[C language] system function print output when not expected. Post: 302418447

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Top Forums Programming [C language] system function print output when not expected. Post 302418447 by ejdv on Tuesday 4th of May 2010 10:03:29 AM

05-04-2010

Registered User

[C language] system function print output when not expected.

Hi,

I am new to C and have a little problem.
I am not planning to be a C expert, but this would be nice to understand.

The problem is that a 'system' call prints it output to stdout, when I do not expect this.

This is the program:

trial.c

Code:

#include <ctype.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>


int main() {

fprintf(stdout, "-> main()\n");

int return_value;
char passing_var[9];

strcpy(passing_var, "datum");

fprintf(stdout, "main() passing_var  = %s\n",passing_var);

return_value=date(passing_var);

fprintf(stdout, "main() return_value = %s\n",return_value);
fprintf(stdout, "<- main()\n");

}


int date(char *passing_var) {

fprintf(stdout, "-> date()\n");
fprintf(stdout, "date() passing_var  = %s\n",passing_var);

char command[128];
int date_return;

strcpy(command, "date");

fprintf(stdout, "date() command      = %s\n",command);

date_return=system(command);

fprintf(stdout, "date() date_return  = %s\n",date_return);
fprintf(stdout, "<- date()\n");

return date_return;

}

This is the output:

# ./trial

Code:

-> main()
main() passing_var  = datum
-> date()
date() passing_var  = datum
date() command      = date
Tue May  4 13:53:42 GMT 2010
date() date_return  =
<- date()
main() return_value =
<- main()

I do not understand why the 'date' output is printed in the 'date()' subroutine and not given to the 'date_value' variable.

Probably wrong declarations and other mistakes.

Can someone help and shine a light on this ?

Many thanks in advance,

E.J.

ejdv

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cr_perror

cr_perror(3)						     Library Functions Manual						      cr_perror(3)

NAME

       cr_perror - print a libcrash error or warning message

SYNOPSIS

DESCRIPTION

       prints  to standard error an error or warning message corresponding to error, which should be the return value from an immediately previous
       call to one of the libcrash calls.  The message describes the problem that occurred, explains its implications when appropriate, and  gives
       corrective action where appropriate.

       If  called with a zero error value, indicating success, prints nothing.	Therefore, it can be called after each libcrash call without harm.
       (If called after with the flag set, repeated error messages may result.)

       crash_cb should be the same crash dump descriptor as was passed to the call that returned error.  If the  call  was  pass  the  crash  dump
       descriptor returned by that call, even if it is NULL.

       If  error  is indicating that the system variable contains the error information, will refer to to print the appropriate message.  In these
       cases it is critical that be called immediately after the offending libcrash call returns.

AUTHOR

       was developed by HP.

SEE ALSO

       cr_open(3), cr_verify(3), libcrash(5).

																      cr_perror(3)