variadic templates & pass by const reference & member operator [] in const map & gcc suc
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/// bugs code with comments
#include <iostream>
#include <memory>
#include <unordered_map>
using namespace std;
class A
{
public:
A(const std::unordered_map<int, int > &ref) : ref_m(ref) {}
void test1(int index) {
// std::cout << ref_m[index] << std::endl; // bugs version in c++ specification, mainly sucks in gcc compile error prompts.
std::cout << ref_m.at(index) << std::endl; // or ref_m.find() etc.
}
// this function will crash, as a result of ref_m get a wrong memory address by value passing instead of reference passing in gcc
void test2() {
for(auto& e: ref_m)
std::cout << e.first << ‘ ‘<< e.second << std::endl;
}
void print_ref_size() {
std::cout << "ref_m size: " << ref_m.size() << std::endl;
}
private:
const std::unordered_map<int, int >& ref_m;
};
template <typename ManipulatorType, typename ... Args>
std::shared_ptr<ManipulatorType> CreateTester(std::string name, Args ... args)
{
return std::make_shared<ManipulatorType>(args ...);
}
class B{
public:
B(){}
std::shared_ptr<A> CreateATesterWrapper() {
// return CreateTester<A>("uselessparams", ref); // bugs version in gcc
return CreateTester<A>("uselessparams", std::ref(ref)); // or replace "Args ... args" with "Args& ... args" in gcc
}
void print_ref_size() {
std::cout << "ref size: " << ref.size() << std::endl;
}
std::unordered_map<int, int > ref = {{1,2}};
};
int main(int argc, char* argv[])
{
B b;
auto a = b.CreateATesterWrapper();
b.print_ref_size();
a->print_ref_size();
a->test1(1);
a->test2();
return 0;
}
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