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setvbuf

Usage

   #include <stdio.h>
   int setvbuf(FILE *fp,char *buf, int mode,size_t size);

   ANSI

Description

   setvbuf specifies the type and size of a buffer to be used for a stream.
   In addition to the function parameters the following global variable
   affects the behaviour of this function: _okbigbuf.

   This is used only in the T, S and M memory models under MS-DOS and the S
   and M memory models under OS/2, and controls how buffers are allocated
   when buf is NULL. It is statically initialized to 0 or 1 by the
   programmer (the default definition in the library sets it to 1). If
   _okbigbuf is 1 and the memory model is T, S or M: setvbuf tries to
   allocate a buffer outside of the data segment. If that fails, and size <=
   BUFSIZ, then setvbuf tries to allocate a buffer within the data segment.

   A buffer that is outside the data segment is marked by setting _IOBIGBUF
   in fp->_flags . If _okbigbuf is 0 or the memory model is C or L: setvbuf
   tries to allocate a buffer within the data segment. A buffer allocated by
   setvbuf is flagged by _IOMYBUF being set in fp->_flags.

   The function parameters are:

   fp       Stream pointer that is already opened, but before any
            reads or writes have been done to the stream.

   buf      Pointer to buffer, or NULL. If NULL, then setvbuf uses
            malloc or faralloc to try to allocate a buffer of size

            bytes. If buf is not NULL, it points to a buffer that
            setvbuf will cause to be associated with the stream fp.

   mode     Is one of:

            _IONBF           No buffering. The buf and size parameters are
                             ignored. Unbuffered I/O means that:
                             data written is immediately passed on
                             to DOS. When data is read, exactly
                             enough is read.

            _IOLBF           Do line buffering. The actual I/O is performed
                             when a newline is read or written.

            _IOFBF           Full buffering. Data is read a full buffer
                             at a time. Data is written only when the
                             buffer is full.


   size     If buf is NULL, then size is the number of bytes to allocate
            for the buffer. If buf is not NULL, then size must be
            the number of bytes in the buffer points to.


Example 

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

   int main(int argc,char *argv[])
   {
       FILE *fp;
       static char buf[100];
           /* Make stdprn unbuffered */
       setvbuf(stdprn,NULL,_IONBF,0);
       fprintf(stdprn,"unbuffered\n");
       if (argc == 2)          /* if an argument */
           fp = fopen(argv[1],"w");
       else
           fp = stdout;        /* use standard output */

       if (setvbuf(fp,buf,_IOLBF,sizeof(buf))) {
           printf("setvbuf failed\n");
           return EXIT_FAILURE;
       }
       else
       {
           fprintf(fp,"This is going to fp\n");
           fclose(fp);
       }
       return EXIT_SUCCESS;
   }

Return Value

   If success, the various fields that fp points to are updated to show the
   buffer and 0 is returned. If there is insufficient memory for the buffer
   or the mode parameter is invalid, a non-zero result is returned

See Also

   setbuf