Question

Someone want to explain me which code is faster ? and what is the best way to optimise a string assignment ?

code 1 :

std::string result;

int main()
{
   for(int i=0;i<1000;i++)
   {
   /*some code*/
   result = stringVar;
   /* some code using result */
   }
}

code 2 :

int main()
{
   for(int i=0;i<1000;i++)
   {
   /*some code*/
   std::string result = stringVar;
   /* some code using result */
   }
}

And to assigne value :

std::string var;

var.assign("value");
//or
var="value";

And it’s possible to release memory used by the value before to add a new one ?

Thank if you can help me to understand that 🙂

Answer 1

In the case of:

for (...)
    std::string result = blah;

the compiler must construct and destruct result each time through the for loop, probably requiring heap allocation and deallocation calls.

In the case of:

std::string result;
for (...)
    result = blah;

the string implementation might be able to optimize some heap allocation and deallocation away by only reallocation when blah is to big to fit in result’s current buffer.

var=x and var.assign(x) should result in the same code; I would not expect a substantial difference either way.