strerror, strerror_s, strerrorlen_s

Header: <string.h>

  1. Returns a pointer to the textual description of the system error code errnum, identical to the description that would be printed by perror().

# Declarations

char* strerror( int errnum );

errno_t strerror_s( char *buf, rsize_t bufsz, errno_t errnum );

(since C11)

size_t strerrorlen_s( errno_t errnum );

(since C11)

# Parameters

# Notes

POSIX allows subsequent calls to strerror to invalidate the pointer value returned by an earlier call. It also specifies that it is the LC_MESSAGES locale facet that controls the contents of these messages.

strerror_s is the only bounds-checked function that allows truncation, because providing as much information as possible about a failure was deemed to be more desirable. POSIX also defines strerror_r for similar purposes.

# Example

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <locale.h>
 
int main(void)
{
    FILE *fp = fopen(tmpnam((char[L_tmpnam]){0}), "r");
    if(fp==NULL) {
        printf("File opening error: %s\n", strerror(errno));
        setlocale(LC_MESSAGES, "de_DE.utf8");
        printf("Now in German: %s\n", strerror(errno));
#ifdef __STDC_LIB_EXT1__
        setlocale(LC_ALL, "ja_JP.utf8"); // printf needs CTYPE for multibyte output
        size_t errmsglen = strerrorlen_s(errno) + 1;
        char errmsg[errmsglen]; 
        strerror_s(errmsg, errmsglen, errno);
        printf("Now in Japanese: %s\n", errmsg);
#endif
    }
}

# See also