Why `std::string`'s assignment operator take `char` by value and not `const` reference?

Question

Accidentally I came across below situation:

int i = 1000;
string s;
s = i; // ok, but value of `s` is not 1000!

This situation was created due to below operator from string standard library:

string& string::operator=(_CharT __c) 
{ 
  this->assign(1, __c); 
  return *this;
}

Now, this is creating an unwanted bad effect where accidentally we may end up assigning an integer to a string with erroneous value!
For example, in my case i was earlier a string and then I converted to int . The code still compiled but the program crashed due to its obvious bad effect on overall code.

This situation would be avoided, if it was:

string& operator=(const _CharT& c);

What is the motivation behind not having above version?

Answer 1

What is the motivation behind not having above version?

It doesn't solve the problem (it doesn't work how you think it works) and it would be slower.

Passing a char (or even wchar_t or char32_t ) by value is faster on most architectures than creating a reference and then accessing through the reference, because it requires passing a pointer-sized object (which is usually bigger than a char and on 64-bit systems is probably also bigger than wchar_t ) and then doing an indirection through a pointer.

So it would not fix the problem you are trying to fix it would just make code slower. Double bad.

C++ allows int to char conversion, so your suggested overload would just create that temporary then bind a reference to it. See http://open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#2372 for a better "fix", which has its own problems and is probably not going to happen.