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Controls stream buffering. This function is deprecated; use setvbuf instead.

void setbuf(
   FILE *stream,
   char *buffer 


Pointer to FILE structure.


User-allocated buffer.

The setbuf function controls buffering for stream. The stream argument must refer to an open file that has not been read or written. If the buffer argument is NULL, the stream is un-buffered. If not, the buffer must point to a character array of length BUFSIZ, where BUFSIZ is the buffer size as defined in STDIO.H. The user-specified buffer, instead of the default system-allocated buffer for the given stream, is used for I/O buffering. The stderr stream is un-buffered by default, but you can use setbuf to assign buffers to stderr.

setbuf has been replaced by setvbuf, which is the preferred routine for new code. setbuf is retained for compatibility with existing code.


Required header



For additional compatibility information, see Compatibility in the Introduction.

// crt_setbuf.c
// compile with: /W3
// This program first opens files named DATA1 and
// DATA2. Then it uses setbuf to give DATA1 a user-assigned
// buffer and to change DATA2 so that it has no buffer.
#include <stdio.h>

int main( void )
   char buf[BUFSIZ];
   FILE *stream1, *stream2;

   fopen_s( &stream1, "data1", "a" );
   fopen_s( &stream2, "data2", "w" );

   if( (stream1 != NULL) && (stream2 != NULL) )
      // "stream1" uses user-assigned buffer:
      setbuf( stream1, buf ); // C4996
      // Note: setbuf is deprecated; consider using setvbuf instead
      printf( "stream1 set to user-defined buffer at: %Fp\n", buf );

      // "stream2" is unbuffered
      setbuf( stream2, NULL ); // C4996
      printf( "stream2 buffering disabled\n" );
stream1 set to user-defined buffer at: 0012FCDC stream2 buffering disabled

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.