passing string around question

I have a member function like

setResult(const std::string &s)
{
         this->m_result =开发者_开发知识库 s;
}

After checking, I found this->m_result's address is the same as s. Will m_result disappear (or become garbage) when s goes out of scope if s is a stack object?

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Probably not; if m_result is a std::string, it will deep-copy the data contents.

Anyway, in places like assignment operators, you'd normally check against this kind of self-assignment. The idiom is:

obj& operator=(const obj& o) {
    if ( this != &o ) // ...
}

The same goes for your case, where you could potentially check it &m_result is different from the passed in string. But std::string are usually implemented so that self-copying is OK.

---

Effectively s is no stack object, as it's a reference (the reference itself is a stack object, but the string is not). Actually this->m_result can only have the same address as s, if you passed this->m_result to testResult, but although self-assignment is quite useless, in this case it doesn't do any harm.

EDIT: Another case could be, that this->m_result is not a std::string but a reference to it. Then you got a problem as you got a reference to a destroyed object. Remember, a reference is nothing more than a pointer (just more comfortable to use and with reduced functionalty).