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Reputation: 5029

cast to string operator overloading in C++

I am working on a class that has a method with the following signature:

operator const std::string & () const

It's documented as "cast to string operator". I am wondering how to effectively invoke it. Unfortunately the following expression:

std::string(foo)

produces this error:

some_test.cpp:13:41: error: no matching function for call to'
std::basic_string<char>::basic_string(Foo (&)(std::string))'

Considering that foo is of type Foo, declared and instantiated as Foo foo(std::string(filename))

being a begginner of C++, this leaves me a bit confused. Any hints on what this means?

Upvotes: 0

Views: 1694

Answers (2)

Serge Ballesta
Serge Ballesta

Reputation: 148965

If you question was about the usage of operator const std::string & () const, it is quite simple : this operator is used when you need to convert to a std::string. Example :

Foo foo(filename);

std::string s = foo; // uses the declared operator const std::string & () const

Upvotes: 0

Mike Seymour
Mike Seymour

Reputation: 254501

foo is of type Foo, declared and instantiated as Foo foo(std::string(filename))

That's a function declaration, interpreting filename as the name of a function parameter, equivalent to

Foo foo(std::string filename);

A variable declaration would look like

Foo foo(filename);

or, if you needed an explicit conversion (which you probably don't here)

Foo foo{std::string(filename)};        // C++11 or later
Foo foo = Foo(std::string(filename));  // historic dialects

Upvotes: 1

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