From: "A. Sinan Unur" <asu1 AT cornell DOT edu>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Can You help me about djgpp with c++
Date: 10 Sep 2001 23:28:22 GMT
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"Gorden" <gorden AT ms9 DOT url DOT com DOT tw> wrote in
news:003201c13a3f$053b2f40$aa7ba8c0 AT fuego: 

> I Buy a book (Teach Yourself C++, 3rd Edition By Herbert Schildt) 
> inside have a C++ smaple

I modified your code as follows:

#include <iostream>

class Sample
{
  private:
    int i;

  public:
     Sample()   { std::cout << "Constructor" << std::endl; }
	 
	 Sample(const Sample& src) 
	 { 
		 i = src.i;
		 std::cout << "Copy constructor" << std::endl;
	 }

	 Sample& operator=(const Sample& rhs)
	 {
		 if( &rhs != this )
		 {
			 i = rhs.i;
		 }

		 std::cout << "Assignment operator" << std::endl;

		 return *this;
	 }
	 
    ~Sample()   { std::cout << "Destructor " << std::endl; }
	
    void set(int n) {  i = n ;  }
    int  get(void ) { return i; }

};

int test(Sample o)
{
  return o.get() * o.get();
}

int main(void)
{
  Sample aSample;
  aSample.set(10);
  std::cout << test(aSample) << std::endl;

  return 0;
}

When compiled and run, this code produces the following:

C:\var>gpp t.cc -o t.exe -Wall

C:\var>t
Constructor
Copy constructor
Destructor
100
Destructor

You can see that your original code was missing the copy constructor, and 
the compiler was creating an extra copy for the test function call. 
Incidentally, compiling your original code with -O3 gets rid of this extra 
copy.

I guess the compiler, in the absence of aggressive optimization or a copy 
constructor is creating am extra temporary.

Sinan.
-- 
--------------------------------
A. Sinan Unur
http://www.unur.com/