documentation is based on these file versions:
     $Id: blit.c,v 1.24 1997/11/24 16:11:55 mirar Exp $
     $Id: blit_layer_include.h,v 1.4 1997/10/27 22:41:17 mirar Exp $
     $Id: colortable.c,v 1.27 1997/11/29 22:47:39 mirar Exp $
     $Id: colortable.h,v 1.10 1997/11/11 22:17:47 mirar Exp $
     $Id: dct.c,v 1.9 1997/10/27 22:41:19 mirar Exp $
     $Id: font.c,v 1.21 1997/11/11 22:17:48 mirar Exp $
     $Id: image.c,v 1.69 1997/11/29 18:59:35 hedda Exp $
     $Id: image.h,v 1.15 1997/11/23 05:28:29 per Exp $
     $Id: matrix.c,v 1.10 1997/10/27 22:41:25 mirar Exp $
     $Id: operator.c,v 1.9 1997/10/27 22:41:26 mirar Exp $
     $Id: pattern.c,v 1.9 1997/11/02 18:49:11 grubba Exp $
     $Id: pnm.c,v 1.8 1997/11/02 03:46:52 mirar Exp $
     $Id: polyfill.c,v 1.15 1997/11/12 03:40:20 mirar Exp $
     $Id: togif.c,v 1.28 1997/11/26 15:41:35 mirar Exp $
     $Id: gif.c,v 1.20 1997/11/29 22:48:50 mirar Exp $
     $Id: gif_lzw.c,v 1.4 1997/11/05 03:42:50 mirar Exp $
     $Id: gif_lzw.h,v 1.4 1997/11/02 03:44:51 mirar Exp $
     $Id: pnm.c,v 1.5 1997/11/29 21:33:36 grubba Exp $
     

12.1 Image.colortable

NAME

Image.colortable->cast

SYNTAX

object cast(string to)

DESCRIPTION

cast the colortable to an array

example: (array)Image.colortable(img)

ARGUMENTS

argument(s)	description
string to	must be "array".

RETURN VALUE

the resulting array