Question

In various examples found on the web fgetc() is used like this:

FILE *fp = fopen(PATH, "r");

if (fp == NULL) {
    perror("main");
    exit(EXIT_FAILURE);
}

int ch;

while (ch = fgetc(fp) != EOF) {
    // do something
}

But according to the manpage to fgetc()

If a read error occurs, the error
indicator for the stream shall be set,
fgetc() shall return EOF, [CX] and
shall set errno to indicate the error.

So need I check this too? And how?

Answer 1

You can check it with ferror(3), right after the while:

while (EOF != (ch = fgetc(fp)))
   // do something

if (ferror(fp) != 0)
   // error handling

ferror returns a non-zero if an error occured.

If you want use fp after an error occured, you’ll need to clear the error flag with clearerr:

clearerr(fp);