EOF and Errors - The GNU C Library

Next: Error Recovery, Previous: Formatted Input, Up: I/O on Streams

### 12.15 End-Of-File and Errors

Many of the functions described in this chapter return the value of the macro `EOF` to indicate unsuccessful completion of the operation. Since `EOF` is used to report both end of file and random errors, it's often better to use the `feof` function to check explicitly for end of file and `ferror` to check for errors. These functions check indicators that are part of the internal state of the stream object, indicators set if the appropriate condition was detected by a previous I/O operation on that stream.

— Macro: int EOF

> This macro is an integer value that is returned by a number of narrow stream functions to indicate an end-of-file condition, or some other error situation. With the GNU library, `EOF` is `-1`. In other libraries, its value may be some other negative number.

> This symbol is declared in `stdio.h`.

— Macro: int WEOF

> This macro is an integer value that is returned by a number of wide stream functions to indicate an end-of-file condition, or some other error situation. With the GNU library, `WEOF` is `-1`. In other libraries, its value may be some other negative number.

> This symbol is declared in `wchar.h`.

— Function: int feof (FILE *stream)

> The `feof` function returns nonzero if and only if the end-of-file indicator for the stream stream is set.

> This symbol is declared in `stdio.h`.

— Function: int feof_unlocked (FILE *stream)

> The `feof_unlocked` function is equivalent to the `feof` function except that it does not implicitly lock the stream.

> This function is a GNU extension.

> This symbol is declared in `stdio.h`.

— Function: int ferror (FILE *stream)

> The `ferror` function returns nonzero if and only if the error indicator for the stream stream is set, indicating that an error has occurred on a previous operation on the stream.

> This symbol is declared in `stdio.h`.

— Function: int ferror_unlocked (FILE *stream)

> The `ferror_unlocked` function is equivalent to the `ferror` function except that it does not implicitly lock the stream.

> This function is a GNU extension.

> This symbol is declared in `stdio.h`.

In addition to setting the error indicator associated with the stream, the functions that operate on streams also set `errno` in the same way as the corresponding low-level functions that operate on file descriptors. For example, all of the functions that perform output to a stream—such as `fputc`, `printf`, and `fflush`—are implemented in terms of `write`, and all of the `errno` error conditions defined for `write` are meaningful for these functions. For more information about the descriptor-level I/O functions, see Low-Level I/O.