setlocale
- C course
- Advanced
- Lesson 63/83
- 5 min
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.
Practice 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.
Starter code
#include <stdio.h>
#include <locale.h>
// Set the locale to 'C' and print the returned name
int main(void) {
return 0;
}Sample solution
#include <stdio.h>
#include <locale.h>
int main(void) {
char *loc = setlocale(LC_ALL, "C");
printf("yerel: %s\n", loc);
return 0;
}Expected output
yerel: C
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 setlocale call
char *loc = setlocale(____, "C");char *loc = setlocale(LC_ALL, "C");Explanation: LC_ALL sets all categories at once.
2 Match locale categories
| Term | Meaning |
|---|---|
LC_ALL |
All categories |
LC_CTYPE |
Character class |
LC_TIME |
Date format |
LC_NUMERIC |
Number format |
3 What does setlocale(LC_ALL, "C") return?
- NULL
- 0
- The string "C" Correct answer
- "tr_TR"
Explanation: On success it returns the "C" locale name.