setbuf

 

C

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Type support

Dynamic memory management

Error handling

Program utilities

Date and time utilities

Strings library

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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>
void setbuf( FILE          *stream, char          *buffer );		(until C99)
void setbuf( FILE *restrict stream, char *restrict buffer );		(since C99)

Sets the internal buffer to use for stream operations. It should be at least BUFSIZ characters long.

If buffer is not null, equivalent to setvbuf(stream, buffer, _IOFBF, BUFSIZ)

If buffer is null, equivalent to setvbuf(stream, NULL, _IONBF, 0), which turns off buffering.

Parameters

stream	-	the file stream to set the buffer to
buffer	-	pointer to a buffer for the stream to use. If NULL is supplied, the buffering is turned off

Return value

None.

Example

Run this code

#include <stdio.h>
 
int main(void)
{
    int file_size;
    char buffer[BUFSIZ];
    FILE * fp = fopen("test.txt","w+");
    setbuf(fp,buffer);
 
    /* Exhibit the contents of buffer. */
    fputs ("aaa",fp);
    printf("%s\n", buffer);
    fputs ("bbb",fp);
    printf("%s\n", buffer);
    fputs ("ccc",fp);
    printf("%s\n", buffer);
    file_size = ftell(fp);
    printf("file_size = %d\n", file_size);
    fflush (fp);              /* flush buffer */
    printf("%s\n", buffer);
    fputs ("ddd",fp);
    printf("%s\n", buffer);
    fputs ("eee",fp);
    printf("%s\n", buffer);
 
    rewind(fp);               /* flush buffer and rewind file */
    char buf[20];
    fgets(buf,sizeof buf,fp);
    printf("%s\n", buf);
 
    fclose(fp);
 
    return 0;
}

Output:

aaa
aaabbb
aaabbbccc
file_size = 9
aaabbbccc
dddbbbccc
dddeeeccc
aaabbbcccdddeee

See also

setvbuf	sets the buffer and its size for a file stream (function)
C++ documentation for setbuf