This is libc.info, produced by makeinfo version 4.2 from libc.texinfo. INFO-DIR-SECTION GNU libraries START-INFO-DIR-ENTRY * Libc: (libc). C library. END-INFO-DIR-ENTRY This file documents the GNU C library. This is Edition 0.10, last updated 2001-07-06, of `The GNU C Library Reference Manual', for Version 2.3.x. Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software Needs Free Documentation" and "GNU Lesser General Public License", the Front-Cover texts being (a) (see below), and with the Back-Cover Texts being (b) (see below). A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Front-Cover Text is: A GNU Manual (b) The FSF's Back-Cover Text is: You have freedom to copy and modify this GNU Manual, like GNU software. Copies published by the Free Software Foundation raise funds for GNU development.  File: libc.info, Node: Setting the Locale, Next: Standard Locales, Prev: Locale Categories, Up: Locales How Programs Set the Locale =========================== A C program inherits its locale environment variables when it starts up. This happens automatically. However, these variables do not automatically control the locale used by the library functions, because ISO C says that all programs start by default in the standard `C' locale. To use the locales specified by the environment, you must call `setlocale'. Call it as follows: setlocale (LC_ALL, ""); to select a locale based on the user choice of the appropriate environment variables. You can also use `setlocale' to specify a particular locale, for general use or for a specific category. The symbols in this section are defined in the header file `locale.h'. - Function: char * setlocale (int CATEGORY, const char *LOCALE) The function `setlocale' sets the current locale for category CATEGORY to LOCALE. A list of all the locales the system provides can be created by running locale -a If CATEGORY is `LC_ALL', this specifies the locale for all purposes. The other possible values of CATEGORY specify an single purpose (*note Locale Categories::). You can also use this function to find out the current locale by passing a null pointer as the LOCALE argument. In this case, `setlocale' returns a string that is the name of the locale currently selected for category CATEGORY. The string returned by `setlocale' can be overwritten by subsequent calls, so you should make a copy of the string (*note Copying and Concatenation::) if you want to save it past any further calls to `setlocale'. (The standard library is guaranteed never to call `setlocale' itself.) You should not modify the string returned by `setlocale'. It might be the same string that was passed as an argument in a previous call to `setlocale'. One requirement is that the CATEGORY must be the same in the call the string was returned and the one when the string is passed in as LOCALE parameter. When you read the current locale for category `LC_ALL', the value encodes the entire combination of selected locales for all categories. In this case, the value is not just a single locale name. In fact, we don't make any promises about what it looks like. But if you specify the same "locale name" with `LC_ALL' in a subsequent call to `setlocale', it restores the same combination of locale selections. To be sure you can use the returned string encoding the currently selected locale at a later time, you must make a copy of the string. It is not guaranteed that the returned pointer remains valid over time. When the LOCALE argument is not a null pointer, the string returned by `setlocale' reflects the newly-modified locale. If you specify an empty string for LOCALE, this means to read the appropriate environment variable and use its value to select the locale for CATEGORY. If a nonempty string is given for LOCALE, then the locale of that name is used if possible. If you specify an invalid locale name, `setlocale' returns a null pointer and leaves the current locale unchanged. Here is an example showing how you might use `setlocale' to temporarily switch to a new locale. #include #include #include #include void with_other_locale (char *new_locale, void (*subroutine) (int), int argument) { char *old_locale, *saved_locale; /* Get the name of the current locale. */ old_locale = setlocale (LC_ALL, NULL); /* Copy the name so it won't be clobbered by `setlocale'. */ saved_locale = strdup (old_locale); if (saved_locale == NULL) fatal ("Out of memory"); /* Now change the locale and do some stuff with it. */ setlocale (LC_ALL, new_locale); (*subroutine) (argument); /* Restore the original locale. */ setlocale (LC_ALL, saved_locale); free (saved_locale); } *Portability Note:* Some ISO C systems may define additional locale categories, and future versions of the library will do so. For portability, assume that any symbol beginning with `LC_' might be defined in `locale.h'.  