"Prakash Bande" <prakash.bande@altair.com> wrote in message
news:dd3e7aa8.0408182356.636b8d8e@posting.google.c om...[color=blue]
> Hi,
> I have bool operator == (xx* obj, const string st). I have declared it
> as friend of class xx. I am now able to do this:
> xx ox;
> string st;
> if (&ox == st)
> {
> }
> But, when I have a vector<xx*> and use stl find
> string xyz;
> vector<xx*>::iterator i = find(ii, xv.end(), xyz);
>
> c:\program files\include\algorithm(43) : error C2679: binary '==' : no
> operator defined which takes a right-hand operand of type 'const class
> std::basic_string<char,struct std::char_traits<char>,class
> std::allocator<char> >' (or there is no acceptab
> le conversion)
>
> Here is a code snippet:
>
> #include "stdafx.h"
> #include <string>
> #include <vector>
> #include <iostream.h>
> using namespace std;
> class xx;
> bool operator == (xx* obj, const string st);
> #include <algorithm>
>
> class xx
> {
> friend bool operator == (xx* obj, const string st);
> private:
> string ab;
> int i;
> public:
> xx(string a);
> };
>
> xx::xx(string a)
> {
> ab = a;
> }
> bool operator == (xx* obj, const string st)
> {
> if (st == obj->ab)
> return true;
> return false;[/color]
type of (st == obj->ab) is bool so
return (st == obj->ab) ;
is enough
[color=blue]
> }
>
> int main(int argc, char* argv[])
> {
> printf("Hello World!\n");
> vector<xx*> xv;
> xx x1("some1");
> xv.push_back(&x1);
> xx x2("some2");[/color]
I think you forgot to add
xv.push_back(&x2);
[color=blue]
> vector<xx*>::iterator ii = xv.begin();
> string xyz = "some2";
> if (*ii == xyz )
> {
> }
> while (ii != xv.end())
> {
> vector<xx*>::iterator i = find(ii, xv.end(), xyz);
> xx *f = *i;
> ii = i;
> ii++;
> }
> }[/color]
Very interesting, it compiles without a problem on VC7.1 but fails on VC6,
which I assume you're using.
No idea why, and it is not restricted to find. VC6 refuses to compile when
you have global operator ==
where the first argument is not a struct/class.
for example
bool operator == (int i, const string &){ return false; }
int ints[] = { 1, 2, 3, 4 };
size_t cnt = count(ints, ints+4, string("aaa"));
fails, whereas
bool operator == (const string &, int i){ return false; }
string strings[] = { "a", "b", "c", "d" };
size_t cnt = count(strings, strings+4, 5);
compiles
To go back to your problem... this works:
instead of operator== use binary predicate
struct xx_equal : public ::std::binary_function<xx*, ::std::string,
bool>
{
bool operator()(xx * obj, const ::std::string & st) const
{
/*1*/ return (st == obj->ab);
************
VC6 doesn't complain if you use your original operator == here
************
return obj == st;
}
};
then use find_if instead of find
#include <functional> // for bind2nd
vector<xx*>::iterator i = find_if(ii, xv.end(), bind2nd(xx_equal(),
xyz));
you can declare xx_equal a friend of xx or even better declare accessor
function in xx for ab like
// inside xx
const string & get_ab() const { return ab; }
and instead of /*1*/ use
return (st == obj->get_ab());
VZ
