_ungetch, _ungetwch, _ungetch_nolock, _ungetwch_nolock

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06/05/2017

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The latest version of this topic can be found at _ungetch, _ungetwch, _ungetch_nolock, _ungetwch_nolock.

Pushes back the last character that's read from the console.

Important

This API cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported with /ZW.

Syntax

int _ungetch(  
   int c   
);  
wint_t _ungetwch(  
   wint_t c   
);  
int _ungetch_nolock(  
   int c   
);  
wint_t _ungetwch_nolock(  
   wint_t c   
);

Parameters

c
Character to be pushed.

Return Value

Both functions return the character c if successful. If there is an error, _ungetch returns a value of EOF and _ungetwchreturnsWEOF.

Remarks

These functions push the character c back to the console, causing c to be the next character read by _getch or _getche (or_getwch or_getwche). _ungetch and _ungetwch fail if they are called more than once before the next read. The c argument may not be EOF (or WEOF).

The versions with the _nolock suffix are identical except that they are not protected from interference by other threads. They may be faster since they do not incur the overhead of locking out other threads. Use these functions only in thread-safe contexts such as single-threaded applications or where the calling scope already handles thread isolation.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_ungettch`	`_ungetch`	`_ungetch`	`_ungetwch`
`_ungettch_nolock`	`_ungetch_nolock`	`_ungetch_nolock`	`_ungetwch_nolock`

Requirements

Routine	Required header
`_ungetch`, `_ungetch_nolock`	<conio.h>
`_ungetwch`, `_ungetwch_nolock`	<conio.h> or <wchar.h>

For additional compatibility information, see Compatibility.

Example

// crt_ungetch.c  
// compile with: /c  
// In this program, a white-space delimited   
// token is read from the keyboard. When the program   
// encounters a delimiter, it uses _ungetch to replace   
// the character in the keyboard buffer.  
//  
  
#include <conio.h>  
#include <ctype.h>  
#include <stdio.h>  
  
int main( void )  
{  
   char buffer[100];  
   int count = 0;  
   int ch;  
  
   ch = _getche();  
   while( isspace( ch ) )      // Skip preceding white space.  
      ch = _getche();  
   while( count < 99 )         // Gather token.  
   {  
      if( isspace( ch ) )      // End of token.  
         break;  
      buffer[count++] = (char)ch;  
      ch = _getche();  
   }  
   _ungetch( ch );            // Put back delimiter.  
   buffer[count] = '\0';      // Null terminate the token.  
   printf( "\ntoken = %s\n", buffer );  
}

Whitetoken = White

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