What are helper functions in C++?

Question

I was trying to understand what "helper functions" are in C++ from "The C++ Programming Language" by Bjarne Stroustrup. But the book hasn't explained anything about it and the purpose of using it in classes. I tried searching for it on Web and found this<\/a> [note: dead link]. I have got the gist of it but still unclear about what is the real purpose of helper functions, when should I use them and on the whole, what are helper functions?

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Answer 1

"helper function"<\/strong><\/em> is not a term that you would find in a standard, neither it has an exact definition... standard mentions "helper class"<\/em> or "helper template"<\/em> few times to refer to a class, which is not meant to be instantiated by end-users but it provides an useful functionality internally used within another class.

You can create helper functions meant to be used for many different kinds of purposes...

std::wstring s2ws(const std::string& str)
{
    int size_needed = MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), NULL, 0);
    std::wstring wstrTo( size_needed, 0 );
    MultiByteToWideChar(CP_UTF8, 0, &str[0], (int)str.size(), &wstrTo[0], size_needed);
    return wstrTo;
}

Answer 2

There is a great definition of a helper function from the CppCoreGuidline<\/a> :

Placing them in the same namespace as the class makes their relationship to the class obvious and allows them to be found by argument dependent lookup.

Answer 3

An example could be the input validation function that you will be reusing in the entire main function. Let's say you have a program that asks for the user's age, since age is an integer > 0, you'll need to have a separate function that takes care of the "cin >> users_age;". If the input satisfies the condition statement then proceed, otherwise ask the user to re-enter their age.

This is just an example of "helper function". Correct me readers if I'm wrong. Thanks!

Answer 4

"Helper functions" are described in Bjarne Stroustrups book, and I was just reading about them yesterday. According to Stroustrup good design of a class should keep the number of functions implementing a class to a minimum. You dont want to have 50 functions in a class, according to Stroustrup. Instead you use "helper functions" that use the class interface (call the member functions). They could perhaps (not sure about this) be defined in a shared namespace to give meaning to their "relationship". You can find the paragraph in the book in chapter 9 section 9.7.5

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