how to initialize function arguments that are classes with default value

问题

I'm working on Linux gcc environment and I need to initilize function arguments that are classes with default values. When I do that with temporary instance of the class it makes an error like this: "default argument for [function argument] has type [class name]. for example:

void foo(std::wstring& str = std::wstring())

error: default argument for 'std::wstring& str' has type 'std::wstring' P.S. this code is compiled without any error or warning with VC++.

How can I initilize the default value?

回答1:

This is supposed to not compile. You are trying to bind an rvalue to a non-const reference. Say std::wstring const & str and it should work.

回答2:

You could just create a function overload:

void foo() {
    std::wstring str;
    foo(str);
}

but I really miss the point.

EDIT: I mean, that function's purpose is almost certainly to modify an input string. If you provide an empty input string that you can't access later, why bother?

回答3:

You cannot bind non-const references to rvalues. Passing by value would work:

void foo(std::wstring str = std::wstring())

Or passing by reference-to-const:

void foo(const std::wstring& str = std::wstring())

来源：https://stackoverflow.com/questions/4238141/how-to-initialize-function-arguments-that-are-classes-with-default-value