LCppC backport: Improved CheckStl::string_c_str()

[PKEuS]

As a follow-up to the discussion in PR4143, I am starting to provide a few fixes/improvements from LCppC to cppcheck.

[pfultz2]

It seems like this check for conversion of c_str to string should use getParentValueTypes to get the type its converted to. A simpler version could be like this:

for (const Token *tok = scope.bodyStart; tok && tok != scope.bodyEnd; tok = tok->next()) {
    if (!Token::Match(tok, ". c_str|data ( )"))
        continue;
    if (!astIsContainer(tok->astOperand2()))
        continue;
    for(const ValueType& vt:getParentValueType(tok->tokAt(2), mSettings)) {
        if (!vt.container)
            continue;
        // Warn on conversion back to string
        string_c_str(tok);
        break;
    }
}

This would most likely handle a lot more cases than the current checkers do, and is much simpler.

Now all the checks for "Dangerous usage of c_str()" can probably be removed as the lifetime checker should catch all of those.

[PKEuS]

Now all the checks for "Dangerous usage of c_str()" can probably be removed as the lifetime checker should catch all of those.

Would be nice, but it does not seem to be the case.

[pfultz2]

Ah yea then we should open issues for the gaps there so we can fix the lifetime checker.