how to detect a file is opened or not in c

Question

I\'m trying to output some string on a txt file by using c program

however, I need to see if the I have the permission to write on the txt file, if not, I need to pr

Answer 1

You can do some error checking to see if the calls to fopen and fprintf succeeded.

fopen's return value is the pointer to the file object on success and a NULL pointer on failure. You could check for NULL return value.

FILE *file = fopen("text.txt", "a");

if (file == NULL) {
     perror("Error opening file: ");
}

Similarly fprintf return a negative number on error. You could do a if(fprintf() < 1) check.