fflush(stdout)

[ssharish2005]

Hi all,

Just a quick one. I had been forced to use fflush(stdout) on certain instances. Whats i wanted to know is, why doesn't the data doesn't get written unless i call the fflush(stdout) on certain cases. Is obvious symptoms for this cause?

Thanks in advance!

-ssharish

[laserlight]

Just a quick one. I had been forced to use fflush(stdout) on certain instances. Whats i wanted to know is, why doesn't the data doesn't get written unless i call the fflush(stdout) on certain cases. Is obvious symptoms for this cause?

The standard output stream is typically line buffered, so in the event that the buffer is not yet full or a newline is not yet encountered (or if there has not been intervening input), the output would remain in the buffer, hence fflush() is useful to flush the buffer.

[ssharish2005]

But what i thought was that printf itself internally would do that. I might wrong here.

-ssharish

[laserlight]

But what i thought was that printf itself internally would do that. I might wrong here.

Your own experience tells you that you are wrong
Of course, if the output stream is line buffered and you print a line then the buffer will be flushed.

[ssharish2005]

>Your own experience tells you that you are wrong
haha i might be. But wasn't sure.

-ssharish

[MK27]

>Your own experience tells you that you are wrong
haha i might be. But wasn't sure.

-ssharish

Yep. That's why if you are trying to track a segfault using printf(); always use "printf();fflush(stdout);" -- otherwise, you can be misled as to where the fault occurs because the output was left in the buffer (implying, wrongly, that execution had not yet reached the printf()).

[laserlight]

That's why if you are trying to track a segfault using printf(); always use "printf();fflush(stdout);"

It may be easier to just use fprintf() with the standard error stream, printing a new line at the end, since the standard error stream is guaranteed to not be fully buffered by default.