c++ - Why can't the compiler resolve an overload of a std::function parameter? -

this question has answer here:

• wrap overloaded function via std::function 1 answer

observe following example:

#include <iostream> #include <functional> #include <cstdlib>  void print_wrapper(std::function<void(int)> function); void print(int param);  int main(){    print_wrapper(print);    return exit_success; }  void print_wrapper(std::function<void(int)> function){   int = 5;   function(i); } void print(int param){   std::cout << param << std::endl; } 

this works correctly, , prints 5.

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now @ same example overloaded function added:

#include <iostream> #include <functional> #include <cstdlib>  void print_wrapper(std::function<void(int)> function); void print(int param); void print(float param);  int main(){    print_wrapper(print);    return exit_success; }  void print_wrapper(std::function<void(int)> function){   int = 5;   function(i); } void print(int param){   std::cout << param << std::endl; } void print(float param){   std::cout << param << std::endl; } 

this gives following compiler error:

main.cpp:11:22: error: cannot resolve overloaded function ‘print’ based on conversion type ‘std::function’
print_wrapper(print);

could explain why compiler can't resolve overload?
print_wrapper expects int function-- float function shouldn't considered.

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additionally, should fix this?

i recall problems occurring if typename or left out, require me make print_wrapper template.
print_wrapper need function template?

i guess i'm use functionality similar this, works. example:

#include <iostream> #include <vector> #include <cstdlib>  void print_wrapper(std::vector<int> param); void print(std::vector<int> param); void print(std::vector<float> param);  int main(){    std::vector<int> vi{1,2,3};   std::vector<float> vf{1.0,2.0,3.0};    print(vi); //prints int   print(vf); //prints float    print_wrapper(vi); //prints int (no overload issue)   print_wrapper(vf); //compiler error (as expected)    return exit_success; }  void print_wrapper(std::vector<int> param){   print(param);   return; } void print(std::vector<int> param){   std::cout << "int" << std::endl; } void print(std::vector<float> param){   std::cout << "float" << std::endl; } 

so think issue lies somewhere in lookup rules of actual c++ function, example uses types. thoughts?

in c++11, std::function's constructor can take callable object, when ill-formed , cannot call object. in c++14, overload resolution fixed both functions can called int both valid candidates.

you need explicitely request correct function:

print_wrapper(static_cast<void(*)(int)>(print))