Name

fflush - flush a stream’s buffer

Synopsis

#include <stdio.h>

int fflush(FILE *stream);

Description

For output streams, fflush() forces a write of all user-space buffered data for the given output or update stream via the stream’s underlying write function.

If stream is NULL, fflush() flushes all open output streams.

Example

#include <stdio.h>

int main() {
    // This line will be buffered because it doesn't end in a newline
    printf("This text is not followed by a newline");

    // Wait several seconds (compile with -O0 to prevent this being optimized out)
    for (size_t i = 0; i < 1000000000; i++) {}

    // Flush stdout's buffer. This will print the line to the terminal.
    fflush(stdout);

    // Wait again
    for (size_t i = 0; i < 1000000000; i++) {}
}

Return Value

Upon successful completion 0 is returned. Otherwise, EOF is returned and errno is set to indicate the error.

Errors

EBADF: stream is not an open stream, or is not open for writing.

fflush() may also fail and set errno for any of the errors specified for write().