Need to get the PID of a process

[iccollado]

How do I run a process from a C++ program and obtain its PID? Right now I am doing in a "parallel" thread:

system("ampl method.run");

and into the main function (after running the thread mentioned before):

sleep(5); //Just to be sure that the thread is executing the ampl command
system("ps -Ac| grep ampl | awk '{print $1}' > ~/AMPL_PID.txt");

This doesn't work. The main program hangs in the "system" function while the thread continues to execute. Once I manually kill the ampl process in the thread, the main program continues and writes the system("ps -Ac...") output to the desired location.

I need to be able to obtain the ampl command PID in order to later kill it (if necessary). Any ideas how to make this work or how to do this?

[jsmith]

Use fork() and exec().

fork() creates a child process. The parent receives the PID of the child.
The child should then exec() whatever it is you want to run.

[Duthomhas]

With system(), you can't (not easily, anyway).
http://linux.die.net/man/3/posix_spawnp
http://linux.die.net/man/3/popen

Hope this helps.

[edit] yoink! too late. I should mention that using fork() and exec() together are more likely to be available than spawn()...

[anishsane]

Use pgrep

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

#ifdef WIN32
FILE *popen ( const char* command, const char* flags) {return _popen(command,flags);}
int pclose ( FILE* fd) { return _pclose(fd);}
#endif

int main(int argc, char* argv[])
{
class="quote">
class="qd">
    char psBuffer[128];
    FILE *iopipe;

if( (iopipe = popen( "pgrep ampl", "r" )) == NULL )exit( 1 );
//ampl is the command (executable) whose pid you want to find
while( !feof( iopipe ) )
    {
        if( fgets( psBuffer, 128, iopipe ) != NULL )
            puts( psBuffer ); // or use atoi(psBuffer) to get numerical value
    }
    printf( "\nProcess returned %d\n", pclose( iopipe ) );
    return 0;
}

use quoted part in your other thread