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Postfix Increment and Decrement Operators: ++ and --


The latest version of this topic can be found at Postfix Increment and Decrement Operators: ++ and --.


postfix-expression ––  

C++ provides prefix and postfix increment and decrement operators; this section describes only the postfix increment and decrement operators. (For more information, see Prefix Increment and Decrement Operators.) The difference between the two is that in the postfix notation, the operator appears after postfix-expression, whereas in the prefix notation, the operator appears before expression. The following example shows a postfix-increment operator:


The effect of applying the postfix increment operator (++) is that the operand's value is increased by one unit of the appropriate type. Similarly, the effect of applying the postfix decrement operator (––) is that the operand's value is decreased by one unit of the appropriate type.

It is important to note that a postfix increment or decrement expression evaluates to the value of the expression prior to application of the respective operator. The increment or decrement operation occurs after the operand is evaluated. This issue arises only when the postfix increment or decrement operation occurs in the context of a larger expression.

When a postfix operator is applied to a function argument, the value of the argument is not guaranteed to be incremented or decremented before it is passed to the function. See section 1.9.17 in the C++ standard for more information.

Applying the postfix increment operator to a pointer to an array of objects of type long actually adds four to the internal representation of the pointer. This behavior causes the pointer, which previously referred to the nth element of the array, to refer to the (n+1)th element.

The operands to postfix increment and postfix decrement operators must be modifiable (not const) l-values of arithmetic or pointer type. The type of the result is the same as that of the postfix-expression, but it is no longer an l-value.

The operand of a postfix increment operator may also be of type bool, in which case the operand is evaluated and then set to true. The operand of a postfix decrement operator cannot be of type bool.

The following code illustrates the postfix increment operator:

// expre_Postfix_Increment_and_Decrement_Operators.cpp  
// compile with: /EHsc  
#include <iostream>  
using namespace std;  
int main() {  
   int i = 10;  
   cout << i++ << endl;  
   cout << i << endl;  

Postincrement and postdecrement operations on enumerated types are not supported:

enum Compass { North, South, East, West );  
Compass myCompass;  
for( myCompass = North; myCompass != West; myCompass++ ) // Error  

Postfix Expressions
C++ Operators
C++ Built-in Operators, Precedence and Associativity
C Postfix Increment and Decrement Operators