c Programming/C Reference/stdio.h/perror

The POSIX error function, perror, is used in C and C++ to print an error message to stderr, based on the error state stored in errno.It prints str and an implementation-defined error message corresponding to the global variable errno.

History

The definition of perror was first released in Issue 1 of the System V Interface Definition.

Usage

Inclusion

#include <stdio.h>

Declaration

void perror(const char* prefix);

Example

int fd = open("/etc/passwd", O_RDONLY);
if (fd == -1) {
    perror("open");
    exit(1); 
}

Semantics

If the parameter prefix is non-NULL, perror will first print prefix followed by a colon and a space to standard error. Then, it will print the result of strerror to standard error, followed by a newline character. For instance the above example may print

open: Permission denied

See also

• errno
• strerror
• POSIX
• Single UNIX Specification
• System V Interface Definition

External links

• C++ reference for std::perror