Perror

perror is a standard C library function that reports error conditions by writing to the standard error stream. It is declared in errno.h and relies on the global errno variable to describe the most recent error, usually set by a failing system or library call.

The function prints a human-readable message to stderr. If the argument s is non-null, perror outputs s followed by a colon and a space, then the string associated with errno as produced by strerror(errno). If s is null, only the error message corresponding to errno is printed. Perro does not modify errno; it simply formats and outputs the current error string.

Usage tends to follow a failed system or library call. For example, after attempting to open a file that does not exist, a programmer may call perror("open") to produce a line such as "open: No such file or directory." The exact text depends on the current locale and the specific errno value set by the failing call.

errno codes (such as ENOENT, EACCES, ENFILE) and their corresponding messages are defined by the system and accessible through strerror. Per error handling practices, it is common to call perror immediately after a failing call, and to ensure errno reflects the intended error; in multi-threaded programs, thread-safe variants like strerror_r may be preferred for localization and safety.

Perfor is widely available on POSIX-compliant systems and is often used alongside strerror for broader error reporting. It is a lightweight, convenient way to print concise, human-readable error messages during debugging or user-facing logging.