Thread: Program to check for running pid using system call in UNIX/linux

I have written a program which uses a pid to check if the process is currently running and return a value based on the system call result.

But the program core dumps

Code:

#include <stdio.h>
#include <string.h>
 
int main( argc, argv )
int argc;
char * argv[];
{
     int p_pid = 99;
     char buff[1000];
      
 
    const char *program_name = basename(argv[0]);
 
    memset( buff, '\0', sizeof( buff));
    sprintf(buff, " ps -ef | grep %s | grep %d ", program_name,  p_pid);
 
    printf("this is %s", buff);
 
    if( system(buff) == 0 )
     {
       printf(" system call returns 0 ");
     }
    else
     {
        printf("system call is non zero");
     }
 
}

What is the mistake in this code and is it portable in both unix/linux , is the method secure (grepping for program name )?

> int main( argc, argv )
> int argc;
> char * argv[];
This style was officially obsolete in 1989.
What ancient dusty text are you learning from?

> int p_pid = 99;
What's this got to do with anything.

As for your core dump, maybe you need to compile with warnings turned on. basename is defined in a different header, so maybe you're ending up with a wrong prototype for this function, I couldn't produce this error on my system.

As for your problem (finding the pid), then Hodor is right you should use getpid() rather than passing commandlines to system. The following works for me

Code:

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

int main(int argc, char *argv[])
{
    const char *program_name = basename(argv[0]);
    if (argc != 1) {
        printf("Usage: %s\n", program_name);
        exit(1);
    }
    
    pid_t program_pid = getpid();
    printf("%s has pid %d\n", program_name, (int)program_pid);
    
    return 0;
}

Originally Posted by selvankj

I don't have to get the pid, I have it already, just wanted to check if the pid I have matches with the pid of the current running process,....thanks for letting me know of using an obselete style of program which am using, but you have just not answered by question...

If you have the pid, let's call it MYPID. And you have the real pid, let's call it REALPID, then how does this not allow you to check if the pid you have matches the pid of the current running process. I think you might be overthinking the problem.

Code:

/* Pseudocode 

if MYPID = REALPID, then:
   "Yes"
else:
   "No"

*/