We have the question is there a performance difference between i++
and ++i
in C?
What's the answer for C++?
[Executive Summary: Use ++i
if you don't have a specific reason to use i++
.]
For C++, the answer is a bit more complicated.
If i
is a simple type (not an instance of a C++ class), then the answer given for C ("No there is no performance difference") holds, since the compiler is generating the code.
However, if i
is an instance of a C++ class, then i++
and ++i
are making calls to one of the operator++
functions. Here's a standard pair of these functions:
Foo& Foo::operator++() // called for ++i
{
this->data += 1;
return *this;
}
Foo Foo::operator++(int ignored_dummy_value) // called for i++
{
Foo tmp(*this); // variable "tmp" cannot be optimized away by the compiler
++(*this);
return tmp;
}
Since the compiler isn't generating code, but just calling an operator++
function, there is no way to optimize away the tmp
variable and its associated copy constructor. If the copy constructor is expensive, then this can have a significant performance impact.