What changes occur in the std::string object during copying?

When copying a std::string object, a new object is created that contains a copy of the original string. Depending on the implementation of the standard library, copying can be implemented through copying the buffer with characters (deep copy) or using optimizations such as copy-on-write (although in modern implementations, copy-on-write is usually not used due to issues with thread safety).

As a result, after copying, the new object has its own memory space for storing the string, independent of the original object. Changes in one object do not affect the other.

Example:

std::string s1 = "Hello";
std::string s2 = s1; // copying the string
s2[0] = 'h';
// s1 remains "Hello", s2 becomes "hello"