template error

[murva]

I am trying to write this simple code to test template functionality, but I get the following error:

Error 1 error C2668: 'min' : ambiguous call to overloaded function

Could you please tell me what's wrong?Thanks

#include<iostream>
using namespace std;

template<class T>
T min(T a, T b);

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


void main()
{
	char c1='w', c2='x';
	int n1=10, n2=16;

	cout<<"min(w,x)="<<min(c1,c2)<<endl;
	cout<<"min(10,16)="<<min(n1,n2)<<endl;
}

[guestgulkan]

The STL library writers got there before you.
There is already a template function call min in the std namespace.
Choose another name for your function (or keep the name and create your own namespace for it).

[firedraco]

void main()

BADBADBADBADBAD! Use int main().

Anyway, your problem is that the function "min" is already declared on some systems. Just rename it "Min" or something.

[murva]

thanks

[jsmith]

Just to add to guestgulkan's response, #include <algorithm> will give you access to std::min() (which you are getting indirectly through iostream).

[helios]

I'd buy the C++ Committee a round of beers if they took out using.

[z05DSL3A]

I'd buy the C++ Committee a round of beers if they took out using.

using declarations or using directives, or both?

For those that don't know the difference:
using Declarations, ie:

using std::cout;
using std::cin;
using std::endl

add names to the scope in which they are declared. The effect of this is:
» a compilation error occurs if the same name is declared elsewhere in the same scope;
» if the same name is declared in an enclosing scope, the the name in the namespace hides it.

The using directive, ie using namespace std;, does not add a name to the current scope, it only makes the names accesable from it. This means that:
» If a name is declared within a local scope it hides the name from the namespace;
» a name in a namespace hides the same name from an enclosing scope;
» a compilation error occurs if the same name is made visible from multiple namespaces or a name is made visible that hides a name in the global name space.

[helios]

Both. using defeats the purpose of organizing types and functions into namespaces. What's the point if the user can just override it if he feels like it?

[z05DSL3A]

I must admit, I do hate seeing using directives, especially at global scope. It does negate the namespace concept and pulling everything from the namespace into the current scope is a bad idea.

I have less of a problem with using declarations, especially if their scope is kept restricted. Pulling names out of a namespace into the current scope can be beneficial.

Full scope resolution is desirable for production code.

As with a lot of things, if they are used to generally or without forethought, they can course problems.