c++ - call of overloaded 'swap(char&, char&)' is ambiguous -

i can't figure out ambiguous swap(arr[i++],arr[n--]); below. please educate me on wrongful ways.

#include <iostream> #include <string>  template <typename t> void swap ( t & a, t & b ) {     t temp = b;     b = a;     = temp; }  template <typename t> void reverse_array ( t * arr, size_t n ) {    size_t = 0;    while (i < n) swap(arr[i++],arr[n--]); // problem line }   int main ()  {    char mystr [] = "obama smokes";    reverse_array(mystr, sizeof(mystr)/sizeof(char));    return 0; } 

codepad has implicit using namespace std;, bad idea , makes swap conflict std::swap. can use ::swap instead, not before fixing bounds problem passing sizeof mystr - 2 instead of sizeof(mystr)/sizeof(char).