std::setbuf
| Defined in header <cstdio>
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void setbuf( std::FILE* stream, char* buffer );
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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, nullptr, _IONBF, 0), which turns off buffering.
Contents
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, the range [buffer, buffer + BUFSIZ) must be valid
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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
Example
std::setbuf may be used to disable buffering on streams that require immediate output.
#include <chrono>
#include <cstdio>
#include <thread>
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:
ab
See also
| sets the buffer and its size for a file stream (function) | |
C documentation for setbuf
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