feof

feof is a function in the C standard library used to test whether the end-of-file indicator for a given FILE stream has been set. It is declared in stdio.h and has the prototype int feof(FILE *stream). The function returns a nonzero value if the end-of-file indicator for the stream is set, and zero otherwise.

The end-of-file indicator is set by input functions when an attempt to read reaches the end of the underlying file. Once the indicator is set, feof will report true for that stream until the indicator is cleared. The indicator can be cleared by clearerr or by repositioning the stream with functions such as fseek, fsetpos, or rewind.

Usage and caveats: feof should not be used as the primary loop condition to control input. It only reports whether an end-of-file condition has already been encountered by a prior read operation. A common pattern is to check the return value of the input function (for example, fgets, fread, fgetc) and, when it indicates end-of-file or error, then consult feof to determine whether end-of-file caused the condition, or ferror to check for a read error.

Relation to other status checks: feof complements ferror, which tests for read errors. Together, they help distinguish among end-of-file, error, and successful reads when processing streams.

Overall, feof provides a way to query whether the end of a stream has already been reached, rather than predicting future data availability.