How to make a function that can be called on an object the same way as the member functions for that class? [duplicate]

Question

For example, if you have an object of the std::string class, you can call the compare(string str) function as follows:

myString.compare(myOtherString);

How can I make my own function that I can call on a string in the same way? Example:

myString.contains(char[] chars);

@PiotrS.: I get the sense that that's the question OP is trying to ask. — John Dibling
– John Dibling, Commented Sep 9, 2014 at 12:26
If you're asking if you can add to an existing, closed, class definition, no, you can't. — WhozCraig
– WhozCraig, Commented Sep 9, 2014 at 12:27

Mike Seymour · Accepted Answer · 2014-09-09 12:28:59Z

1

You can't add member functions to existing classes in C++. Instead, write a non-member function

bool contains(std::string const & s1, std::string const & s2);

and call it as

contains(myString, myOtherString);

answered Sep 9, 2014 at 12:28

Mike Seymour

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John Zwinck · Accepted Answer · 2014-09-09 12:28:39Z

0

You can't really do this in C++, and you shouldn't try. Sure, you could inherit from std::string and implement your methods, but then your methods will be unusable from regular strings. In C++ we do not try too hard to make everything a class method--free functions are functions too!

answered Sep 9, 2014 at 12:28

John Zwinck

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1 Comment

Mike Seymour Over a year ago

You could try, and end up with something like slideshare.net/phil_nash/c-extension-methods-18678294. But don't do this at home.

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