通过指针调用静态成员函数

Question

I'm working on a small custom Assembler

I have a vector of struc to storing OPCODE informations (Mnemonic, number and type of argument, parsing function,...)

typedef char    args_type_t;

typedef struct  op_s {
    std::string     opcode;
    char            nbr_args;
    args_type_t     type[4];
    int             code;
    Tryte           (*fct)(std::vector<std::string>);
} op_t;

the parsing function is pointer on a static member function :

{"MOV", 2, {T_REGISTER | T_ADDRESS, T_REGISTER | T_ADDRESS | T_CONSTANT}, 1, &Opcodes::MOV},

and the function :

class Opcodes
{
public:
    static Tryte Opcodes::MOV(std::vector<std::string> _opMap) {
        return Tryte(0);
    }
};

I try this, but I get SEGFAULT ( str() is a member function of Tryte) :

for (int i = 0; i < opMap.size(); i++) {
    for (int j = 0; j < op_tab.size(); j++) {
        if (!op_tab[j].opcode.compare(opMap[i][2])) {
            std::cout << "OPBYTE : " << op_tab[j].fct(opMap[i]).str() << std::endl;
        }
    }
}

I want to call my function without instanciate Opcodes object it's posible ?

EDIT :

my error was here : if (!op_tab[j].opcode.compare(opMap[i][2])) my mnemonic is the 1st item n opMap

Answer 1

Your code seems right, so perhaps a debugger information could help a bit. But we can try to improve the friendlyness of the code by using a std::function:

typedef char    args_type_t;

#include <functional>
typedef struct  op_s {
    std::string     opcode;
    char            nbr_args;
    args_type_t     type[4];
    int             code;
    std::function<Tryte(std::vector<std::string>>)>  fct;
} op_t;

As for the sefgault, send us the backtrace. Also, try to use range-based-for as it doesn't needs to tranverse the map to get the element again (as you are doing inside of the inner loop)

for (auto op : opMap) {
    for (auto tab : op_tab) {
        if (!tab.opcode.compare(op[1])) {
            std::cout << "OPBYTE : " << tab.fct(op).str() << std::endl;
        }
    }
}

One common fix that you can do to not miss the indexes anymore is to use an Enum holding the possibilities.

enum Columns {
    FuncPointer,
    UserData
}

for (auto op : opMap) {
    for (auto tab : op_tab) {
        if (!tab.opcode.compare(op[FuncPointer])) {
            std::cout << "OPBYTE : " << tab.fct(op).str() << std::endl;
        }
    }
}