File: libc.info, Node: Standard Locales, Next: Locale Information, Prev: Setting the Locale, Up: Locales Standard Locales ================ The only locale names you can count on finding on all operating systems are these three standard ones: `"C"' This is the standard C locale. The attributes and behavior it provides are specified in the ISO C standard. When your program starts up, it initially uses this locale by default. `"POSIX"' This is the standard POSIX locale. Currently, it is an alias for the standard C locale. `""' The empty name says to select a locale based on environment variables. *Note Locale Categories::. Defining and installing named locales is normally a responsibility of the system administrator at your site (or the person who installed the GNU C library). It is also possible for the user to create private locales. All this will be discussed later when describing the tool to do so. If your program needs to use something other than the `C' locale, it will be more portable if you use whatever locale the user specifies with the environment, rather than trying to specify some non-standard locale explicitly by name. Remember, different machines might have different sets of locales installed.  File: libc.info, Node: Locale Information, Next: Formatting Numbers, Prev: Standard Locales, Up: Locales Accessing Locale Information ============================ There are several ways to access locale information. The simplest way is to let the C library itself do the work. Several of the functions in this library implicitly access the locale data, and use what information is provided by the currently selected locale. This is how the locale model is meant to work normally. As an example take the `strftime' function, which is meant to nicely format date and time information (*note Formatting Calendar Time::). Part of the standard information contained in the `LC_TIME' category is the names of the months. Instead of requiring the programmer to take care of providing the translations the `strftime' function does this all by itself. `%A' in the format string is replaced by the appropriate weekday name of the locale currently selected by `LC_TIME'. This is an easy example, and wherever possible functions do things automatically in this way. But there are quite often situations when there is simply no function to perform the task, or it is simply not possible to do the work automatically. For these cases it is necessary to access the information in the locale directly. To do this the C library provides two functions: `localeconv' and `nl_langinfo'. The former is part of ISO C and therefore portable, but has a brain-damaged interface. The second is part of the Unix interface and is portable in as far as the system follows the Unix standards. * Menu: * The Lame Way to Locale Data:: ISO C's `localeconv'. * The Elegant and Fast Way:: X/Open's `nl_langinfo'.  File: libc.info, Node: The Lame Way to Locale Data, Next: The Elegant and Fast Way, Up: Locale Information `localeconv': It is portable but ... ------------------------------------ Together with the `setlocale' function the ISO C people invented the `localeconv' function. It is a masterpiece of poor design. It is expensive to use, not extendable, and not generally usable as it provides access to only `LC_MONETARY' and `LC_NUMERIC' related information. Nevertheless, if it is applicable to a given situation it should be used since it is very portable. The function `strfmon' formats monetary amounts according to the selected locale using this information. - Function: struct lconv * localeconv (void) The `localeconv' function returns a pointer to a structure whose components contain information about how numeric and monetary values should be formatted in the current locale. You should not modify the structure or its contents. The structure might be overwritten by subsequent calls to `localeconv', or by calls to `setlocale', but no other function in the library overwrites this value. - Data Type: struct lconv `localeconv''s return value is of this data type. Its elements are described in the following subsections. If a member of the structure `struct lconv' has type `char', and the value is `CHAR_MAX', it means that the current locale has no value for that parameter. * Menu: * General Numeric:: Parameters for formatting numbers and currency amounts. * Currency Symbol:: How to print the symbol that identifies an amount of money (e.g. `$'). * Sign of Money Amount:: How to print the (positive or negative) sign for a monetary amount, if one exists.  File: libc.info, Node: General Numeric, Next: Currency Symbol, Up: The Lame Way to Locale Data Generic Numeric Formatting Parameters ..................................... These are the standard members of `struct lconv'; there may be others. `char *decimal_point' `char *mon_decimal_point' These are the decimal-point separators used in formatting non-monetary and monetary quantities, respectively. In the `C' locale, the value of `decimal_point' is `"."', and the value of `mon_decimal_point' is `""'. `char *thousands_sep' `char *mon_thousands_sep' These are the separators used to delimit groups of digits to the left of the decimal point in formatting non-monetary and monetary quantities, respectively. In the `C' locale, both members have a value of `""' (the empty string). `char *grouping' `char *mon_grouping' These are strings that specify how to group the digits to the left of the decimal point. `grouping' applies to non-monetary quantities and `mon_grouping' applies