How to get a full path of a process with C language

A process's command line is saved in file/proc/pid/cmdline, and the parameters are delimited by byte 0. The following applet shows an example of how to read this file.

#include <iostream>
#include <fstream>

int main(int argc, char* argv[]) {
　 if(argc != 2) {
　　　 printf("usage: %s pid ", argv[0]);
　　　 exit(0);
　 }

　 std::string path(argv[1]);
　 path = "/proc/" + path + "/cmdline";
　 std::ifstream fin(path.c_str());
　 if(!fin) {
　　　 std::cout << "Open /proc/" << argv[1] << "/cmdline failed! ";
　　　 exit(-1);
　 }
　 std::string s;
　 while (getline(fin, s, ''))
　 {
　　　 std::cout << s << std::endl;
　 }
}