std::setbuf
Defined in header <cstdio> | ||
void setbuf(std::FILE* stream, char* buffer ); | ||
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.
Contents |
[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 <chrono>#include <cstdio>#include <thread> int main(){usingnamespace std::chrono_literals; std::setbuf(stdout, nullptr);// unbuffered stdoutstd::putchar('a');// appears immediately on unbuffered streamstd::this_thread::sleep_for(1s);std::putchar('b');}
Output:
ab
[edit]See also
| sets the buffer and its size for a file stream (function) | |
C documentation for setbuf | |
