Difference between revisions of "cpp/io/c/setbuf"
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If {{lc|BUFSIZ}} is not the appropriate buffer size, {{lc|std::setvbuf}} can be used to change it. | If {{lc|BUFSIZ}} is not the appropriate buffer size, {{lc|std::setvbuf}} can be used to change it. | ||
| − | {{lc|std::setvbuf}} should also be used to detect errors, since {{ | + | {{lc|std::setvbuf}} should also be used to detect errors, since {{tt|std::setbuf}} does not indicate success or failure. |
| − | This function may only be used after {{c|stream}} has been associated with an open file, but before any other operation (other than a failed call to {{ | + | This function may only be used after {{c|stream}} has been associated with an open file, but before any other operation (other than a failed call to {{tt|std::setbuf}}/{{lc|std::setvbuf}}). |
| − | A common error is setting the buffer of {{ | + | A common error is setting the buffer of {{lc|stdin}} or {{lc|stdout}} to an array whose lifetime ends before the program terminates: |
{{source|1= | {{source|1= | ||
int main() | int main() | ||
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===Example=== | ===Example=== | ||
{{example | {{example | ||
| − | |{{ | + | |{{tt|std::setbuf}} may be used to disable buffering on streams that require immediate output. |
|code= | |code= | ||
#include <chrono> | #include <chrono> | ||
Latest revision as of 11:35, 13 September 2023
| 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 |
[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
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[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() { 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
[edit] See also
| sets the buffer and its size for a file stream (function) | |
| C documentation for setbuf
| |