to monetary quantities. Use either `thousands_sep' or `mon_thousands_sep' to separate the digit groups. Each member of these strings is to be interpreted as an integer value of type `char'. Successive numbers (from left to right) give the sizes of successive groups (from right to left, starting at the decimal point.) The last member is either `0', in which case the previous member is used over and over again for all the remaining groups, or `CHAR_MAX', in which case there is no more grouping--or, put another way, any remaining digits form one large group without separators. For example, if `grouping' is `"\04\03\02"', the correct grouping for the number `123456787654321' is `12', `34', `56', `78', `765', `4321'. This uses a group of 4 digits at the end, preceded by a group of 3 digits, preceded by groups of 2 digits (as many as needed). With a separator of `,', the number would be printed as `12,34,56,78,765,4321'. A value of `"\03"' indicates repeated groups of three digits, as normally used in the U.S. In the standard `C' locale, both `grouping' and `mon_grouping' have a value of `""'. This value specifies no grouping at all. `char int_frac_digits' `char frac_digits' These are small integers indicating how many fractional digits (to the right of the decimal point) should be displayed in a monetary value in international and local formats, respectively. (Most often, both members have the same value.) In the standard `C' locale, both of these members have the value `CHAR_MAX', meaning "unspecified". The ISO standard doesn't say what to do when you find this value; we recommend printing no fractional digits. (This locale also specifies the empty string for `mon_decimal_point', so printing any fractional digits would be confusing!)  File: libc.info, Node: Currency Symbol, Next: Sign of Money Amount, Prev: General Numeric, Up: The Lame Way to Locale Data Printing the Currency Symbol ............................ These members of the `struct lconv' structure specify how to print the symbol to identify a monetary value--the international analog of `$' for US dollars. Each country has two standard currency symbols. The "local currency symbol" is used commonly within the country, while the "international currency symbol" is used internationally to refer to that country's currency when it is necessary to indicate the country unambiguously. For example, many countries use the dollar as their monetary unit, and when dealing with international currencies it's important to specify that one is dealing with (say) Canadian dollars instead of U.S. dollars or Australian dollars. But when the context is known to be Canada, there is no need to make this explicit--dollar amounts are implicitly assumed to be in Canadian dollars. `char *currency_symbol' The local currency symbol for the selected locale. In the standard `C' locale, this member has a value of `""' (the empty string), meaning "unspecified". The ISO standard doesn't say what to do when you find this value; we recommend you simply print the empty string as you would print any other string pointed to by this variable. `char *int_curr_symbol' The international currency symbol for the selected locale. The value of `int_curr_symbol' should normally consist of a three-letter abbreviation determined by the international standard `ISO 4217 Codes for the Representation of Currency and Funds', followed by a one-character separator (often a space). In the standard `C' locale, this member has a value of `""' (the empty string), meaning "unspecified". We recommend you simply print the empty string as you would print any other string pointed to by this variable. `char p_cs_precedes' `char n_cs_precedes' `char int_p_cs_precedes' `char int_n_cs_precedes' These members are `1' if the `currency_symbol' or `int_curr_symbol' strings should precede the value of a monetary amount, or `0' if the strings should follow the value. The `p_cs_precedes' and `int_p_cs_precedes' members apply to positive amounts (or zero), and the `n_cs_precedes' and `int_n_cs_precedes' members apply to negative amounts. In the standard `C' locale, all of these members have a value of `CHAR_MAX', meaning "unspecified". The ISO standard doesn't say what to do when you find this value. We recommend printing the currency symbol before the amount, which is right for most countries. In other words, treat all nonzero values alike in these members. The members with the `int_' prefix apply to the `int_curr_symbol' while the other two apply to `currency_symbol'. `char p_sep_by_space' `char n_sep_by_space' `char int_p_sep_by_space' `char int_n_sep_by_space' These members are `1' if a space should appear between the `currency_symbol' or `int_curr_symbol' strings and the amount, or `0' if no space should appear. The `p_sep_by_space' and `int_p_sep_by_space' members apply to positive amounts (or zero), and the `n_sep_by_space' and `int_n_sep_by_space' members apply to negative amounts. In the standard `C' locale, all of these members have a value of `CHAR_MAX', meaning "unspecified". The ISO standard doesn't say what you should do when you find this value; we suggest you treat it as 1 (print a space). In other words, treat all nonzero values alike in these members. The members with the `int_' prefix apply to the `int_curr_symbol' while the other two apply to `currency_symbol'. There is one specialty with the `int_curr_symbol', though. Since all legal values contain a space at the end the string one either printf this space (if the currency symbol must appear in front and must be separated) or one has to avoid printing this character at all (especially when at the end of the string).  