Question

I was playing around with strings in C++ and I don’t understand why the following causes an error when compiled:

string s = "hi";
s += " " + "there!";

Error message:

error: invalid operands of types ‘const char [2]’ and ‘const char [6]’ to binary ‘operator+’

I also tried s+= (" " + "there!"); and it doesn’t work either.

Why can’t I use the binary operator += to concatenate the strings this way?

Answer 1

The problem is you are trying to “add” two literal strings. Literal strings are not of the type std::string in C++, they are like immutable arrays of characters. Adding two together does not make sense, as it would be like adding two pointers together.

You can, however, do this:

std::string("foo") + "bar"

This is because there are methods defined in C++ to concatenate C++ strings with C strings.