strerror

Strerror is a C library function that converts an error number into a human-readable string. It is declared in the standard library headers and is commonly used in conjunction with errno to report system or library errors.

The function signature is typically char strerror(int errnum). It returns a pointer to a string describing the error associated with the provided error number. The returned string is usually stored in a static internal buffer, and subsequent calls may overwrite it. The caller should not attempt to free the pointer.

Thread safety and portable variants vary by platform. In POSIX, strerror_r provides a thread-safe alternative by writing the message into a user-supplied buffer; however, there are two main versions with different return conventions depending on the implementation. Some environments also offer strerror_l to select a specific locale. Windows environments provide strerror_s as part of the secure CRT, with different semantics than POSIX variants. Because of these differences, exact behavior can differ between compilers and operating systems.

Locale and portability considerations apply: the language of the message may depend on the current locale, and not all implementations internationalize messages. For robust, portable error reporting, developers may prefer strerror_r or strerror_s, or use higher-level facilities like perror for simple demonstrations, which formats a message based on errno and an optional prefix.

In practice, strerror is suitable for quick debugging and logging when portability is not a concern, but care should be taken about thread safety and buffer ownership in multi-threaded or cross-platform code.