Efficiency of postincrement v.s. preincrement in C++ [duplicate]

Answer 1

One point of data from my experience.

Changing a post-increment to a pre-increment of a std::map::iterator in for loops resulted in noticeable savings in a core algorithm at my work.

In general, when icrementing an iterator that is a class, i.e. it is not a pointer, you should notice savings when using the pre-increment operator. The reason for it is that the pre-increment operator function changes the object in place while the post increment operator function usually involves creation of a temporary object.

A pre-increment operator is usually implemented as:

typename& typename::operator++()
{
   // Change state
   ...

   // Return the object
   return *this;
}

while a post-increment operator is usually implemented as:

typename typename::operator++(int)
{
   // Create a temporary object that is a copy of the current object.
   typename temp(*this):

   // Change state of the current object
   ...

   // Return the temporary object.
   return temp;
}