How to swap two integers in C++
Warning: this post got embarrassingly long. For the short version, read up through the paragraph that starts with “If you use.”
This is something that’s been bugging me for a while, and I’d like to lay it to rest. If you’ve done any work in C++, you’ve probably heard the riddle about how to swap two integers without using a temporary variable. The question is exactly what it sounds like: you have two integers (call them x and y), you want to swap their values, and you may or may not want to use a third, temporary variable while doing it. Here are some ways of swapping integers that I have actually seen in professional code written by professional coders:
| Method Name | Code |
|---|---|
| Method A |
{ // Limit the scope of t
int t = x;
x = y;
y = t;
}
|
| Method B |
x ^= y; y ^= x; x ^= y; |
| Method C |
x ^= y ^= x ^= y; |
| Method D |
x = x + y; y = x - y; x = x - y; |
| Method E |
std::swap(x, y); |
Which of these is the fastest way to swap integers? Which way is the fastest method that doesn’t require extra memory? When will you want to use a different method? What is the overall best method?
Try to come up with some answers before reading further.
When you’ve decided on your answers, let’s take a closer look. No, on second thought, this got really long. For those of you who don’t want to read all the way to the end, let me just get my main point out of the way. After that, we’ll take a closer look. If you don’t want to spoil the ending, skip the next paragraph.
If you use this link you will spoil the ending, so skip to the next paragraph after this one. →