File: libc.info, Node: Sign of Money Amount, Prev: Currency Symbol, Up: The Lame Way to Locale Data Printing the Sign of a Monetary Amount ...................................... These members of the `struct lconv' structure specify how to print the sign (if any) of a monetary value. `char *positive_sign' `char *negative_sign' These are strings used to indicate positive (or zero) and negative monetary quantities, respectively. In the standard `C' locale, both of these members have a value of `""' (the empty string), meaning "unspecified". The ISO standard doesn't say what to do when you find this value; we recommend printing `positive_sign' as you find it, even if it is empty. For a negative value, print `negative_sign' as you find it unless both it and `positive_sign' are empty, in which case print `-' instead. (Failing to indicate the sign at all seems rather unreasonable.) `char p_sign_posn' `char n_sign_posn' `char int_p_sign_posn' `char int_n_sign_posn' These members are small integers that indicate how to position the sign for nonnegative and negative monetary quantities, respectively. (The string used by the sign is what was specified with `positive_sign' or `negative_sign'.) The possible values are as follows: `0' The currency symbol and quantity should be surrounded by parentheses. `1' Print the sign string before the quantity and currency symbol. `2' Print the sign string after the quantity and currency symbol. `3' Print the sign string right before the currency symbol. `4' Print the sign string right after the currency symbol. `CHAR_MAX' "Unspecified". Both members have this value in the standard `C' locale. The ISO standard doesn't say what you should do when the value is `CHAR_MAX'. We recommend you print the sign after the currency symbol. The members with the `int_' prefix apply to the `int_curr_symbol' while the other two apply to `currency_symbol'.  File: libc.info, Node: The Elegant and Fast Way, Prev: The Lame Way to Locale Data, Up: Locale Information Pinpoint Access to Locale Data ------------------------------ When writing the X/Open Portability Guide the authors realized that the `localeconv' function is not enough to provide reasonable access to locale information. The information which was meant to be available in the locale (as later specified in the POSIX.1 standard) requires more ways to access it. Therefore the `nl_langinfo' function was introduced. - Function: char * nl_langinfo (nl_item ITEM) The `nl_langinfo' function can be used to access individual elements of the locale categories. Unlike the `localeconv' function, which returns all the information, `nl_langinfo' lets the caller select what information it requires. This is very fast and it is not a problem to call this function multiple times. A second advantage is that in addition to the numeric and monetary formatting information, information from the `LC_TIME' and `LC_MESSAGES' categories is available. The type `nl_type' is defined in `nl_types.h'. The argument ITEM is a numeric value defined in the header `langinfo.h'. The X/Open standard defines the following values: `CODESET' `nl_langinfo' returns a string with the name of the coded character set used in the selected locale. `ABDAY_1' `ABDAY_2' `ABDAY_3' `ABDAY_4' `ABDAY_5' `ABDAY_6' `ABDAY_7' `nl_langinfo' returns the abbreviated weekday name. `ABDAY_1' corresponds to Sunday. `DAY_1' `DAY_2' `DAY_3' `DAY_4' `DAY_5' `DAY_6' `DAY_7' Similar to `ABDAY_1' etc., but here the return value is the unabbreviated weekday name. `ABMON_1' `ABMON_2' `ABMON_3' `ABMON_4' `ABMON_5' `ABMON_6' `ABMON_7' `ABMON_8' `ABMON_9' `ABMON_10' `ABMON_11' `ABMON_12' The return value is abbreviated name of the month. `ABMON_1' corresponds to January. `MON_1' `MON_2' `MON_3' `MON_4' `MON_5' `MON_6' `MON_7' `MON_8' `MON_9' `MON_10' `MON_11' `MON_12' Similar to `ABMON_1' etc., but here the month names are not abbreviated. Here the first value `MON_1' also corresponds to January. `AM_STR' `PM_STR' The return values are strings which can be used in the representation of time as an hour from 1 to 12 plus an am/pm specifier. Note that in locales which do not use this time representation these strings might be empty, in which case the am/pm format cannot be used at all. `D_T_FMT' The return value can be used as a format string for `strftime' to represent time and date in a locale-specific way. `D_FMT' The return value can be used as a format string for `strftime' to represent a date in a locale-specific way. `T_FMT' The return value can be used as a format string for `strftime' to represent time in a locale-specific way. `T_FMT_AMPM' The return value can be used as a format string for `strftime' to represent time in the