operator++ (also called the increment operator) increases an integer's value by one. To decrease an integer's value by one, use operator--
operator++ has a pre-fix and post-fix form, which are '++i' and 'i++' respectively. The prefix form returns the value of i its new value, the postfix form returns the value of i before its increment. Prefer '++i' over 'i++' [1,2].
#include <cassert> int main() { int i = 0; ++i; // preferred [1] assert(i==1); i++; // not preferred [1] assert(i==2); }
There are four ways to increment a value by 1, that make use of different operators and some of temporary copies.
Code Temporary copy yes/no
i = i + 1; yes
i += 1; no
++i; yes
i++; no
struct MyInt { //Prefix MyInt& operator++() { ++mX; //Increment return *this; //Return class reference } //Postfix MyInt operator++(int) { MyInt old(*this); //Copy ++(*this); //Increment original using prefix return old; //Return old copy } int mX; }; int main() { MyInt m; ++m; m++; }
- Bjarne Stroustrup. The C++ Programming Language (3rd edition). 1997. ISBN: 0-201-88954-4. Item 19.5.7: 'Prefer ++p to p++'
- Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 11.6. Advice. page 303: '[1] Prefer prefix ++ over suffix ++'