I've been checking out the code of a lot of my favorite programs written in C, and I just don't understand... Why do they sometimes output text using printf(, sometimes fprintf( to stdout and sometimes fprintf( to stderr??? What's the difference?
Thanks.
It's a matter of pure control over which stream is actually used for some.
When one needs to output an error message, fprintf on stderr is logical to use.
Thanks a lot.
So it is really not much of a difference then. Although, I'm not so sure, but it seems that the program I got this from uses fprintf to stdin so that GUIs can parse the output easier. Again, I'm not sure if it's exactly the reason (I just saw some GUI parsing talk on comments) and I don't know why this is significant for GUIs.
Edit: P.S.: and it uses fprintf to stderr for the help text.
printf is the same thing as fprintf(stdout, it's just a matter of style.
stdout goes to standard output, stderr standard error.
both stdout and stderr are both redirected to the console (the screen) by default. But you can change that, by redirecting one or both to one or two files, or piping them to different application's input, or whatever. So there is some difference.
search for file redirection.
Well it is good practice to end a printf statement with a '\n'.
For me it is sounds like "it is good practice to use bus for getting to your destination"Quote:
Originally Posted by slingerland3g
I think the best trasportation type depends on the route... As well as adding \n in printf depends on the target...
What makes stderr useful is that, were you, for example, to pipe output that's written to stdout to a file, you could write potential error messages to stderr, and they'd still be written to the console.
Take the following example:
Were this compiled, provided this piece of code was in a valid, compilable context, and executed with "program.exe > somefile.txt", you would get "Writing a number to a file." on the console while "Some number" would be written to somefile.txt.Code:
fprintf(stderr, "Writing number to file.\n");
printf("Some number");
I think what's more important is that if you're using \n in printf (and why wouldn't you? Most of the time you want output to be on separate lines), you put the \n at the end. I worked with a guy once who insisted on writing his debug as:Quote:
Originally Posted by vart
In this case if foo crashes you won't see the output of the first printf, unless something else flushes the buffer first.Code:printf ("\nCalling foo");
foo();
printf ("\nReturned from foo");
QuantumPete