#include <stdio.h>

void perror(const char *s);


Partially implemented


IEEE Std 1003.1-2017


The perror() function shall map the error number accessed through the symbol errno to a language-dependent error message, which shall be written to the standard error stream as follows:

  • First (if s is not a null pointer and the character pointed to by s is not the null byte), the string pointed to by s followed by a <colon> and a <space>.

  • Then an error message string followed by a <newline>.

The contents of the error message strings shall be the same as those returned by strerror() with argument errno. The perror() function shall mark for update the last data modification and last file status change timestamps of the file associated with the standard error stream at some time between its successful completion and exit(), abort(), or the completion of fflush() or fclose() on stderr.

The perror() function shall not change the orientation of the standard error stream.

On error, perror() shall set the error indicator for the stream to which stderr points, and shall set errno to indicate the error.

Since no value is returned, an application wishing to check for error situations should call clearerr(stderr) before calling perror(), then if ferror(stderr) returns non-zero, the value of errno indicates which error occurred.

Return value

The perror() function shall not return a value.


Refer to fputc().



Known bugs


See Also

  1. Standard library functions
  2. Table of Contents