Here is the minimal reproducible code,
#include <iostream>
#include <string>
void bar(std::string s, int x){
std::cout <<std::endl<< __FUNCTION__<<":"<<s<<" "<<x;
}
using f_ptr = void(*)(std::string);
void foo(f_ptr ptr){
ptr("Hello world");
}
template<typename T> void fun(T f){
static int x;
std::cout <<std::endl<<x++<<std::endl;
f("Hello World");
}
int main()
{
//case:1
f_ptr ptr1 = [](std::string s){bar(s,10);};
// foo(ptr1);
//case:2
static int x =10;
f_ptr ptr2 = [x](std::string s){bar(s,x);};
//foo(ptr2);
//case:3
int y =10;
f_ptr ptr3 = [y](std::string s){bar(s,y);}; /* error*/
foo(ptr3);
//case:4
int z = 12;
fun([z](std::string s){bar(s,z);});
return 0;
}
Error:
main.cpp:25:50: error: cannot convert ‘main()::’ to ‘f_ptr {aka void (*)(std::basic_string)}’ in initialization
f_ptr ptr3 = [y](std::string s){bar(s,y);}; /* error*/
My questions are,
- Is there any way to forwards additional arguments like
case:3
via lambda? - What conversion is causing error in
case:3
? - In
case:4
,typename T
is deduced to what?
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