Call static member function by pointer

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

Try (op_tab[j].fct)(opMap[i]).str(). The braces are important for grouping, since fct is a pointer to a function, not a member function. — Peter
– Peter, Commented Apr 5, 2017 at 10:00
thx, but I found my problem : !op_tab[j].opcode.compare(opMap[i][2]) in my opMap the mnemonic is at place 1 not 2 >< — Jeremy Talus
– Jeremy Talus, Commented Apr 5, 2017 at 10:03

Tomaz Canabrava · Accepted Answer · 2017-04-05 10:11:38Z

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; } } }

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