ungetc

 

C

Language

Standard Library

Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

Algorithms

Numerics

Input/output support

Localization support

Thread support (C11)

Atomic operations (C11)

 

File input/output

Functions
File access
fopen freopen fclose fflush	fwide setbuf setvbuf
Direct input/output
fread
fwrite
Unformatted input/output
fgetc fgets fputc fputs getchar gets putchar puts ungetc	fgetwc fgetws fputwc fputws getwchar putwchar ungetwc
Formatted input/output
scanffscanfsscanf vscanfvfscanfvsscanf (C99)(C99)(C99) printffprintfsprintfsnprintf (C99) vprintfvfprintfvsprintfvsnprintf (C99)	wscanffwscanfswscanf vwscanfvfwscanfvswscanf (C99)(C99)(C99) wprintffwprintfswprintf vwprintfvfwprintfvswprintf
File positioning
ftell
fgetpos
fseek
fsetpos
rewind
Error handling
clearerr
feof
ferror
perror
Operations on files
remove
rename
tmpfile
tmpnam

 

Defined in header <stdio.h>
int ungetc( int ch, FILE *stream );

Puts the character ch back to the given file stream.

Parameters

ch	-	character to be put back
stream	-	file stream to put the character back to

Return value

On success ch is returned.

On failure EOF is returned and the given stream remains unchanged.

Example

ungetc with error checking

Run this code

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    FILE* fp = fopen("test.txt", "w");
    fputs("abc\n", fp);
    fclose(fp);
    fp = fopen("test.txt", "r");
 
    /* Read  "abc".  */
    /* Write "abbc". */
    char ch;
    int ret_code;
    ch=fgetc(fp);   /* read 'a' */
    putchar(ch);
    ch=fgetc(fp);   /* read 'b' */
    putchar(ch);
 
    ret_code = ungetc(ch,fp);   /* push 'b' back to input file */
    /* Test whether EOF was reached. */
    if (ret_code == EOF)
       if (ferror(fp)) 
       {
          perror("ungetc()");
          fprintf(stderr,"ungetc() failed in file %s at line # %d\n", __FILE__,__LINE__-6);
          exit(EXIT_FAILURE);
       }
 
    ch=fgetc(fp);   /* reread 'b' */
    putchar(ch);
    ch=fgetc(fp);   /* read 'c'   */
    putchar(ch);
 
    return EXIT_SUCCESS;
}

Output:

abbc

See also

fgetcgetc	gets a character from a file stream (function)
C++ documentation for ungetc