One of the primary functions of most computer programs is to manipulate data, some or all of which may involve interaction between the program and a computer user. In commercial situations, it is important that such interactions take place in the native language of each user. Cultural data should also observe the correct customs.

When you write programs to support multilanguage operation, you must also consider the fact that languages can be represented within the computer system by one or more codesets. Because of the requirements of different languages, characters in codesets may vary in both size (8-bit, 16-bit, and so on) and binary representation.

You can satisfy the preceding requirements by writing programs that make no hard-coded assumptions about language, cultural data, or character encodings. Such programs are said to be internationalized. Data specific to each supported language, territory, and codeset combination are held separately from the program code and can be bound to the run-time environment by language-initialization functions.

Digital UNIX provides the following facilities for developing internationalized software, defining localization data, and announcing specific language requirements:

• Library functions that handle extended character codes and that provide language- and codeset-independent character classification, case conversion, number format conversion, and string collation

• Library functions that let programs determine cultural and language-specific data dynamically

• A message system that allows program messages to be held apart from the program code, translated into different languages, and retrieved by a program at run time

• An initialization function that binds a program at run time to the specified language requirements of each user

The rest of this chapter describes each of the these facilities in more detail.

if ((c = getchar()) == \141)

This condition assumes that lowercase a is always represented by a fixed octal value, which may not be true for all codesets. The following statement represents an improvement in that it substitutes a character constant for the octal value:

if ((c = getchar()) == 'a')

1. Declares a pointer to schar as char.

2. Declares the variable wchar to be of type wchar_t.

3. Calls the catgets() function to retrieve the value of MSG_ID from the message catalog for the user's locale.

   The catgets() function returns a value as an array of bytes so the value is returned to the schar variable. If the accented character is not available in the locale's codeset, the test is made against the unaccented base character (a).

4. Because the locale's codeset may contain multibyte characters, tests to make sure the value contained in schar represents a valid multibyte character; if yes, converts it to a wide-character value and stores the results in the variable wchar.

   If schar does not contain a valid multibyte character, signals an error.

5. Codes the conditional statement to include the value contained in wchar as the constant.

a_var |= 0x20;

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a_var &= 0xdf;

The preceding statements are not safe to use in internationalized programs because they:

• Assume ASCII-coded character values

• Do not check for valid input

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int cmp_val;
char *s1;
char *s2;

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cmp_val = strcmp(s1, s2);

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• Codeset name

• Date and time formats

• Names of the days of the week

• Names of the months of the year

• Abbreviations for names of days

• Abbreviations for names of months

• Radix character

• Thousands separator character

• Affirmative and negative responses for yes/no queries

• Currency symbol and its position within a currency value

• Emperor/Era name and year (for Japanese locales)

nl_langinfo(D_T_FMT);

1. Binds the program at run time to the locale set for the system or individual user.

2. Calls the time() subroutine to return the time value, relative to Coordinated Universal Time, to the clock variable.

3. Calls the localtime() function to convert the value contained in clock to a value that can be stored in a tm structure, whose members represent values for year, month, day, hour, minute, and so forth.

4. Calls strftime() to generate a date string formatted as defined in the user's locale from the value contained in the tm structure.

   The buf argument is a pointer to a string variable in which the date string is returned. The size argument contains the maximum size of buf. The "%x" argument specifies conversion specifications, similar to the format strings used with the printf() and scanf() functions. The "%x" argument is replaced in the output string by representation appropriate for the locale.

5. Calls the puts() function to copy the string contained in buf to the standard output stream (stdout) and to append a newline character.

strfmon(buf, size, "%n", value);  (1)

1. This statement formats the double-precision floating-point value contained in the variable value. The argument "%n" is the format specification that is replaced by the format defined in the run-time locale. The results are returned to the array buf, whose maximum length is contained in the variable size.

The money program demonstrates how the strfmon() function works. The source file for this sample program is available in the /usr/i18n/examples/money directory.

struct lconv *app_conv;

You can use the following features, which are contained in the structure lconv, in program-defined routines:

• Radix character

• Thousands separator character

• Digit grouping size

• International currency symbol

• Local currency symbol

• Radix character for monetary values

• Thousands separator for monetary values

• Digit grouping size for monetary values

• Positive sign

• Negative sign

• Number of fractional digits to be displayed

• Parenthesis symbols for negative monetary values

• The way program messages are defined and accessed

• How the program presents output text

• How the program processes input text

These considerations are discussed in the following sections.

The category argument can be one of the following:

• LC_ALL to use, change, or query all portions of the user's locale

• LC_CTYPE to use, change, or query the portion of the user's locale that classifies characters

• LC_COLLATE to use, change, or query the portion of the user's locale that specifies character collation order

• LC_MESSAGES to use, change, or query the portion of the user's locale that specifies yes/no responses and program messages

• LC_MONETARY to use, change, or query the portion of the user's locale that specifies special characters used in monetary values

• LC_NUMERIC to use, change, or query the portion of the user's locale that specifies the characters used for decimal point and thousands separator

• LC_TIME to use, change, or query the portion of the user's locale that specifies names and abbreviations for days of the week and months of the year, and other strings and formatting conventions that govern expressions of date and time

setlocale(LC_ALL, "");

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nl_catd catd;  (1)
char buf[BUFSIZ];  (2)

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setlocale(LC_ALL, );  (3)
catd = catopen(CAT_NAME, 0);  (4)

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printf(catgets(catd, NL_SETD, LOCALE_PROMPT_MSG,
               "Enter locale name: "));      (5)
gets(buf);  (6)
setlocale(LC_ALL, buf);  (7)

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1. Declares a catalog descriptor catd as type nl_catd.

2. Declares the buf variable into which the locale name will later be stored.

   To make sure that the variable is large enough to accommodate locale names on different systems, you should set its maximum size to the constant BUFSIZ, which is defined by the system vendor in /usr/include/stdio.h.

3. Calls setlocale() to initialize the program's locale settings to those in effect for the user who runs the program.

4. Calls catopen() to open the message catalog that contains the program's messages; returns the catalog's descriptor to the catd variable.

   The CAT_NAME constant is defined in the program's own header file.

5. Prompts the user for a new locale name.

   The NL_SETD constant specifies the default message set number in a message catalog and is defined in /usr/include/nl_types.h. The identifier LOCALE_PROMPT_MSG specifies the prompt string translation in the default message set.

6. Calls the gets() function to read the locale name typed by the user into the buf variable.

7. Calls setlocale() with buf as the locale_name argument to reinitialize all portions of the locale.