I want to turn off the buffering for the stdout for getting the exact result for the following code
while(1) {
printf(".");
sleep(1);
}
The code printf bunch of '.' only when buffer gets filled.
You can use the setvbuf function:
setvbuf(stdout, NULL, _IONBF, 0);
Here're some other links to the function.
POSIX
C/C++
You can also use setbuf
setbuf(stdout, NULL);
This will take care of everything
Use fflush(FILE *stream) with stdout as the parameter.
http://www.elook.org/programming/c/fflush.html
You can do this:
write(1, ".", 1);
instead of this:
printf(".");
Use fflush(stdout). You can use it after every printf call to force the buffer to flush.
Related
I want to turn off the buffering for the stdout for getting the exact result for the following code
while(1) {
printf(".");
sleep(1);
}
The code printf bunch of '.' only when buffer gets filled.
You can use the setvbuf function:
setvbuf(stdout, NULL, _IONBF, 0);
Here're some other links to the function.
POSIX
C/C++
You can also use setbuf
setbuf(stdout, NULL);
This will take care of everything
Use fflush(FILE *stream) with stdout as the parameter.
http://www.elook.org/programming/c/fflush.html
You can do this:
write(1, ".", 1);
instead of this:
printf(".");
Use fflush(stdout). You can use it after every printf call to force the buffer to flush.
I am using printf("%d", 15); and nothing prints on the console.
I tried calling setvbuf (stdout, NULL, _IONBF, 0); first, nothing changed.
Any ideas how to tackle this issue ?
printf buffers the output. It will not flush the buffer (i.e. actually write out the contents) until a newline is reached.
The best remedy is to use printf("%d\n", 15);. Alternatively you can flush the buffer using fflush(stdout);
You can suppress the buffering behaviour by writing setbuf(stdout, NULL); but I wouldn't recommend your interfering with the workings in that way.
When I run the code below, it runs the system command on the 4th last line before displaying the string 'proceeding' before it! I'm wondering why and how to fix it, any ideas?
if ((strlen(command)>0) && (command[strlen (command) - 1] == '\n'))
command[strlen (command) - 1] = '\0';
printf("proceeding"); // <-- the string
strcat(command,contents);
strcat(command,subject);
system(command); // <-- offending system command
sleep (1);
printf("\n ----- Search complete for: [%s]",command);
getchar();
There are of course variables such as 'command' and 'subject' which are manipulated and declared outside the code above, so If you need context than I will post the rest of the source code below.
Pull the chain and flush:
I.e.
After
printf("proceeding");
Put
fflush(stdout);
That will flush the stuff in the buffer (bowl!)
Before the system command is executed.
Try adding a '\n' to the printf.
It forces flushing the printf buffer. Otherwise, it is not necessary that printf immediately prints the passed params. You can google flushing the buffer latter
stdout is line buffered, so it will only display what's in the buffer after it reaches a newline
change printf("proceeding"); to printf("proceeding\n"); or flush stdout with fflush(stdout); will do the work.
The stdio stdout stream is line or fully buffered by default. To set it unbuffered (and to avoid having to write a fflush(stdout) after every output operation), use the ISO C setvbuf function declared in stdio.h:
setvbuf(stdout, (char *)NULL, _IONBF, 0);
once before doing the first I/O.
#include<stdio.h>
#include <unistd.h>
int main(){
while(1)
{
fprintf(stdout,"hello-out");
fprintf(stderr,"hello-err");
sleep(1);
}
return 0;
}
On compiling this programme in gcc and on executing it only prints hello-err and not hello-out.Why is that so?Can someone please explain the reason behind it?
If you add a '\n' to your message it will (or should), ie. "hello-out\n".
The reason being is that stdout is buffered in order to be more efficient, whereas stderr doesn't buffer it's output and is more appropriate for error messages and things that need to be printed immediately.
stdout will usually be flushed when:
A newline (\n) is to be printed
You read in from stdin
fflush() is called on it
EDIT: The other thing I wanted to add before my computer crashed...twice...was that you can also use setbuf(stdout, NULL); to disable buffering of stdout. I've done that before when I've had to use write() (Unix) and didn't want my output to be buffered.
It doesn't always print out the output to stdout because by design stdout is BUFFERED output, and stderr is unbuffered. In general, the for a buffered output stream, the stream is not dumped until the system is "free" to do so. So data can continue buffering for a long while, before it gets flushed. If you want to force the buffer to flush you can do so by hand using fflush
#include<stdio.h>
#include <unistd.h>
int main(){
while(1)
{
fprintf(stdout,"hello-out");
fflush(stdout); /* force flush */
fprintf(stderr,"hello-err");
sleep(1);
}
return 0;
}
Update: stdout is linebuffered when connected to a terminal, and simply buffered otherwise (e.g. a redirect or a pipe)
You forgot newlines (noted \n) in your strings. Or you need to call fflush(NULL); or at least fflush(stdout); before sleep(1);
And fprintf(stdout, ...) is the same as printf(...)
You need to output newlines or to call fflush because (at least on Linux) the stdout FILE buffer is line-buffered. This means that the C library is buffering data, and will really output it (using the write Linux system call) when the buffer is full enough, or when you flush it either with a new line, or by calling fflush. Buffering is needed because system calls are costly (calling write for every byte to be output is really too slow). Read also the man page of setbuf
The following code:
int z = 0;
while(z < 4)
{
printf("iteration %d\n",z);
sleep(1);
z++;
}
Works fine and stdout buffer is flushed every second if running the program from command line. However, when I try to access the program in a web browser (server - apache on linux, compiled executable (with gcc) handled through cgi), the content is displayed only after 4 seconds and not "step by step". I am looking for something like PHP's ob_flush(). And, by the way, is cgi the best way of processing compiled C executables?
Update: neither fflush(stdout) nor setvbuf(stdout, NULL, _IONBF, 0) is working!!! Works great after disabling mod_deflate.
I am not quite sure I understand your question correctly, but in C you can
Flush after each print (fflush)
Disable buffering (setbuf, setvbuf)
setvbuf(stdout, NULL, _IONBF, 0); /* this will disable buffering for stdout */
If these won't work, then either something else is doing buffering or buffering is not the problem.
You could try to fflush stdout after your printf.