UNGETC(3) Library Functions Manual UNGETC(3)

ungetc — push byte back into input stream

#include <stdio.h>

int ungetc(int c, FILE *stream);

The ungetc() function pushes the byte specified by c (converted to an unsigned char ) back onto the input stream pointed to by stream . The pushed-back bytes will be returned by subsequent reads on that stream in the reverse order of their pushing. A successful intervening call (with the stream pointed to by stream ) to a file-positioning function (.Fn fseek , fsetpos(3) or rewind(3) ) discards any pushed-back bytes for the stream. The external storage corresponding to the stream is unchanged.

One byte of push-back is guaranteed. If ungetc() is called too many times on the same stream without an intervening read or file-positioning operation on that stream, the operation may fail.

If the value of equals that of the macro EOF, the operation fails and the input stream is unchanged.

A successful call to ungetc() clears the end-of-file indicator for the stream. The value of the file-position indicator for the stream after reading or discarding all pushed-back bytes will be the same as it was before the bytes were pushed back. The file-position indicator is decremented by each successful call to ungetc(); if its value was 0 before a call, its value is indeterminate after the call.

Upon successful completion, ungetc() returns the byte pushed back after conversion. Otherwise it returns EOF.

No errors are defined.

None.

None.

None.

fseek(3) , getc(3) , fsetpos(3) , read(3) , rewind(3) , setbuf(3) , <stdio.h> .

Derived from Issue 1 of the SVID.

February 1997 posix.fail