STL strings

So, while reviewing someone's code, I ran into a place where it was possible to eliminate an unnecessary string assignment. Which got me thinking - is mentioning this even worth it? How expensive is a string assignment, anyway?

So I wrote this simple program:

#define _SECURE_SCL 0

#include <string>

using namespace std;

void f(string a, string *b) {
  *b = a;
}

int main(int argc, char **argv) {
  string y = argv[0];
  string x;
  f(y, &x);
  return 0;
}

and stepped through it in the disassembler. The function f itself was inlined, so I only counted... prepare... the instructions in this call:

call        dword ptr [__imp_std::basic_string<char,std::char_traits<char>,std::allocator<char> >::operator= (402048h)] 

I skipped the call to new (argv[0] turns out to be 69 bytes, just above the default string buffer, so it does allocate), and memcpy itself (memcpy_s to be exact). The net result was - 270+ instructions. If there is no allocation, it is ~150!

This is correct - anywhere between 150 and 270 instructions of STL goo per string assignment IN ADDITION TO ACTUALLY DOING THE WORK!

I tried to do the same on Linux, and after 70-something ddd hung disassembling one of the functions...