| Standards / Extensions | C or C++ | Dependencies |
|---|---|---|
ISO C |
both |
#include <stdio.h>
void setbuf(FILE *__restrict__stream, char *__restrict__buffer);Controls buffering for the specified stream. The stream pointer must refer to an open file, and setbuf() must be the first operation on the stream.
If the buffer argument is NULL, the stream is unbuffered. If not, the buffering mode will be full buffer and the buffer must point to a character array of length at least BUFSIZ, which is the buffer size defined in the stdio.h header file. I/O functions use the buffer, which you specify here, for input/output buffering instead of the default system-allocated buffer for the given stream. If the buffer does not meet the requirements of the z/OS® XL C/C++ product, the buffer is not used.
The setvbuf() function is more flexible than setbuf(), because you can specify the type of buffering and size of buffer.
For example, if the buffer is an automatic array (block scope) and is associated with the stream s, leaving the block causes the storage to be deallocated. I/O operations of stream s are prevented from using deallocated storage. Any operation on s would fail because the operation would attempt to access the nonexistent storage.
To ensure that the buffer is available throughout the life of a program, make the buffer a variable allocated at file scope. This can be achieved by using an identifier of type array declared at file scope, or by allocating storage (with malloc() or calloc()) and assigning the storage address to a pointer declared at file scope.
VSAM file types do not support unbuffered I/O, causing requests for unbuffered I/O to fail.
setbuf() returns no values.
For details about errno values, and about buffers you may have set, see discussions about buffering in z/OS XL C/C++ Programming Guide.
⁄* CELEBS01
This example opens the file myfile.dat for writing.
It then calls the &setbuf. function to establish a buffer of
length BUFSIZ.
When string is written to the stream, the buffer buf is used
and contains the string before it is flushed to the file.
*⁄
#include <stdio.h>
int main(void)
{
char buf[BUFSIZ];
char string[] = "hello world";
FILE *stream;
stream = fopen("myfile.dat", "wb,recfm=f");
setbuf(stream,buf); ⁄* set up buffer *⁄
fwrite(string, sizeof(string), 1, stream);
printf("%s\n",buf); ⁄* string is found in buf now *⁄
fclose(stream); ⁄* buffer is flushed out to myfile.dat *⁄
}