swap fails in case of int and works in case of string
#include <iostream>
#include <string>
#include <algorithm>
int main()
{
std::string str1 = "good", str2 = "luck";
swap(str1,str2); /*Line A*/
int x = 5, y= 3;
swap(x,y); /*Line B*/
}
If I comment Line B开发者_开发知识库 the code compiles(http://www.ideone.com/hbHwf) whereas commenting Line A the code fails to compile(http://www.ideone.com/odHka) and I get the following error:
error: ‘swap’ was not declared in this scope
Why don't I get any error in the first case?
swap(str1, str2)
works because of Argument dependent lookup
P.S: Pitfalls of ADL
You're not qualifying swap
; it works when passing in std::string
objects because of ADL, but as int
does not reside in namespace std
you must fully qualify the call:
std::swap(x, y);
or use a using declaration:
using std::swap;
swap(x, y);
strings are in the std:: namespace, so the compiler looks for swap() for strings there. ints are not, so it doesn't. You want:
std::swap(x,y);
In both cases you should be using std::swap()
instead of swap()
.
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