return char1 + char2? Isn't it possible?

Question

I'm trying to return a string from a function. Which basically adds some chars together and return the string representation.

string toString() {
   char c1, c2, c3;
   // some code here
   return c1 + c2; // Error: invalid conversion from `char' to `const char*'
}

it is possible to return boolean values like return c1 == 'x'. Isn't it possible to return string values? I know that it is possible to it like this:

string result;
result.append(c1, c2);
return result;

I'm new to C++ so I thought that there must be more elegant solution around.

Answer 1

No, you can't do that because adding two char's together doesn't give you a string. It gives you another char; in this case 'a'+'b' actually gives you '├' (on Windows with the standard CP_ACP code page). Char is an ordinal type, like integers and the compiler only knows how to add them in the most basic of ways. Strings are a completely different beast.

You can do it, but you have to be explicit:

return string(1, c1) + string(1, c2)

This will construct two temporary strings, each initialized to one repetition of the character passed as the second parameter. Since operator+ is defined for strings to be a concatenation function, you can now do what you want.

Answer 2

char types in C++ (as well as in C) are integral types. They behave as integral types. Just like when you write 5 + 3 in your code, you expect to get integral 8 as the result (and not string "53"), when you write c1 + c2 in your code above you should expect to get an integral result - the arithmetic sum of c1 and c2.

If you actually want to concatenate two characters to form a string, you have to do it differently. There are many ways to do it. For example, you can form a C-style string

char str[] = { c1, c2, `\0` };

which will be implicitly converted to std::string by

return str;

Or you can build a std::string right away (which can also be done in several different ways).