use fprintf to write to the console

[baumann@pan]

hi all,

i want to use the fprintf to make log.

if defined LOG_TO_FILE, it is easy to use fprintf to write the log
file.

if not defined LOG_TO_FILE, i want to simply write to error std
console.


how can I do so with fprintf since fprintf only accept FILE*? while
error std console has int value 2.

[Richard Bos]

Re: use fprintf to write to the console

"baumann@pa n" <baumann.Pan@gm ail.com> wrote:
[color=blue]
> if defined LOG_TO_FILE, it is easy to use fprintf to write the log
> file.
>
> if not defined LOG_TO_FILE, i want to simply write to error std
> console.[/color]

You mean, to stderr?
[color=blue]
> how can I do so with fprintf since fprintf only accept FILE*? while
> error std console has int value 2.[/color]

There is no "error std console" with any int value, even 2, in ISO C.
You may be thinking of POSIX.

stderr is a FILE *.

Richard

[pete]

Re: use fprintf to write to the console

baumann@pan wrote:[color=blue]
>
> hi all,
>
> i want to use the fprintf to make log.
>
> if defined LOG_TO_FILE, it is easy to use fprintf to write the log
> file.
>
> if not defined LOG_TO_FILE, i want to simply write to error std
> console.
>
> how can I do so with fprintf since fprintf only accept FILE*? while
> error std console has int value 2.[/color]

#include <stdio.h>

int main(void)
{
fprintf(stderr, "%s",
"if not defined LOG_TO_FILE, "
"i want to simply write to error std console.\n"
"how can I do so with fprintf since fprintf only "
"accept FILE*?\n"
"whileerror std console has int value 2.\n"
);
return 0;
}

--
pete

[CBFalconer]

Re: use fprintf to write to the console

"baumann@pa n" wrote:[color=blue]
>
> i want to use the fprintf to make log.
>
> if defined LOG_TO_FILE, it is easy to use fprintf to write the log
> file.
>
> if not defined LOG_TO_FILE, i want to simply write to error std
> console.
>
> how can I do so with fprintf since fprintf only accept FILE*? while
> error std console has int value 2.[/color]

#define LOG_TO_FILE 1 /* or 0, or leave undefined */
.....
FILE *reporterrs;
.....
if (LOG_TO_FILE) {
reporterrs = fopen(......);
}
else reporterrs = stderr;
.....
/* use reporterrs */
if (LOG_TO_FILE) fclose(reporter rs);

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[Walter Roberson]

Re: use fprintf to write to the console

In article <428A17C9.6E774 0E2@yahoo.com>,
CBFalconer <cbfalconer@wor ldnet.att.net> wrote:[color=blue]
>#define LOG_TO_FILE 1 /* or 0, or leave undefined */[/color]
[color=blue]
> if (LOG_TO_FILE) {[/color]

Small slip there: if you leave LOG_TO_FILE undefined, then in the
if statement, it is going to be treated as an undefined variable
with compiler-dependant results.

I suspect it momentarily slipped your mind that treating
an undefined macro as the value 0 only occurs while evaluating
preprocessing conditional expressions.
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