am/pm format. Note that if the am/pm format does not make any sense for the selected locale, the return value might be the same as the one for `T_FMT'. `ERA' The return value represents the era used in the current locale. Most locales do not define this value. An example of a locale which does define this value is the Japanese one. In Japan, the traditional representation of dates includes the name of the era corresponding to the then-emperor's reign. Normally it should not be necessary to use this value directly. Specifying the `E' modifier in their format strings causes the `strftime' functions to use this information. The format of the returned string is not specified, and therefore you should not assume knowledge of it on different systems. `ERA_YEAR' The return value gives the year in the relevant era of the locale. As for `ERA' it should not be necessary to use this value directly. `ERA_D_T_FMT' This return value can be used as a format string for `strftime' to represent dates and times in a locale-specific era-based way. `ERA_D_FMT' This return value can be used as a format string for `strftime' to represent a date in a locale-specific era-based way. `ERA_T_FMT' This return value can be used as a format string for `strftime' to represent time in a locale-specific era-based way. `ALT_DIGITS' The return value is a representation of up to 100 values used to represent the values 0 to 99. As for `ERA' this value is not intended to be used directly, but instead indirectly through the `strftime' function. When the modifier `O' is used in a format which would otherwise use numerals to represent hours, minutes, seconds, weekdays, months, or weeks, the appropriate value for the locale is used instead. `INT_CURR_SYMBOL' The same as the value returned by `localeconv' in the `int_curr_symbol' element of the `struct lconv'. `CURRENCY_SYMBOL' `CRNCYSTR' The same as the value returned by `localeconv' in the `currency_symbol' element of the `struct lconv'. `CRNCYSTR' is a deprecated alias still required by Unix98. `MON_DECIMAL_POINT' The same as the value returned by `localeconv' in the `mon_decimal_point' element of the `struct lconv'. `MON_THOUSANDS_SEP' The same as the value returned by `localeconv' in the `mon_thousands_sep' element of the `struct lconv'. `MON_GROUPING' The same as the value returned by `localeconv' in the `mon_grouping' element of the `struct lconv'. `POSITIVE_SIGN' The same as the value returned by `localeconv' in the `positive_sign' element of the `struct lconv'. `NEGATIVE_SIGN' The same as the value returned by `localeconv' in the `negative_sign' element of the `struct lconv'. `INT_FRAC_DIGITS' The same as the value returned by `localeconv' in the `int_frac_digits' element of the `struct lconv'. `FRAC_DIGITS' The same as the value returned by `localeconv' in the `frac_digits' element of the `struct lconv'. `P_CS_PRECEDES' The same as the value returned by `localeconv' in the `p_cs_precedes' element of the `struct lconv'. `P_SEP_BY_SPACE' The same as the value returned by `localeconv' in the `p_sep_by_space' element of the `struct lconv'. `N_CS_PRECEDES' The same as the value returned by `localeconv' in the `n_cs_precedes' element of the `struct lconv'. `N_SEP_BY_SPACE' The same as the value returned by `localeconv' in the `n_sep_by_space' element of the `struct lconv'. `P_SIGN_POSN' The same as the value returned by `localeconv' in the `p_sign_posn' element of the `struct lconv'. `N_SIGN_POSN' The same as the value returned by `localeconv' in the `n_sign_posn' element of the `struct lconv'. `INT_P_CS_PRECEDES' The same as the value returned by `localeconv' in the `int_p_cs_precedes' element of the `struct lconv'. `INT_P_SEP_BY_SPACE' The same as the value returned by `localeconv' in the `int_p_sep_by_space' element of the `struct lconv'. `INT_N_CS_PRECEDES' The same as the value returned by `localeconv' in the `int_n_cs_precedes' element of the `struct lconv'. `INT_N_SEP_BY_SPACE' The same as the value returned by `localeconv' in the `int_n_sep_by_space' element of the `struct lconv'. `INT_P_SIGN_POSN' The same as the value returned by `localeconv' in the `int_p_sign_posn' element of the `struct lconv'. `INT_N_SIGN_POSN' The same as the value returned by `localeconv' in the `int_n_sign_posn' element of the `struct lconv'. `DECIMAL_POINT' `RADIXCHAR' The same as the value returned by `localeconv' in the `decimal_point' element of the `struct lconv'. The name `RADIXCHAR' is a deprecated alias still used in Unix98. `THOUSANDS_SEP' `THOUSEP' The same as the value returned by `localeconv' in the `thousands_sep' element of the `struct lconv'. The name `THOUSEP' is a deprecated alias still used in Unix98. `GROUPING' The same as the value returned by `localeconv' in the `grouping' element of the `struct lconv'. `YESEXPR' The return value is a regular expression which can be used with the `regex' function to recognize a positive response to a yes/no question. The GNU C library provides the `rpmatch' function for easier handling in applications. `NOEXPR' The return value is a regular expression which can be used with the `regex' function to recognize a negative response to a yes/no question. `YESSTR' The