Integrating Unix and C++

[DigitalPython]

I use Red Hat Linux and I use the gcc/c++ compiler that came with it. When I want to write a program that uses the system, I use the syscall.h header file.<br><br>For example, to see how many lines in a file:<br>&nbsp;&nbsp;&nbsp;&nbsp;<font color=red><FONT FACE=monospace>system(&quot;wc -l /etc/passwd&quot;</font></font><br><br>The output to the screen would be a number. <b>How would I set that number to a integer value in C++?</b><br>I have tried things like:<br>&nbsp;&nbsp;&nbsp;&nbsp;<font color=red><FONT FACE=monospace>int a;</font></font><br>&nbsp;&nbsp;&nbsp;&nbsp;<font color=red><FONT FACE=monospace>a=system(&quot;wc -l /etc/passwd&quot; </font></font><br><br>but that doesn't help at all. I know that that calls a system command, but there should be a way to set a system to response to a variable. Please tell me how to do this or supply a little code that shows how its done. THANKS.<br>

 

[MikeLacey]

Hi DigitalPython,

The function [tt]popen[/tt] will do what you want.

It lets you run an external command and read that commands output as if it were a file.
Mike
michael.j.lacey@ntlworld.com

 

[jad]

a=system(...)

would make a = to the exit status of the system call ...

if it was ok, it would return 1 for instance ...

popen, is short for 'pipe open' allowing you to get the output from a command into C++ ...
(not Stealing MikeLaceys thunder really just explaining)

 

[MikeLacey]

<grin> no worries Jad
Mike
michael.j.lacey@ntlworld.com

 

[dejoe]

So what would the popen syntax look like?

dejoe

 

[MikeLacey]

From the solaris man page for popen

The following program will print on the standard output (see stdio(3S)) the names of files in the current directory with a .c suffix.
[tt]
main(){
[tab]char *cmd = &quot;/usr/bin/ls *.c&quot;;
[tab]char buf[BUFSIZ];
[tab]FILE *ptr;
[tab]if ((ptr = popen(cmd, &quot;r&quot) != NULL)
[tab][tab]while (fgets(buf, BUFSIZ, ptr) != NULL)
[tab][tab][tab](void) printf(&quot;%s&quot;, buf);
[tab]return 0;
}
[/tt] Mike
michael.j.lacey@ntlworld.com
Email welcome if you're in a hurry or something -- but post in tek-tips as well please, and I will post my reply here as well.