C <stdio.h> - ferror() Function

The C <stdio.h> ferror() function is used to check if the error indicator associated with the file stream is set. It returns a non-zero value if it is set, else returns 0.

The error indicator are generally set by a previous failed operation on the stream, and gets cleared by calling function like clearerr, rewind or freopen.

Syntax

int ferror ( FILE * stream );

Parameters

Return Value

Returns non-zero value if the error indicator associated with the file stream is set, else returns 0.

Example:

Lets assume that we have a file called test.txt. In the example below, file is opened in read-only mode. The program tries to write a character in this file. As the file is opened in read-only mode, an error is generated which is detected by ferror() function.

#include <stdio.h>
 
int main (){
  //open the file in read mode
  FILE *pFile = fopen("test.txt", "r");
  
  //write a character in the file
  fputc('A', pFile);
  
  //error is detected
  if(ferror(pFile))
    printf("Some error has occurred.");
  
  //close the file
  fclose(pFile);
  return 0;
}

The output of the above code will be:

Some error has occurred.