return value is a locale-specific translation of the positive response to a yes/no question. Using this value is deprecated since it is a very special case of message translation, and is better handled by the message translation functions (*note Message Translation::). The use of this symbol is deprecated. Instead message translation should be used. `NOSTR' The return value is a locale-specific translation of the negative response to a yes/no question. What is said for `YESSTR' is also true here. The use of this symbol is deprecated. Instead message translation should be used. The file `langinfo.h' defines a lot more symbols but none of them is official. Using them is not portable, and the format of the return values might change. Therefore we recommended you not use them. Note that the return value for any valid argument can be used for in all situations (with the possible exception of the am/pm time formatting codes). If the user has not selected any locale for the appropriate category, `nl_langinfo' returns the information from the `"C"' locale. It is therefore possible to use this function as shown in the example below. If the argument ITEM is not valid, a pointer to an empty string is returned. An example of `nl_langinfo' usage is a function which has to print a given date and time in a locale-specific way. At first one might think that, since `strftime' internally uses the locale information, writing something like the following is enough: size_t i18n_time_n_data (char *s, size_t len, const struct tm *tp) { return strftime (s, len, "%X %D", tp); } The format contains no weekday or month names and therefore is internationally usable. Wrong! The output produced is something like `"hh:mm:ss MM/DD/YY"'. This format is only recognizable in the USA. Other countries use different formats. Therefore the function should be rewritten like this: size_t i18n_time_n_data (char *s, size_t len, const struct tm *tp) { return strftime (s, len, nl_langinfo (D_T_FMT), tp); } Now it uses the date and time format of the locale selected when the program runs. If the user selects the locale correctly there should never be a misunderstanding over the time and date format.  File: libc.info, Node: Formatting Numbers, Next: Yes-or-No Questions, Prev: Locale Information, Up: Locales A dedicated function to format numbers ====================================== We have seen that the structure returned by `localeconv' as well as the values given to `nl_langinfo' allow you to retrieve the various pieces of locale-specific information to format numbers and monetary amounts. We have also seen that the underlying rules are quite complex. Therefore the X/Open standards introduce a function which uses such locale information, making it easier for the user to format numbers according to these rules. - Function: ssize_t strfmon (char *S, size_t MAXSIZE, const char *FORMAT, ...) The `strfmon' function is similar to the `strftime' function in that it takes a buffer, its size, a format string, and values to write into the buffer as text in a form specified by the format string. Like `strftime', the function also returns the number of bytes written into the buffer. There are two differences: `strfmon' can take more than one argument, and, of course, the format specification is different. Like `strftime', the format string consists of normal text, which is output as is, and format specifiers, which are indicated by a `%'. Immediately after the `%', you can optionally specify various flags and formatting information before the main formatting character, in a similar way to `printf': * Immediately following the `%' there can be one or more of the following flags: `=F' The single byte character F is used for this field as the numeric fill character. By default this character is a space character. Filling with this character is only performed if a left precision is specified. It is not just to fill to the given field width. `^' The number is printed without grouping the digits according to the rules of the current locale. By default grouping is enabled. `+', `(' At most one of these flags can be used. They select which format to represent the sign of a currency amount. By default, and if `+' is given, the locale equivalent of +/- is used. If `(' is given, negative amounts are enclosed in parentheses. The exact format is determined by the values of the `LC_MONETARY' category of the locale selected at program runtime. `!' The output will not contain the currency symbol. `-' The output will be formatted left-justified instead of right-justified if it does not fill the entire field width. The next part of a specification is an optional field width. If no width is specified 0 is taken. During output, the function first determines how much space is required. If it requires at least as many characters as given by the field width, it is output using as much space as necessary. Otherwise, it is extended to use the full width by filling with the space character. The presence or absence of the `-' flag determines the side at which such padding occurs. If present, the spaces are added at the right making the output left-justified, and vice