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std::setbuf

From cppreference.com
< cpp‎ | io‎ | c
 
 
Input/output library
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(deprecated in C++98)
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(deprecated in C++98)
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(C++11)
 
 
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, NULL, _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

setbuf may be used to disable buffering on streams that require immediate output

#include <cstdio>
#include <thread>
#include <chrono>
 
int main()
{
    using namespace std::chrono_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:

ab

[edit] See also

sets the buffer and its size for a file stream
(function) [edit]
C documentation for setbuf