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]

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.

You mean, to stderr?

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

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]

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.

#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;
}

 

[CBFalconer]

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.

#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(reporterrs);

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[Walter Roberson]

#define LOG_TO_FILE 1 /* or 0, or leave undefined */

if (LOG_TO_FILE) {

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.