std::string copy constructor NOT deep in GCC 4.1.2?

Question

I wonder if i misunderstood something: does a copy constructor from std::string not copy its content?

string str1 = \"Hello World\"         


        

Answer 1

It is entirely possible that your string implementation uses copy-on-write which would explain the behavior. Although this is less likely with newer implementations (and non-conforming on C++11 implementations).

The standard places no restriction on the value of the pointer returned by c_str (besides that it points to a null-terminated c-string), so your code is inherently non-portable.

Answer 2

std::string implementation in your compiler must be reference counted. Change one of the strings and then check the pointers again - they would be different.

string str1 = "Hello World";
string str2(str1);

if(str1.c_str() == str2.c_str()) // Same pointers!
  printf ("You will get into the IPC hell very soon!!");

str2.replace(' ',',');

// Check again here.

These are 3 excellent articles on reference counted strings.

http://www.gotw.ca/gotw/043.htm

http://www.gotw.ca/gotw/044.htm

http://www.gotw.ca/gotw/045.htm