templates

[mickey]

Hello, I have some question:

template<class T>
void swap(T* a, T* b) {
	T temp = *a;
	*a = *b;
	*b = temp;
}
int x,y;
swap(&x,&y);
swap(x,y); //why this compile and it works?

template<class T>
void swap(T* a, T* b) {
	T temp = *a;
	*a = *b;
	*b = temp;
}
int x,y;
swap(&x,&y);
swap(x,y); //why this compile and it works?

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template<class T>
void swap(T* a, T* b) {
	T* temp = *a;
	*a = *b;
	*b = temp; // *b = *temp; /*with this same problem  before */
}
int x,y;
swap(&x, &y); //why now this doens't compile?
swap(x, y); // why this compile

template<class T>
void swap(T* a, T* b) {
	T* temp = *a;
	*a = *b;
	*b = temp; // *b = *temp; /*with this same problem  before */
}
int x,y;
swap(&x, &y); //why now this doens't compile?
swap(x, y); // why this compile

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For what I knew, with void swap(T* a, T* b), should only work swap(&x, &y);

Thanks in advance.

[marcel]

Compiling with msvc, right?
You don't get any error because the compiler uses this function instead, defined in include/utility.

template<class _Ty> inline
    void swap(_Ty& _Left, _Ty& _Right)
    {    // exchange values stored at _Left and _Right
    if (&_Left != &_Right)
        {    // different, worth swapping
        _Ty _Tmp = _Left;
 
        _Left = _Right;
        _Right = _Tmp;
        }
    }

template<class _Ty> inline
    void swap(_Ty& _Left, _Ty& _Right)
    {    // exchange values stored at _Left and _Right
    if (&_Left != &_Right)
        {    // different, worth swapping
        _Ty _Tmp = _Left;

        _Left = _Right;
        _Right = _Tmp;
        }
    }

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Rename your function and you'll see the errors.

[jacek]

Do you have "using namespace std" anywhere in your source code?

[mickey]

Do you have "using namespace std" anywhere in your source code?

yes, I have only main.cpp and I have using namespace std;
But with Marcel hint, I solve every problem....but for me this is strange! Something more about avoid this problem? (apart change name to functions)
It gets me the same error with:

template<class T> 
T min(const T& a, const T& b ) {  
  if( a < b )
    return( a ) ;
  else
    return( b ) ;
}

template<class T> 
T min(const T& a, const T& b ) {  
  if( a < b )
    return( a ) ;
  else
    return( b ) ;
}

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but change to 'mymin' everything seems to work....

[marcel]

Yes, these functions are already defined in utility.h, which gets included before your header.
Try defining your functions in a separate namespace and access them with the scope resolution operator(myNameSpace::min or myNameSpace::swap).

[jacek]

yes, I have only main.cpp and I have using namespace std;

You wouldn't have such problems without that line. It's better to use std:: prefix for all functions and classes from standard namespace.