Use typedef within struct for naming and indexing text commands

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甜味超标 2021-01-15 02:34

I am working with a simple command line application that takes in ASCI text and interprets it as a command.

I have attempted to minimize the redundancy in this appli

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梦毁少年i (楼主)

2021-01-15 03:11

Question:

Is there any method using the C preprocessor that would allow me to create a macro creates the "command" struct (with string and int members), and auto-numbers the int value (command_idx) as I add more commands via the COMMAND() macro?

Yes, and since you have tagged the question also as C++:

#include 
#include 
#include 
using namespace std;

map< string, int >     commands;

bool register_cmd( int id, string const& name )
{
    commands[name] = id;
    return true;
}

#define COMMAND( name ) \
    int const name ## _cmd = __LINE__; \
    bool const name ## _reg = register_cmd( name ## _cmd, #name )

COMMAND( exit );
COMMAND( help );
COMMAND( do_stuff );

int cmd_id( string const& name )
{
    auto const it = commands.find( name );
    return (it == commands.end()? -1 : it->second );
}

int main()
{
    for( auto it = commands.begin();  it != commands.end();  ++it )
    {
        cout << it->first << " => " << it->second << endl;
    }

    cout << "Gimme a command, please: ";
    string cmd;  getline( cin, cmd );
    switch( cmd_id( cmd ) )
    {
    case exit_cmd:
        cout << "You typed an EXIT command, which has id " << exit_cmd << endl;
        break;
    default:
        cout << "Hey, why not try an 'exit' command?" << endl;
    }
}

I just used map instead of fancy new C++11 hash table because map works with older compilers and no real need for shaving nano-seconds here.

Cheers & hth.,

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