std::setbuf - cppreference.com (original) (raw)
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, nullptr, _IONBF, 0), which turns off buffering.
[edit] Parameters
| stream | - | the file stream to set the buffer to |
|---|---|---|
| buffer | - | pointer to a buffer for the stream to use. If a null pointer is supplied, the buffering is turned off. If not null, must be able to hold at least BUFSIZ characters |
[edit] Return value
(none)
[edit] 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:
int main() { char buf[BUFSIZ]; std::setbuf(stdin, buf); } // lifetime of buf ends, undefined behavior
[edit] Example
std::setbuf may be used to disable buffering on streams that require immediate output.
#include #include #include int main() { using namespace std::chrono_literals; std::setbuf(stdout, nullptr); // unbuffered stdout std::putchar('a'); // appears immediately on unbuffered stream std::this_thread::sleep_for(1s); std::putchar('b'); }
Output: