c - Is it possible to distinguish the error returned by fgets

Question

Upon looking at the ISO C11 standard for fgets §7.21.7.2, 3, the return value is stated regarding the synopsis code:

#include <stdio.h>
char *fgets(char* restrict s, int n, FILE* restrict stream);

The fgets function returns s if successful. If end-of-file is encountered and no characters have been read into the array, the contents of the array remain unchanged and a null pointer is returned. If a read error occurs during the operation, the array contents are indeterminate and a null pointer is returned.

The standard says that a null pointer is returned for either an end-of-file and no characters have been read in or a read error occurs. My question is, just from fgets, and the returned null pointer, is there a way to distinguish which of the two cases caused the error?

Answer 1

If the failure has been caused by end-of-file condition, additionally sets the eof indicator (see feof()) on stream. The contents of the array pointed to by str are not altered in this case. If the failure has been caused by some other error, sets the error indicator (see ferror()) on stream. The contents of the array pointed to by str are indeterminate (it may not even be null-terminated).

Therefore, you would need to check for feof() and ferror() in order to determine the error.

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