00forker.cpp

#include <sstream>
#include <iostream>
#include <iomanip>
#include <string>
#include <set>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <climits>
#include <ctime>
#include <unistd.h>
using namespace std;

int main(int argc, char **argv){
	cin.tie(0);
	ios::sync_with_stdio(false);
	if(argc<3){
		cerr<<"forker program(chmod+x) validator args..."<<endl;
		return 0;
	}
	const char *cmd=argv[2];

	//Initialize
	int fd_in[2],fd_out[2];
	pipe(fd_in);
	pipe(fd_out);

	int pid1=fork();
	if(pid1==-1){
		cout<<"InternalError"<<endl;
		return 0;
	}
	if(pid1==0){//validator
		close(1);
		dup2(fd_in[1],1);
		close(0);
		dup2(fd_out[0],0);
		close(fd_in[0]);
		close(fd_in[1]);
		close(fd_out[0]);
		close(fd_out[1]);
		char **args=(char**)malloc(sizeof(char*)*argc);
		for(int i=2;i<argc;i++)args[i-2]=argv[i];
		args[argc-2]=NULL;
		execvp(cmd,args); //execvp is required; cmd might be interpreter name
		free(args);
		return 0;
	}
	int pid2=fork();
	if(pid2==-1){
		cout<<"InternalError"<<endl;
		return 0;
	}
	if(pid2==0){//program
		close(0);
		dup2(fd_in[0],0);
		close(1);
		dup2(fd_out[1],1);
		close(fd_in[0]);
		close(fd_in[1]);
		close(fd_out[0]);
		close(fd_out[1]);
		char **args=(char**)malloc(sizeof(char*)*2);
		args[0]=argv[1];
		args[1]=NULL;
		execvp(argv[1],args); //argv[1] must be chmod +x
		free(args);
		return 0;
	}
	close(fd_in[0]);
	close(fd_in[1]);
	close(fd_out[0]);
	close(fd_out[1]);
	
	int st1,st2;
	waitpid(pid1,&st1,WUNTRACED);
	waitpid(pid2,&st2,WUNTRACED);
	//status=0 == AC
	if(WIFEXITED(st1))cout<<"status="<<WEXITSTATUS(st1)<<endl;
	else cout<<"status=255"<<endl;
}