[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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LEARN ABOUT ULTRIX

trpt

trpt(8c) trpt(8c)

Name
trpt - transliterate protocol trace

Syntax
trpt [ -a ] [ -s ] [ -t ] [ -j ] [ -p hex-address ] [ system [ core ] ]

Description
The command interrogates the buffer of TCP trace records created when a socket is marked for debugging and prints a readable description of
these records.

Options
When no options are supplied, prints all the trace records found in the system grouped according to TCP connection protocol control block
(PCB). The following options may be used to alter this behavior:

-s In addition to the normal output, prints a detailed description of the packet sequencing information.

-t In addition to the normal output, prints the values for all timers at each point in the trace.

-j Gives a list of the protocol control block addresses for which there are trace records.

-p Shows only trace records associated with the protocol control block whose address follows.

-a In addition to the normal output, prints the values of the source and destination addresses for each packet recorded.

The recommended use of is to isolate the problem and enable debugging on the socket(s) involved in the connection. Find the address of the
protocol control blocks associated with the sockets using the -A option to Then run with the -p option, supplying the associated protocol
control block addresses. If there are many sockets using the debugging option, the -j option may be useful in checking to see if any trace
records are present for the socket in question.

If debugging is being performed on a system or core file other than the default, the last two arguments may be used to supplant the
defaults.

Diagnostics
no namelist
The system image does not contain the proper symbols to find the trace buffer.

Other diagnostic messages are self-explanatory.

Files
See Also
netstat(1), setsockopt(2)

trpt(8c)