versa. So far the format looks familiar, being similar to the `printf' and `strftime' formats. However, the next two optional fields introduce something new. The first one is a `#' character followed by a decimal digit string. The value of the digit string specifies the number of _digit_ positions to the left of the decimal point (or equivalent). This does _not_ include the grouping character when the `^' flag is not given. If the space needed to print the number does not fill the whole width, the field is padded at the left side with the fill character, which can be selected using the `=' flag and by default is a space. For example, if the field width is selected as 6 and the number is 123, the fill character is `*' the result will be `***123'. The second optional field starts with a `.' (period) and consists of another decimal digit string. Its value describes the number of characters printed after the decimal point. The default is selected from the current locale (`frac_digits', `int_frac_digits', see *note General Numeric::). If the exact representation needs more digits than given by the field width, the displayed value is rounded. If the number of fractional digits is selected to be zero, no decimal point is printed. As a GNU extension, the `strfmon' implementation in the GNU libc allows an optional `L' next as a format modifier. If this modifier is given, the argument is expected to be a `long double' instead of a `double' value. Finally, the last component is a format specifier. There are three specifiers defined: `i' Use the locale's rules for formatting an international currency value. `n' Use the locale's rules for formatting a national currency value. `%' Place a `%' in the output. There must be no flag, width specifier or modifier given, only `%%' is allowed. As for `printf', the function reads the format string from left to right and uses the values passed to the function following the format string. The values are expected to be either of type `double' or `long double', depending on the presence of the modifier `L'. The result is stored in the buffer pointed to by S. At most MAXSIZE characters are stored. The return value of the function is the number of characters stored in S, including the terminating `NULL' byte. If the number of characters stored would exceed MAXSIZE, the function returns -1 and the content of the buffer S is unspecified. In this case `errno' is set to `E2BIG'. A few examples should make clear how the function works. It is assumed that all the following pieces of code are executed in a program which uses the USA locale (`en_US'). The simplest form of the format is this: strfmon (buf, 100, "@%n@%n@%n@", 123.45, -567.89, 12345.678); The output produced is "@$123.45@-$567.89@$12,345.68@" We can notice several things here. First, the widths of the output numbers are different. We have not specified a width in the format string, and so this is no wonder. Second, the third number is printed using thousands separators. The thousands separator for the `en_US' locale is a comma. The number is also rounded. .678 is rounded to .68 since the format does not specify a precision and the default value in the locale is 2. Finally, note that the national currency symbol is printed since `%n' was used, not `i'. The next example shows how we can align the output. strfmon (buf, 100, "@%=*11n@%=*11n@%=*11n@", 123.45, -567.89, 12345.678); The output this time is: "@ $123.45@ -$567.89@ $12,345.68@" Two things stand out. Firstly, all fields have the same width (eleven characters) since this is the width given in the format and since no number required more characters to be printed. The second important point is that the fill character is not used. This is correct since the white space was not used to achieve a precision given by a `#' modifier, but instead to fill to the given width. The difference becomes obvious if we now add a width specification. strfmon (buf, 100, "@%=*11#5n@%=*11#5n@%=*11#5n@", 123.45, -567.89, 12345.678); The output is "@ $***123.45@-$***567.89@ $12,456.68@" Here we can see that all the currency symbols are now aligned, and that the space between the currency sign and the number is filled with the selected fill character. Note that although the width is selected to be 5 and 123.45 has three digits left of the decimal point, the space is filled with three asterisks. This is correct since, as explained above, the width does not include the positions used to store thousands separators. One last example should explain the remaining functionality. strfmon (buf, 100, "@%=0(16#5.3i@%=0(16#5.3i@%=0(16#5.3i@", 123.45, -567.89, 12345.678); This rather complex format string produces the following output: "@ USD 000123,450 @(USD 000567.890)@ USD 12,345.678 @" The most noticeable change is the alternative way of representing negative numbers. In financial circles this is often done using parentheses, and this is what the `(' flag selected. The fill character is now `0'. Note that this `0' character is not regarded as a numeric zero, and therefore the first and second numbers are not printed using a thousands separator. Since we used the format specifier `i' instead of `n', the international form of the currency symbol is used. This is a four letter string, in this case `"USD "'. The last point is that since the precision right of the decimal point is selected to be three, the first and second numbers are printed with an extra zero at the end and the third number is printed without rounding.  