Why does printf return a value?

Question

I know that printf returns a negative error or number of characters printed on success. Only reason to check this return value is if the execution of program s

Answer 1

One of the main reasons why this is used is for troubleshooting. Printf can be used to also write to a file (not only STDOUT). Ensuring that all the charachters have been writen to the file is crucial in some applications. An example of this can be found below:

#include 
#include 

int main(void)
{
  FILE *fp;

  printf("This will display on the screen.\n");

  if((fp=freopen("OUT", "w" ,stdout))==NULL) {
    printf("Cannot open file.\n");
    exit(1);
  }

  if( printf("This will be written to the file OUT.") < 0){
      return -1;
  }

  fclose(fp);

  return 0;
}

You might ask why you should use printf to print a file. Consider this. Some software was developed that had no error logging implemented but instead used printf. A knowledgeable C programmer can redirect the output of printf to a file at the top of the code and thus implement error logging to a file instead of STDOUT. At this point he can use the return value of printf to ensure that the these errors were printed correctly.