On Wed, 18 Aug 2004 16:09:02 +0000 (UTC), Christopher Benson-Manica
<ataru@nospam.cyberspace.org> wrote:
[color=blue]
>Is my implementation correct to print only a blank line when the
>following program is compiled and run?
>
>#include <iostream>
>#include <map>
>
>int main()
>{
> std::map< const char *, std::string > m;[/color]
Ok, so your map is flawed already - you can't < compare pointer values
unless those pointers point into the same object (or array).
[color=blue]
> m["foo"]="bar";
> std::cout << m["foo"] << std::endl;[/color]
The second "foo" may or may not have the same address as the first one
- it's unspecified. So that may or may not have undefined behaviour
(which is what you're seeing).
[color=blue]
> return 0;
>}
>
>g++ prints "bar", which is of course the behavior I want. If this is
>a(nother) problem with my implementation, what, if anything, can I do
>to work around it?[/color]
I think you way to have the map sorted according to the contents of
the string, not the pointer value? If so, then you need something
like:
#include <cstring>
struct strcmper
{
typedef bool result_type;
typedef const char* first_argument_type;
typedef const char* second_argument_type;
bool operator()(const char* lhs, const char* rhs) const
{
return std::strcmp(lhs, rhs) < 0;
}
};
//...
std::map< const char *, std::string, strcmper > m;
Tom
