How does one properly use the Unix exec C(++)-command?

Question

Specifically, I need to call a version of exec that maintains the current working directory and sends standard out to the same terminal as the program calling exec. I also have a vector of string arguments I need to pass somehow, and I'm wondering how I would go about doing all of this. I've been told that all of this is possible exclusively with fork and exec , and given the terrible lack of documentation on the google, I've been unable to get the exec part working.

What exec method am I looking for that can accomplish this, and how do I call it?

Answer 1

If you have a vector of strings then you need to convert it to an array of char* and call execvp

#include <cstdio>
#include <string>
#include <vector>

#include <sys/wait.h>
#include <unistd.h>

int main() {
    using namespace std;

    vector<string> args;
    args.push_back("Hello");
    args.push_back("World");

    char **argv = new char*[args.size() + 2];
    argv[0] = "echo";
    argv[args.size() + 1] = NULL;
    for(unsigned int c=0; c<args.size(); c++)
        argv[c+1] = (char*)args[c].c_str();

    switch (fork()) {
    case -1:
        perror("fork");
        return 1;

    case 0:
        execvp(argv[0], argv);
        // execvp only returns on error
        perror("execvp");
        return 1;

    default:
        wait(0);
    }
    return 0;
}

Answer 2

您可能正在寻找execv（）或execvp（） 。

Answer 3

You don't necessarily need google to find this out, you should have the man command available so you can man fork and man exec (or maybe man 2 fork and man 3 exec ) to find out about how the parameters to these system and library functions should be formed.

In Debian and Ubuntu, these man pages are in the manpages-dev package which can be installed using synaptic or with:

sudo apt-get install manpages-dev