locale.md

locale.h - Localization

Category: 📂 std/ (C Standard Library)
Header: <locale.h>
Scope: C89, C99, C11

The locale.h header defines structures and functions for controlling various locale-specific settings.

Facilities Overview

Facility Category	Key Symbols	Description
Locale Control	setlocale	Setting or querying the current locale.
Formatting Info	localeconv	Retrieving formatting details for the current locale.
Constants	LC_ALL, LC_NUMERIC, LC_TIME	Category selectors for setlocale.

---

Types & Variables

struct lconv

Significant fields include:

• decimal_point: Character used for decimal point.
• thousands_sep: Character used for thousands separator.
• currency_symbol: Local currency symbol.
• int_curr_symbol: International currency symbol.

Example

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

int main(void) {
    struct lconv *lc = localeconv();
    printf("Decimal point: '%s'\n", lc->decimal_point);
    return 0;
}

---

Functions

Locale Control

setlocale

char *setlocale(int category, const char *locale)

Sets or queries the program's current locale.

• category: LC_ALL, LC_COLLATE, LC_CTYPE, LC_MONETARY, LC_NUMERIC, LC_TIME.
• locale: e.g., "C" (default), "" (system default), "en_US.UTF-8".

Returns: A string pointer to the locale name associated with the category, or NULL if the request cannot be honored.

Example

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

int main(void) {
    // Attempt to set to system default
    char *res = setlocale(LC_ALL, "");
    
    if (res == NULL) {
        fprintf(stderr, "Failed to set system locale. Fallback to C.\n");
        // setlocale failure usually leaves locale unchanged (C)
    } else {
        printf("Locale set to: %s\n", res);
    }
    return 0;
}

Formatting Info

localeconv

struct lconv *localeconv(void)

Returns a pointer to a struct lconv that contains details about numeric and monetary formatting.