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Class lookup structure array in C++

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花落未央
花落未央 2021-01-16 11:51

I\'m trying to create a structure array which links input strings to classes as follows:

struct {string command; CommandPath cPath;} cPathLookup[] = {
    {\
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  • 滥情空心
    滥情空心 (楼主)
    2021-01-16 12:34

    Personally I don't see it as being a huge problem if you just have 1 factory for creating different "CommandPaths" for different values of the string it receives. Anyway, your code won't work because you can't store types the way you're trying.

    If I had to do this, then for one I would use function pointers to factory functions and use a std::map to map strings to these, like shown in this code, and maybe wrap the pointers in an appropriate smart-pointer, instead of using raw pointers:

    #include 
#include 

struct A {
};

struct B : public A {
};

struct C : public A {
};

A *BFactory(){
    return new B();
}

A *CFactory(){
    return new C();
}

typedef A *(*Factory)();
typedef std::pair Pair;
typedef std::map Map;

Pair Pairs[] = 
{
    std::make_pair( "alarm", BFactory ),
    std::make_pair( "email", CFactory )
};

Map Lookup( Pairs, Pairs + sizeof(Pairs)/sizeof(*Pairs) );

A *CreateInstance( const std::string &Type )
{
    Map::const_iterator i = Lookup.find( Type );

    if( i != Lookup.end() )
        return i->second();
    else
        return 0;
}

    As for your question about pointers and abstract classes, you can have a pointer to an abstract class, but you can't instantiate an abstract class.

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