std::strerror(3)

💖 std::strerror 💖

Okay bestie, this is the std::strerror page from the C++ Standard Libary manual — yes, the manual-name situation is folded up here near the top so we can get straight to the good stuff. ✨

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✨ NAME ✨

std::strerror — std::strerror. That’s the name, no cap, it’s giving “function named exactly after itself” energy. 🎀

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🦋 Synopsis 🦋

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.

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💅 Parameters 💅

• errnum — integer value referring to an error code.

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🎀 Return value 🎀

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

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🧚 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. Incompatible is the key word there, bestie. 👀

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🌸 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

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👑 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).
• C documentation for strerror — the C side of the lore. 🫶

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And that’s the whole page, bestie! Source/version/date tea: http://cppreference.com, 2024.06.10, and this manual page is std::strerror(3). Mwah 💋✨