# std::strerror

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< cpp‎ | string‎ | byte

Defined in header `<cstring>` |  |
char* strerror( int errnum ); |  |

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

errnum is usually acquired from the `errno` variable, however the function accepts any value of type int. The contents of the string are locale-specific.

The returned string must not be modified by the program, but may be overwritten by a subsequent call to the `strerror` function. `strerror` is not required to be thread-safe. Implementations may be returning different pointers to static read-only string literals or may be returning the same pointer over and over, pointing at a static buffer in which `strerror` places the string.

### Parameters

errnum | - | integral value referring to an error code

### Return value

Pointer to a null-terminated byte string corresponding to the errno error code errnum.

### 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.

POSIX has a thread-safe version called `strerror_r` defined. Glibc defines an incompatible version.

### Example

Run this code

    #include <cerrno>
    #include <clocale>
    #include <cmath>
    #include <cstring>
    #include <iostream>

    int main()
    {
        const double not_a_number = std::log(-1.0);
        std::cout << not_a_number << '\n';

        if (errno == EDOM)
        {
            std::cout << "log(-1) failed: " << std::strerror(errno) << '\n';
            std::setlocale(LC_MESSAGES, "de_DE.utf8");
            std::cout << "Or, in German, " << std::strerror(errno) << '\n';
        }
    }

Possible output:

    nan
    log(-1) failed: Numerical argument out of domain
    Or, in German, Das numerische Argument ist ausserhalb des Definitionsbereiches

### See also

perror | displays a character string corresponding of the current error to stderr (function)
E2BIG, EACCES, ..., EXDEV | macros for standard POSIX-compatible error conditions (macro constant)

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