C++ overloading + operator in order to always concatenate strings of every kind

Question

It's very pointless and troublesome that everytime that you need to concatenate two strings it is necessary to do at least:

std::string mystr = std::string("Hello") + " World";

I would like to overload operator+ and use it in order to always do a concat between tho char* in this way:

std::string mystr = "Ciao " + "Mondo".

How would you do? I'd like to find a best practice. Thank you...

Ah does boost have something to solve this?

You know, one question mark is sufficient in order to indicate that something is a question. Using six of them in a row does not make it any more of a question. Unless your cat sat on the keyboard, there's no reason for it. — jalf, Dec 06 '10 at 12:27
STL string concatenation best practices: http://stackoverflow.com/questions/611263/efficient-string-concatenation-in-c — Bojan Komazec, Dec 06 '10 at 12:41

score 5 · Accepted Answer · answered Dec 06 '10 at 12:25

5

You cannot make + work like this. To define an operator overload, at least one of the operands must be a user-defined type.

However, the functionality is built in: if you just put two string literals together "like" "this", they will automatically be joined together at compile time.

answered Dec 06 '10 at 12:25

Karl Knechtel

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@Andry: Why would you want to type `"Hello" + "World"` when `"Hello" "World"` (a) is shorter to type and (b) works? – CB Bailey Dec 06 '10 at 12:35
@Andry that's just what I finished saying in the first part. Notice, in the second part, that there is no `+` in `"like" "this"`. – Karl Knechtel Dec 06 '10 at 12:50

score 2 · Answer 2 · answered Dec 06 '10 at 12:25

2

You can't. There is no way to overload operators between built-in types. I'm also not sure why it's so "troublesome". If you do a lot of string operations, then surely one or both parameters will already be of type std::string.

answered Dec 06 '10 at 12:25

jalf

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score 1 · Answer 3 · edited May 23 '17 at 10:33

You can't. Think about it - what is "Ciao " and "Mondo", really? They are static arrays of characters. You can't add static arrays together, as the compiler will helpfully point out for the following code:

#include <iostream>

int main()
{
  std::string mystr = "Ciao " + "Mondo";
  std::cout << mystr << std::endl;
  return 0;
}

(output:

In function 'int main()':
Line 5: error: invalid operands of types 'const char [6]' and 'const char [6]' to binary 'operator+'

That's it. This is pretty much a dupe of: const char* concatenation.

C++ overloading + operator in order to always concatenate strings of every kind

3 Answers3