Can I give a c++ function a custom symbol name? - c++

Question

I want to give a c++ function a custom symbol name (without mangling) so that a can call it from c directly without redirection. For example: If I have the following class in c++:
class Foo {
public:
Foo();
void some_method(int);
int a_;
};
I want to give Foo::some_method a custom name like Foo_some_method so that I can call it from c code directly without need for redirection from another function inside extern "C", is that possible?

Answer 1

No, to enable a C conpatible calling convention and symbol name you need to produce an extern "C" normal function (in theory, an extern "C" function pointer could also work).
So write your glue code.
It is plausible with reflection you'll be able to automate that. But that is not yet standardized, and covid 19 may delay it past 2023.

Answer 2

I tested this using g++ and gcc and it worked! I used asm labels to give the symbol a custom name.
product.h
#ifndef BCC702_PRODUTO_H
#define BCC702_PRODUTO_H
#include <string>
#include <ostream>
class product {
public:
/// Create product
product(int id, double price, char* name);
/// Print product
void print() asm("Asm_product_print");
void set_name(char* name) asm("Asm_product_set_name") ;
private:
int id_;
double price_;
char* name_;
};
#endif //BCC702_PRODUTO_H
product.cpp compiled to object using g++
#include "product.h"
#include <iostream>
void product::print() {
std::cout << name_ << std::endl;
}
product::product(int id_, double price_, char* _name_) :
id_(id_), price_(price_), name_(_name_) {}
void product::set_name (char* _name_) {
product::name_ = _name_;
}
main.c compiled with gcc
typedef struct{
int id_;
double price_;
char* name_;
} product;
void Asm_product_set_name(product* p, char* string);
void Asm_product_print(product* p);
char* example = "hello world!";
int main(){
product p;
Asm_product_set_name(&p, example);
Asm_product_print(&p);
return 0;
}
Finally, link objects using g++. And the test result is:
Hello world!
However, I'm not sure whether it will work with other c++ compilers.