perror() — Print Error Message

Format

#include <stdio.h>
void perror(const char *string);

Language Level: ANSI

Threadsafe: Yes.

Description

The perror() function prints an error message to stderr. If string is not NULL and does not point to a null character, the string pointed to by string is printed to the standard error stream, followed by a colon and a space. The message associated with the value in errno is then printed followed by a new-line character.

To produce accurate results, you should ensure that the perror() function is called immediately after a library function returns with an error; otherwise, subsequent calls might alter the errno value.

Return Value

There is no return value.

The value of errno can be set to:

Value: Meaning
EBADDATA: The message data is not valid.
EBUSY: The record or file is in use.
ENOENT: The file or library cannot be found.
EPERM: Insufficient authorization for access.
ENOREC: Record not found.
EIOERROR: A non-recoverable I/O error occurred.
EIORECERR: A recoverable I/O error occurred.

Example that uses perror()

This example tries to open a stream. If fopen() fails, the example prints a message and ends the program.

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
   FILE *fh;
 
   if ((fh = fopen("mylib/myfile","r")) == NULL)
   {
      perror("Could not open data file");
      abort();
   }
}

Related Information

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