Question about the System() function...

YankeePride13 · 11-17-2005, 04:55 PM

I am writing a program that acts like a shell. I used the System() function to compute the commands, however, I realized that exit and cd do not work. I figured out how to make my own exit, however, I cannot figure out how to get cd to work...if anyone could help that'd be great, I appreciate it in advance....here's my code...

Code:

#include <iostream>
#include <stdlib.h>
#include <string>


void main()
{
        char cmd[100] = " ";

        cout << "Please enter command: ";
        cin.getline(cmd, 100);

        while (strcmp (cmd, "exit") !=0)
                {

                        system (cmd);
                        cout << "Please enter command: ";
                        cin.getline(cmd,100);
                }
                exit(1);
}

YankeePride13 · 11-17-2005, 06:08 PM

this is the updated code...

Code:

#include <iostream>
#include <stdlib.h>
#include <string>
#include <unistd.h>

void main()
{
        char cmd[100] = " ";
        char * pch;

        cout << "Please enter command: ";
        cin.getline(cmd, 100);

        while (strcmp (cmd, "exit") !=0)
        {
                if((cmd[0] == "c") && (cmd[1] == "d"))
                {
                        pch = strtok(cmd," ");
                        pch = strtok(NULL," ");
                        chdir(pch);
                }
                else
                {
                        system (cmd);
                        cout << "Please enter command: ";
                        cin.getline(cmd,100);
                }
        }
        exit(1);
}

and there are the errors im recieving from my linux compiler

test.cpp:16: ISO C++ forbids comparison between pointer and integer
test.cpp:16: ISO C++ forbids comparison between pointer and integer

any ideas?

-=SoKrA=- · 11-18-2005, 12:45 PM

You're getting those errors because you're comparing a string (char pointer) and an int.

You should change the line that says

Code:

if((cmd[0] == "c") && (cmd[1] == "d")

to

Code:

if((cmd[0] == 'd') && (cmd[1] == 'd')

and there you go. No more warning, and a working piece of code.

Also, please change the return value of main to int. Void is just wrong (see the FAQ or search the forums for the reason(s)).

It might be better to fork() and then exec(), but that's a bit more complicated.

Xipher · 11-18-2005, 02:41 PM

Im wondering why you wouldn't be getting errors with this, since cin and cout are in the std namespace, and I don't see a "using namespace std;" or any thing like that in your code. Also, its int main, not void.

-=SoKrA=- · 11-18-2005, 02:45 PM

He's probably using some very permissive compiler. My g++ erros out on void main().

Also, I suspect this is not the code verbatim, because the line where he's got the error and it's actual line in the code he posted are different.

11-17-2005, 04:55 PM	#1
YankeePride13 Registered User Join Date: Nov 2005 Posts: 36	Question about the System() function... I am writing a program that acts like a shell. I used the System() function to compute the commands, however, I realized that exit and cd do not work. I figured out how to make my own exit, however, I cannot figure out how to get cd to work...if anyone could help that'd be great, I appreciate it in advance....here's my code... Code: #include <iostream> #include <stdlib.h> #include <string> void main() { char cmd[100] = " "; cout << "Please enter command: "; cin.getline(cmd, 100); while (strcmp (cmd, "exit") !=0) { system (cmd); cout << "Please enter command: "; cin.getline(cmd,100); } exit(1); }
YankeePride13 is offline

11-18-2005, 12:45 PM	#3
-=SoKrA=- Me Join Date: Oct 2002 Location: Europe Posts: 448	You're getting those errors because you're comparing a string (char pointer) and an int. You should change the line that says Code: if((cmd[0] == "c") && (cmd[1] == "d") to Code: if((cmd[0] == 'd') && (cmd[1] == 'd') and there you go. No more warning, and a working piece of code. Also, please change the return value of main to int. Void is just wrong (see the FAQ or search the forums for the reason(s)). It might be better to fork() and then exec(), but that's a bit more complicated. __________________ SoKrA-BTS "Judge not the program I made, but the one I've yet to code" I say what I say, I mean what I mean. IDE: emacs + make + gcc and proud of it.
-=SoKrA=- is offline

11-18-2005, 02:41 PM	#4
Xipher Registered User Join Date: Sep 2004 Posts: 197	Im wondering why you wouldn't be getting errors with this, since cin and cout are in the std namespace, and I don't see a "using namespace std;" or any thing like that in your code. Also, its int main, not void. __________________ If any part of my post is incorrect, please correct me. This post is not guarantied to be correct, and is not to be taken as a matter of fact, but of opinion or a guess, unless otherwise noted.
Xipher is offline

11-18-2005, 02:45 PM	#5
-=SoKrA=- Me Join Date: Oct 2002 Location: Europe Posts: 448	He's probably using some very permissive compiler. My g++ erros out on void main(). Also, I suspect this is not the code verbatim, because the line where he's got the error and it's actual line in the code he posted are different. __________________ SoKrA-BTS "Judge not the program I made, but the one I've yet to code" I say what I say, I mean what I mean. IDE: emacs + make + gcc and proud of it.
-=SoKrA=- is offline

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
question abt function system();	errtime	C Programming	2	10-01-2007 01:24 PM
Screwy Linker Error - VC2005	Tonto	C++ Programming	5	06-19-2007 02:39 PM
measuring system resources used by a function	Aran	C Programming	1	03-13-2006 05:35 PM
Including lib in a lib	bibiteinfo	C++ Programming	0	02-07-2006 02:28 PM
[question]Simulating the Reliability of a Component-Based System	burbose	C Programming	3	06-13-2005 07:28 AM