c++ - C++中没有参数可变参数模板函数

Question

template <bool ...T> 
int some_function()
{
  // this is the function with return type int
  // I am not sure how to get the values into the function
}

// this is how I want to call the function
int temp = some_function<1,0,0,0>();

对函数声明有什么建议吗？

Answer 1

对于您的用例，您可以使用递归来完成您想要的事情。为此，您需要两个重载。一个只有一个 bool(boolean) 参数，另一个带有两个 bool(boolean) 参数加上可变参数部分。这样您就可以在遍历参数包的过程中分别访问每个值。在这种情况下，

// quick and dirty pow fucntion.  There are better ones out there like https://stackoverflow.com/a/101613/4342498
template <typename T, typename U>
auto pow(T base, U exp)
{
    T ret = 1;
    for (int i = 0; i < exp; ++i)
        ret *= base;
    return ret;
}

template <bool Last>
int some_function()
{
    return Last;
}

template <bool First, bool Second, bool... Rest> 
int some_function()
{
    return First * pow(2, sizeof...(Rest) + 1) + some_function<Second, Rest...>();
}

int main()
{
    std::cout << some_function<1,0,0,0>();
}

哪个输出:

8