Question

I wonder if the void func(const char *str); refer to a valid str if I wrote as follow:

auto str = string("hello").c_str();
func(str);

How is it different from code below?

func(string("hello").c_str())

Answer 1

From Paragraph 12.2/3 of the C++11 Standard:

[…] Temporary objects are destroyed as the last step in evaluating the full-expression (1.9) that (lexically) contains the point where they were created. This is true even if that evaluation ends in throwing an exception. […]

This means that the temporary created within the expression that contains the call to func() will live until function call returns.

On the other hand, the lifetime of the temporary in the first code snippet will end up before func() is invoked, and str will be dangling. This will result in Undefined Behavior.