CODEWITHSUNDEEP
cunixprocess
hari
hari

Reputation: 9733

program not executing anything after a call to system()

I am calling a command via system(command) call. But no other code is executed after this system() call.

Why is so? I thought, system() would create a child process for "command" execution and my program (parent of "command"-child) will continue executing code after that.

Am I not understanding system() correctly?

code:

printf("before \n");
system("tail -f filename");       /* long lived - never returns */
printf("after \n");

Here, I do not see after getting printed ever.

Upvotes: 3

Views: 3971

Answers (3)

slashmais
slashmais

Reputation: 7155

A bit late but here is a solution (tested and working on Linux):

#include <sstream>
#include <cstdlib> //for system()-calls
#include <thread>


//just a utility-function..
template<typename...P> std::string says(P...p)
    {
        std::string r{};
        std::stringstream ss("");
        (ss<<...<<p);
        r=ss.str();
        return r;
    }

#if defined(YOUR_COMPILERS_LINUX_DETECTION_FLAG)
template<typename...T> void _S_R_A_(const std::string &sc)
    {
        std::string s{};
        s=says("nohup ", sc, " 1&2>/dev/null &"); //like old Windows TSR-call
        std::system(s.c_str());
    }
#else // if defined(YOUR_COMPILERS_WINDOWS_DETECTION_FLAG)
template<typename...T> void _S_R_A_(const std::string &sc) //assuming windows - NOT TESTED!
    {
        std::string s{};
        s=says("start ", sc);
        std::system(s.c_str());
    }
#endif

template<typename...T> void SysRunApp(const std::string &sApp, T...t)
    {
        std::string sa{};
        sa=says(sa, sApp, " ", t...); //caller must ensure parameters are
                                      //correctly spaced/escaped etc
        std::thread(_S_R_A_, sa).detach();
    }

Upvotes: 0

Nikolai Fetissov
Nikolai Fetissov

Reputation: 84169

The system(3) function causes your process to wait for the completion of the child.

Edit 0:

You have to use the classic pair of fork(2) and execve(2) for what you want to do. You might also check whether your C library provides POSIX spawn(3).

Edit 1:

Look into waitpid(2) to keep the parent around.

Upvotes: 8

Intrepidd
Intrepidd

Reputation: 20878

You have to fork(2) to continue executing code.

Upvotes: 0

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