ungetc()

Push a character back onto an input stream

Synopsis:

#include <stdio.h>

int ungetc( int c, 
            FILE *fp );

Arguments:

c
The character that you want to push back.
fp
The stream you want to push the character back on.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The ungetc() function pushes the character specified by c back onto the input stream pointed to by fp. This character will be returned the next time that you read from the stream. The pushed-back character is discarded if you call fflush() or a file-positioning function ( fseek() , fsetpos() , or rewind() ) before performing the next read operation.

Only one character (the most recent one) of pushback is guaranteed.

The ungetc() function clears the end-of-file indicator, unless the value of c is EOF.

Returns:

The character pushed back.

Examples:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

int main( void )
  {
    FILE *fp;
    int c;
    long value;

    fp = fopen( "file", "r" );
    value = 0;
    c = fgetc( fp );
    while( isdigit(c) ) {
      value = value*10 + c - '0';
      c = fgetc( fp );
    }
    ungetc( c, fp ); /* put last character back */
    printf( "Value=%ld\n", value );
    fclose( fp );
    return EXIT_SUCCESS;
  }

Classification:

ANSI, POSIX 1003.1

Safety:  
Cancellation point Yes
Interrupt handler No
Signal handler No
Thread Yes

Last modified: 2013-12-23

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