General Program Flow.

[learn2adv]

My textbook yields different results from the same code entered in my program. This code is to show how objects are created.

Questions:

1. Why does my output indicate three trips to both the constructor and destructor when two were anticipated.
2. Why is the constructor visited BEFORE main() is executed?

Thanks.

// Exercise to create and delete objects using both the stack and Free Store. Also to illustrate program flow.

#include <iostream>
#include <conio.h>

using namespace std;

class Math
{
public:
Math();
~Math();
} Tom ; // optional to list the object.

Math::Math()
{
cout << "Constructor called.\n";

}

Math::~Math()
{
cout << "Destructor called.\n";
system("pause");
}


void main ()
{
cout << "Tom is created on the stack.\n";
Math Tom;
cout << "Math is created on the heap by using the new keyword.\n";
Math * pTestScore = new Math;
cout << "delete pTestScore \n";
delete pTestScore;
cout << "Exiting main(). \n";

system("pause");
}

[roberts]

class Math
{
public:
Math();
~Math();
} Tom ; // optional to list the object. 

This instantiates a global object named Tom.

void main ()
{
cout << "Tom is created on the stack.\n";
Math Tom;

This instantiates a local object named Tom.

cout << "Math is created on the heap by using the new keyword.\n";
Math * pTestScore = new Math;

This instantiates a local object that is an allocated block of memory named pTestScore because new calls constructors and delete calls destructors.

[hamsterman]

Also, globals are initialized before main is executed.

By the way, you may want to fix a few things:
main() must re int, not void.
conio.h is not a standard header and you're not even using it.

[learn2adv]

Hamsterman & Roberts:

Why is int needed when main() is not returning anything? You are correct about conio.h, it was a carryover from another program.

Thanks for your input.

[roberts]

It's a standard defined function. Some companies' compilers will allow void, but the standard main is:

int main( int argc, char *argv[] )

You don't have to do anything with argc or argv, but they're there if you want to use them.

It goes back a long way to the unix world when C programs were merely utils strung together with a shell script in assembly line fashion to process files. The utils would do their part and return a 0 or 1 or true/false to indicate success or failure.

[hamsterman]

@learn2adv, just because the standard says so. It would be a bummer if you wrote a piece of code, sent it to someone and the couldn't compile it due to something silly like this.

I should add to what roberts said that int main() is perfectly good too.

Also, note that although main has return type int, it's okay if it doesn't return anything.