Omitting arguments in C++ Templates

Question

When calling a template function, is it ok to omit the type after the function name?

As an example, consider the function

template<typename T> void f(T var){...};

Is it ok to simply call it like this:

int x = 5;
f(x);

or do I have to include the type?

int x = 5;
f<int>(x);

Answer 1

There is nothing wrong with calling it with implicit template parameters. The compiler will let you know if it gets confused, in which case you may have to explicitly define the template parameters to call the function.

Answer 2

Whenever the compiler can infer template arguments from the function arguments, it is okay to leave them out. This is also good practice, as it will make your code easier to read.

Also, you can only leave template arguments of the end, not the beginning or middle:

template<typename T, typename U> void f(T t) {}
template<typename T, typename U> void g(U u) {}

int main() {
    f<int>(5);      // NOT LEGAL
    f<int, int>(5); // LEGAL

    g<int>(5);      // LEGAL
    g<int, int>(5); // LEGAL

    return 0;
}