| Defined in header <cstdio> | ||||
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Sets the internal buffer to use for I/O operations performed on the C stream stream.
If buffer is not null, equivalent to std::setvbuf(stream, buffer, _IOFBF, BUFSIZ).
If buffer is null, equivalent to std::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. If not null, must be able to hold at least BUFSIZ characters |
Return value
(none).
Notes
If BUFSIZ is not the appropriate buffer size, std::setvbuf can be used to change it.
std::setvbuf should also be used to detect errors, since std::setbuf does not indicate success or failure.
This function may only be used after stream has been associated with an open file, but before any other operation (other than a failed call to std::setbuf/std::setvbuf).
A common error is setting the buffer of stdin or stdout to an array whose lifetime ends before the program terminates:
1 2 3 4 | int main() { char buf[BUFSIZ]; std::setbuf(stdin, buf);} // lifetime of buf ends, undefined behavior |
Example
setbuf may be used to disable buffering on streams that require immediate output.
1 2 3 4 5 6 7 8 9 10 11 12 13 | #include <cstdio>#include <thread>#include <chrono> int main(){ using namespace std::literals; std::setbuf(stdout, NULL); // unbuffered stdout std::putchar('a'); // appears immediately on unbuffered stream std::this_thread::sleep_for(1s); std::putchar('b');} |
Output:
1 |
See also
| sets the buffer and its size for a file stream (function) | |
C documentation for setbuf | |
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