ambiguous call in template error - c++

Question

Can anyone tell me the cause of error ?
Error is
C:\web\template1.cpp||In function 'int main()':|
C:\web\template1.cpp|23|error: call of overloaded 'swap(int&, int&)' is ambiguous|
C:\web\template1.cpp|6|note: candidates are: void swap(X&, X&) [with X = int]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\move.h|76|note: void std::swap(_Tp&, _Tp&) [with _Tp = int]|
C:\web\template1.cpp|24|error: call of overloaded 'swap(double&, double&)' is ambiguous|
C:\web\template1.cpp|6|note: candidates are: void swap(X&, X&) [with X = double]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\move.h|76|note: void std::swap(_Tp&, _Tp&) [with _Tp = double]|
C:\web\template1.cpp|25|error: call of overloaded 'swap(char&, char&)' is ambiguous|
C:\web\template1.cpp|6|note: candidates are: void swap(X&, X&) [with X = char]|
c:\program files\codeblocks\mingw\bin\..\lib\gcc\mingw32\4.4.1\include\c++\bits\move.h|76|note: void std::swap(_Tp&, _Tp&) [with _Tp = char]|
||=== Build finished: 3 errors, 0 warnings ===|
#include <iostream>
using namespace std;
template <typename X>
void swap(X &a, X &b)
{
X temp = a;
a = b;
b = temp;
}
int main()
{
int i=10, j=20;
double x=10.1, y=23.3;
char a='x', b='z';
cout<<"i="<<i<<"\tj="<<j<<endl;
cout<<"x="<<x<<"\ty="<<y<<endl;
cout<<"a="<<a<<"\tb="<<b<<endl;
swap(i,j);
swap(x,y);
swap(a,b);
cout<<"i="<<i<<"\tj="<<j<<endl;
cout<<"x="<<x<<"\ty="<<y<<endl;
cout<<"a="<<a<<"\tb="<<b<<endl;
return 0;
}

Answer 1

Your swap conflicts with std::swap. Remove using namespace std; above and correct the rest code from std namespace.
std::cout<<"i="<<i<<"\tj="<<j<<std::endl;
std::cout<<"x="<<x<<"\ty="<<y<<std::endl;
std::cout<<"a="<<a<<"\tb="<<b<<std::endl;
Also it's worth reading Why is "using namespace std" considered bad practice?

Answer 2

Rename swap() as swap2() or the like. Or, better, never issue using namespace std;.
As written, your code introduces std::swap() through iostream, then dumps it atop your own swap() by using namespace.

Answer 3

There is already a swap function declared somewhere in your code. Change the function's name or remove the declaration of the other swap function.

Answer 4

This ambiguous errors occur due to using std functions as general functions.
There are two ways to overcome this.
1) Instead of declaring using namespace std; use std::cout
whenever you need to print any and std::endl for new line.
#include <iostream>
template <typename X>
void swap(X &a, X &b)
{
X temp = a;
a = b;
b = temp;
}
int main()
{
int i=10, j=20;
double x=10.1, y=23.3;
char a='x', b='z';
std::cout<<"i="<<i<<"\tj="<<j<<std::endl;
std::cout<<"x="<<x<<"\ty="<<y<<std::endl;
std::cout<<"a="<<a<<"\tb="<<b<<std::endl;
swap(i,j);
swap(x,y);
swap(a,b);
std::cout<<"i="<<i<<"\tj="<<j<<std::endl;
std::cout<<"x="<<x<<"\ty="<<y<<std::endl;
std::cout<<"a="<<a<<"\tb="<<b<<std::endl;
return 0;
}
2) You can also change the swap to Swap to not conflict with the inbuilt std::swap function.
#include <iostream>
using namespace std;
template <typename X>
void Swap(X &a, X &b)
{
X temp = a;
a = b;
b = temp;
}
int main()
{
int i=10, j=20;
double x=10.1, y=23.3;
char a='x', b='z';
cout<<"i="<<i<<"\tj="<<j<<endl;
cout<<"x="<<x<<"\ty="<<y<<endl;
cout<<"a="<<a<<"\tb="<<b<<endl;
Swap(i,j);
Swap(x,y);
Swap(a,b);
cout<<"i="<<i<<"\tj="<<j<<endl;
cout<<"x="<<x<<"\ty="<<y<<endl;
cout<<"a="<<a<<"\tb="<<b<<endl;
return 0;
}