C++ reference: cstdio: clearerr

clearerr
void clearerr (FILE * stream);

stdio.h

cplusplus.com

Reset error indicators.
Reset error and EOF indicators of the given stream.
After an error occurs using a stream these indicators are not automatically reset to their initial values until this, rewind(), fseek() or fsetpos() functions are called.

Parameters.

stream: pointer to an open file.

Return Value.
None

Example.

/* writing errors */
#include <stdio.h>
main ()
{
  FILE * pFile;
  pFile = fopen("myfile.txt","r");
  if (pFile==NULL) perror ("Error opening file");
  else
  {
    fputc ('x',pFile);
    if (ferror (pFile))
      {
      printf ("Error Writing to myfile.txt\n");
      clearerr (pFile);
      }
    fgetc (pFile);
    if (!ferror (pFile))
      printf ("No errors reading myfile.txt\n"); 
    fclose (pFile);
  }
  return 0;
}

This program opens a existing file called myfile.txt and causes an I/O error. That error is cleared using clearerr so a second error checking returns false.
Output:
Error Writing to myfile.txt No errors reading myfile.txt

See also.
feof, ferror, fwrite