Quitting a program

[irsmart]

I have used this before, but I can't remember how to do it. In a console application, how do you quit using a system command? for example the

system("SOMETHING");

is the way I remember. Also, how do you use that same system function to clear the screen?

[twomers]

exit - system("exit"); I think is what you're looking for. Are you just trying to quit your program at a particular point? And system("cls"); clears screens, but there's a better way from the FAQ. If you're using Windows, the last is the best option. Just copy and paste the function.

[SlyMaelstrom]

Here is the deal... if you call a program with system, the calling program can't do anything until the program called is completed and the system call resolves. This includes attempting to close the program before it actually completes itself. This is one of the many reasons not to use system().

As for clearing the screen... there is no standard way. Check the FAQs... it has an entry on clearing the screen. It also talks about using system() in "Running a program from within a program".

[Wraithan]

Well to quit a program just return 0; in main().

Easier than doing some fancy stuff.

[Cat]

In fact returning from main() is by far the best way to exit a program; in C++ you should use nothing else. The reason is that in C++, unlike in C, you have objects with destructors that need to be called when the variables go out of scope.

For example, if your code writes to files, it would be rather nice to make sure the most up-to-date data was flushed to disk before your program ends, wouldn't it? ofstream's destructor will do that for you. If you bypass it with some C command, that doesn't happen.

Let the program die with dignity and grace, like it's supposed to.

[swgh]

Why don't you just do this?

exit(0);

It is simple and effective

[Cat]

Why don't you just do this?

exit(0);

It is simple and effective

It's also very bad, for exactly the reason I mentioned in the post before yours. exit() does not unwind the stack; it does not call destructors for objects. Any resource you allocated (which should be freed in some destructor somewhere) remains allocated. C++ file streams will not be flushed, resources you acquired from the OS will not be returned, cats and dogs will live together, etc.

Yes, it works in certain situations in certain kinds of code, but it's a very bad habit to get into.

This is included ONLY for backwards compatibility with C (it's a C function) -- and C didn't have destructors. In general it's one of those lines of code that simply shouldn't be used in C++.

If you want an equivalent in C++, do something like this:

class ExitException{
public:
     ExitException(int c){ m_c = c;}
     int GetCode(){ return m_c;}
private:
     int m_c;
};


...

int main(){
     try{

     /* Body of your code goes here */

     }
     catch(ExitException e){
          return e.GetCode();
     }
}


....

     /* Inside some function, and we want to exit on an unrecoverable error */
    throw ExitException(1);

That does the same sort of thing but DOES unwind the stack, and all variables going out of scope have their destructors properly called.

You could simplify this by just throwing an int to begin with, although I prefer not throwing primitives. Under that case it would look like:

int main(){
     try{

     /* Body of your code goes here */

     }
     catch(int i){
          return i;
     }
}


....

     /* Inside some function, and we want to exit on an unrecoverable error */
    throw 1;

[swgh]

Ok Cat, I think Il throw exceptions instead of using exit(0) in the future, thanks for pointing this out, I did not know about the stack issue. You learn somthing new everyday! lol
Thanks

[maxorator]

Why don't you just do this?

exit(0);

It is simple and effective

Why can't you just use

return 0;

????

[Cat]

Why can't you just use

return 0;

????

You can, if you're in main().