Variadic template not compiled [duplicate] - c++

Question

This question already has answers here:
Cannot have typeof(std::endl) as template parameter?
(2 answers)
Closed 9 years ago.
Code:
#include <iostream>
template<typename T>
void out() // line 4
{
}
template<typename T, typename... Args>
void out(T value, Args... args) // line 9
{
std::cout << value;
out(args...); // line 12
}
int main()
{
out("12345", std::endl); // line 17
return 0;
}
Build errors:
g++ -O0 -g3 -Wall -c -fmessage-length=0 -std=c++11 -pthread -MMD -MP -MF"main.d" -MT"main.d" -o "main.o" "../main.cpp"
../main.cpp: In function ‘int main()’:
../main.cpp:17:24: error: no matching function for call to ‘out(const char [6], <unresolved overloaded function type>)’
../main.cpp:17:24: note: candidates are:
../main.cpp:4:6: note: template<class T> void out()
../main.cpp:4:6: note: template argument deduction/substitution failed:
../main.cpp:17:24: note: candidate expects 0 arguments, 2 provided
../main.cpp:9:6: note: void out(T, Args ...) [with T = const char*; Args = {}]
../main.cpp:9:6: note: candidate expects 1 argument, 2 provided
I want this program to give the same result as std::cout << "12345" << std::endl; What is wrong in the template function?

Answer 1

The problem is that you made your no argument version of out be a template, and it cannot be called without explicitly supplying template arguments. Thus
void out() {}
template<typename T, typename... Args>
void out(T value, Args... args) {
std::cout << value;
out(args...);
}
int main() {
out(1, 2.0, "3");
return 0;
}
works as intended.

Answer 2

There is a syntax error (a missning .) that makes the compiler go crazy.
After that, you may also have a problem with the out("12345", std::endl) call, being std::endl an overridden function that compiler cannot choose from (just cast it as static_cast<std::ostream&(*)(std::ostream&)>(std::endl))
Also, the recursion in out ends in a out() call, but there is no out with 0 parameters.(see also yuri answer: https://stackoverflow.com/a/20879525/924727 )