setlocale

Learn locale settings with setlocale.

setlocale

setlocale changes the program's locale; it is defined in <locale.h>. The locale affects character classification, number formatting and date formatting.

setlocale(LC_ALL, "C") selects the minimal locale; it only knows the basic ASCII set. The empty string "" reads from environment variables (LANG, LC_ALL). On success it returns the locale name; on failure it returns NULL. In this lesson we use "C" for deterministic output.

Getting the locale name

When setlocale succeeds it returns the locale name as a string. setlocale(LC_ALL, "C") returns "C" on every system, so the output is deterministic.

The environment locale (empty string) depends on the LANG variable and may differ between test machines. The locale also affects the behavior of mbstowcs and isalpha; so you must call setlocale before multibyte conversion.

Exercise Set the locale and print it

Set the locale with char *loc = setlocale(LC_ALL, "C");. Print the returned name with printf("yerel: %s\n", loc);. Add the <locale.h> header.

Show example solution

#include <stdio.h>
#include <locale.h>

int main(void) {
    char *loc = setlocale(LC_ALL, "C");
    printf("yerel: %s\n", loc);
    return 0;
}

Test yourself

setlocale call

char *loc = setlocale(____, "C");

Show answer

char *loc = setlocale(LC_ALL, "C");

Match locale categories

LC_ALL

All categories
LC_CTYPE

Character class
LC_TIME

Date format
LC_NUMERIC

Number format
What does setlocale(LC_ALL, "C") return?
- NULL
- 0
- The string "C"
- "tr_TR"
Show answer

The string "C" — On success it returns the "C" locale name.

Next lesson: Multibyte conversion

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