找不到使用位集实例化模板函数的有效方法

以下代码对我有效。在VS2017和G++7.3上编译

// 
// bit_tools.h
// 
#include <bitset>

template <size_t sizeA, size_t sizeB, size_t sizeAB>
std::bitset<sizeAB> join2(std::bitset<sizeA> bsetA,
                           std::bitset<sizeB> bsetB);

// 
// bit_tools.cc
// 
#include "bit_tools.h"

template <size_t sizeA, size_t sizeB, size_t sizeAB>
std::bitset<sizeAB> join2(std::bitset<sizeA> bsetA, std::bitset<sizeB> bsetB) {
    return std::bitset<sizeAB>(bsetA.to_string() + bsetB.to_string());
}

// Here you should provide integer constants instead of type
template
std::bitset<32>  join2<16,16,32>(std::bitset<16> bsetA, std::bitset<16> bsetB);

// 
// main.cc
// 

#include "bit_tools.h"

int main() {

    std::bitset<16> bsetA;
    std::bitset<16> bsetB;

    join2<16,16,32>(bsetA, bsetB);
}