Re: Trying to call a function pointer causes a compile error with GNU G++

Hi,

I've got this class that parses command line input, which won't
compile, the error message is:

% g++ buggy.cpp -o buggy
buggy.cpp: In member function ???int Command::execute()???:
buggy.cpp:110: error: must use ???.*??? or ???->*??? to call pointer-to-member
 function in ???((Command*)this)->Command::cmd.
 std::_Rb_tree_iterator<_Tp>::operator-> [with _Tp = std::pair<const
 Command::ELEMENT, int>]()->std::pair<const Command::ELEMENT,
 int>::first.Command::ELEMENT::function (...)???

And the code itself is as follows (I've simply boiled it down to a
short 124 line program) I'd be grateful if you can point out what I'm
doing wrong when calling via Command::execute(), many thanks!

#include <iostream>
#include <map>
#include <vector>
#include <string>
#include <cassert>

class Command
{
public:
    Command(std::vector<std::string>& arguments);
    ~Command();

    int execute();

    struct ELEMENT
    {
    public:
        bool operator==(const ELEMENT& rhs) const
        {
            return (strcasecmp(command.c_str(), rhs.command.c_str()) == 0);
        }

        bool operator<(const ELEMENT& rhs) const
        {
            return (strcasecmp(command.c_str(), rhs.command.c_str()) != 0);
        }

        friend std::ostream& operator<<(std::ostream& os, const ELEMENT& rhs);

        std::string command;
        int (Command::*function)();

     };

private:
    int a(void);
    int b(void);
    int c(void);

    static const int COMMANDS;
    static const ELEMENT command_table[];

    std::map<ELEMENT, int>* commands;
    std::map<ELEMENT, int>::iterator cmd;
};

const int Command::COMMANDS = 3;
const Command::ELEMENT Command::command_table[Command::COMMANDS] =
{
    { "a", &Command::a },
    { "b", &Command::b },
    { "c", &Command::c }
};
[...]

int Command::execute()
{
    if (cmd->first.function != NULL)
        return (cmd->first.function)();

     return -1;
}

int main(int argc, char* argv[])
{
    std::vector<std::string> arguments;
    for (int i = 1; i < argc; i++)
        arguments.push_back(argv[i]);

    Command command(arguments);
    command.execute();
}