指向类方法的C ++指针

Question

I want to do something like this:

struct CLI_Command{
    CLI_Command(char* s, void (*h)(void)){
        command_string = s;
        handler = h;
    }

    char* command_string;
    void (*handler)(void);
};

class CLI  {
    public:
        CLI();

    private:
        CLI_Command cli_table[NO_CLI_COMMANDS] = {
                CLI_Command("Command1",   handler1),
                CLI_Command("Command2",   handler2)
        };

        void handler1(){};
        void handler2(){};
};

I know that I need something similar to CLI::*handler, but I can't get the syntax right. I keep running into errors like this:

"error: no matching function for call to 'CLI_Command::CLI_Command(const char [4], <unresolved overloaded function type>)"

Answer 1

This illustrates the correct syntax:

class CLI;

struct CLI_Command
{
    CLI_Command(char* s, void (CLI::*h)(void))
    {
        command_string = s;
        handler = h;
    }

    char* command_string;
    void (CLI::*handler)(void);

    void raise( CLI* the_cli ) { return (the_cli->*handler)(); }
};

class CLI
{
    public:
        CLI();

    private:
        static CLI_Command cli_table[NO_CLI_COMMANDS];

        void handler1(){};
        void handler2(){};
};

CLI::CLI_Command cli_table[NO_CLI_COMMANDS] = {
  { "Command1",   &CLI::handler1 },
  { "Command2",   &CLI::handler2 }
};

Names of member functions do not decay to pointer-to-member. You must use & explicitly, and a qualified name, when creating a pointer-to-member.

Answer 2

In addition to other answers, another option is to use std::function together with std::bind() :

struct CLI_Command{
    ...
    std::function<void> handler;
};

class CLI {
    ...
    CLI_Command cli_table[NO_CLI_COMMANDS] = {
      { "Command1",   std::bind(&CLI::handler1, this) },
      { "Command2",   std::bind(&CLI::handler2, this) }
    };

    void handler1(){};
    void handler2(){};
};

Answer 3

void handler1(){}
void handler2(){}

are member functions of CLI . The correct way to "address to" them is &CLI::handler1 and not handler1 . However then, they won't be accepted by void (*h)(void) , which would need to be changed to void (CLI::*h)(void) . But that is probably not what you want.

Maybe consider reading about std::function for type erasure, or make your handler1/handler2 static.

Answer 4

You should use the syntax for a pointer to class member instead of the syntax for a loose function pointer.

class CLI;

struct CLI_Command{
    CLI_Command(char* s, void (CLI::*h)(void)){
        command_string = s;
        handler = h;
    }

    char* command_string;
    void (CLI::*handler)(void);
};

In addition, make sure you call the function through the pointer of the current CLI class;

void CLI::process(char *cmd) {
    CLI_Command command* = /* lookup the command */
    this->(command->handle)();
}

Answer 5

To get it working, make your methods static

static void handler1(){};
static void handler2(){};

Whatever consequences ( read here please, for more detailed info) this will have :-( .