File: libc.info, Node: Yes-or-No Questions, Prev: Formatting Numbers, Up: Locales Yes-or-No Questions =================== Some non GUI programs ask a yes-or-no question. If the messages (especially the questions) are translated into foreign languages, be sure that you localize the answers too. It would be very bad habit to ask a question in one language and request the answer in another, often English. The GNU C library contains `rpmatch' to give applications easy access to the corresponding locale definitions. - Function: int rpmatch (const char *RESPONSE) The function `rpmatch' checks the string in RESPONSE whether or not it is a correct yes-or-no answer and if yes, which one. The check uses the `YESEXPR' and `NOEXPR' data in the `LC_MESSAGES' category of the currently selected locale. The return value is as follows: `1' The user entered an affirmative answer. `0' The user entered a negative answer. `-1' The answer matched neither the `YESEXPR' nor the `NOEXPR' regular expression. This function is not standardized but available beside in GNU libc at least also in the IBM AIX library. This function would normally be used like this: ... /* Use a safe default. */ _Bool doit = false; fputs (gettext ("Do you really want to do this? "), stdout); fflush (stdout); /* Prepare the `getline' call. */ line = NULL; len = 0; while (getline (&line, &len, stdout) >= 0) { /* Check the response. */ int res = rpmatch (line); if (res >= 0) { /* We got a definitive answer. */ if (res > 0) doit = true; break; } } /* Free what `getline' allocated. */ free (line); Note that the loop continues until an read error is detected or until a definitive (positive or negative) answer is read.  File: libc.info, Node: Message Translation, Next: Searching and Sorting, Prev: Locales, Up: Top Message Translation ******************* The program's interface with the human should be designed in a way to ease the human the task. One of the possibilities is to use messages in whatever language the user prefers. Printing messages in different languages can be implemented in different ways. One could add all the different languages in the source code and add among the variants every time a message has to be printed. This is certainly no good solution since extending the set of languages is difficult (the code must be changed) and the code itself can become really big with dozens of message sets. A better solution is to keep the message sets for each language are kept in separate files which are loaded at runtime depending on the language selection of the user. The GNU C Library provides two different sets of functions to support message translation. The problem is that neither of the interfaces is officially defined by the POSIX standard. The `catgets' family of functions is defined in the X/Open standard but this is derived from industry decisions and therefore not necessarily based on reasonable decisions. As mentioned above the message catalog handling provides easy extendibility by using external data files which contain the message translations. I.e., these files contain for each of the messages used in the program a translation for the appropriate language. So the tasks of the message handling functions are * locate the external data file with the appropriate translations. * load the data and make it possible to address the messages * map a given key to the translated message The two approaches mainly differ in the implementation of this last step. The design decisions made for this influences the whole rest. * Menu: * Message catalogs a la X/Open:: The `catgets' family of functions. * The Uniforum approach:: The `gettext' family of functions.  File: libc.info, Node: Message catalogs a la X/Open, Next: The Uniforum approach, Up: Message Translation X/Open Message Catalog Handling =============================== The `catgets' functions are based on the simple scheme: Associate every message to translate in the source code with a unique identifier. To retrieve a message from a catalog file solely the identifier is used. This means for the author of the program that s/he will have to make sure the meaning of the identifier in the program code and in the message catalogs are always the same. Before a message can be translated the catalog file must be located. The user of the program must be able to guide the responsible function to find whatever catalog the user wants. This is separated from what the programmer had in mind. All the types, constants and functions for the `catgets' functions are defined/declared in the `nl_types.h' header file. * Menu: * The catgets Functions:: The `catgets' function family. * The message catalog files:: Format of the message catalog files. * The gencat program:: How to generate message catalogs files which can be used by the functions. * Common Usage:: How to use the `catgets' interface.