Help needed with system() and popen!

twirl · 09-13-2005, 02:12 PM

Hi,

my book dont cover system or popen enough for what i need to do, my book only mentions system but dont say how to use it and dont even mention popen.

I would like to be able to use either system() or popen to enter the path of a user specifys what is stored in games.db and then execute the command next to path what is stored in games.db at the moment i have my games.db file as :-

path;./startfile:Gamename aka /home/twirl/bf1942;./start.sh:Battlefield 1942

and i would like system to enter the path what is specified in games.db and then execute ./start.sh for example and continue doing that throughout the games.db file.

My code is below :-

Code:

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
 
int main()
{
 int i=0;
 char s1[80],s2[40],s3[90],s4[256],s5[90];      // set char size for input
 ofstream outfile("games.db", ios::app);
 string whole,p1,p2;
 ifstream infile;
 
// Start Main Menu
 
 char choice='\0';//NULL;
 bool finished=false;
 while (finished != true) 
 {
  cout<<"MAIN MENU\n";
  cout<<"1. AddGame\n";
  cout<<"2. Options\n";
  cout<<"3. RunGame\n";
  cout<<"4. Exit\n";
  cout << "Please enter your choice: ";
  cin>>choice;
  cout<<"\n\n";
 
  // Start function for submenu
  switch(choice) 
  {
   case '1': cout << "1. Add Game To DB\n";
             cout << "2. Go back\n";
             cout << "Please enter your choice: ";
             cin>>choice;
 
             if(choice == '1')
             {
              cout << "\n\nPlease enter full-path to game: ";
                          cin.get();
                          cin.getline (s1, 80); // Input goes in
                          outfile << s1 << ";"; // add ; after each path
               
              cout << "\n\nPlease enter name of startup file: e.g ./start.sh ";
                          cin.get();
                          cin.getline (s2, 40); // Input goes in$
                          outfile << s2 << ":";  // add : after each startup file
			   cout << "\n\nPlease enter game name: ";
                          cin.getline (s3, 90); 
                          outfile << s3 << "\n";
                if (outfile.is_open())
                          {
                           outfile.close();
                          }
                         }
             /* Just break if choice != 1 */
             break;
   case '2': cout<<"Options\n";
             cout<<"1. Edit Game Config\n";
             cout<<"2. Go back\n";
             cout << "Please enter your choice: ";
             cin>>choice;
             
             if(choice=='1')
             {
              cout << "Please enter full path to config file to edit: ";  // ask user for path to config file
              cin.get();
              cin.getline (s4, 256);        // input goes in
              string cmd = string("pico ") + string(s2);
              system(cmd.data());      // open up pico to edit config
             } 
    case '3': cout<<"Run Game";
             i=0;
             infile.open ("games.db", ios::in);  
             while(getline(infile,whole)){
                 i++;
                 p2=whole.substr(whole.find(':')+1,whole.length());  
                 cout << i << ". " << p2 << endl;
             }                  
             cout << "Please select game you wish to run: " << endl;
             cin.get();
             cin.getline(s5, 100);
             i=1;
             infile.open ("games.db", ios::in);  
             while(getline(infile,whole)){
                 i++;
                 if(atoi(s5)!=i)
                     continue;
                 p1=whole.substr(0,whole.find(':'));  
             }              
             system ( string(p1+" > system_errors").c_str() );
                         
                         // Here we would check 'choice' and probably move to another functi$
             cout<<"\n\n";
             break;
   
             // Here we would check 'choice' and probably move to another functi$
             cout<<"\n\n";
             break;

   case '4': //Finished so set finished 'true' to break out of loop
             finished=true;
             cout<<"Exiting....\n";
             break;
   default:  //If choice !=1/2/3 then do what it says here
             break;
 
     outfile.close();           // close file games.db
 
             //  end functions
  }
  choice='\0'; //NULL
 }
 return 1;
}

schneidz · 09-13-2005, 02:54 PM

Quote:

I would like to be able to use either system() or popen to enter the path of a user specifys what is stored in games.db and then execute the command next to path what is stored in games.db at the moment i have my games.db file as :-

path;./startfile:Gamename aka /home/twirl/bf1942;./start.sh:Battlefield 1942

and i would like system to enter the path what is specified in games.db and then execute ./start.sh for example and continue doing that throughout the games.db file.

you would need to call system in a loop for each line in games.db

Code:

man system
system("cd /home/twirl/bf1942; ./start.sh");

also, look at 'man sprintf' to cat your command line to system. e.g:

Code:

   sprintf(buff, "bunzip2 %s", argv[1]);
   system(buff);

twirl · 09-13-2005, 03:15 PM

hi,

hmm i think i can cd into the dir by doing system(s1); and then do exec(s2); and if i put them into a loop would that work?

thankyou

twirl · 09-13-2005, 03:17 PM

OOps

I meant system(cd s1); exec(s2);

can i do something like that?

schneidz · 09-14-2005, 09:22 AM

when you call 'exec' in a loop not only will it break out of the loop, it will break out of the program. exec replaces the new programs memory with the current memory address and you cant get it back.

usually you would fork and if not parent exec.

Quote:

from hko:
This "fork() a child proces, exec() another program, and wait for it to finish" is needed quite often. Therefore there is a library function that does all of this at once: system()

basically what i was alluding to in my previous post is that you need to parse the string argument passed to 'system' somehow. (system is the equivelent of manually typing in something in the shell).

p.s. - don't use 'cd', just execute the /fully/qualified/path/name