Postfix Increment and Decrement Operators

Description

You can only apply postfix increment ++ and postfix decrement -- operators to an operand that is a modifiable lvalue with scalar type. The result of a postfix increment or a postfix decrement operation is not an lvalue.

The postfix-expression is incremented or decremented after its value is used. The expression evaluates to the value of the object before the increment or decrement, not the object's new value.

If the value of X is 2, after the expression A=X++ is evaluated, A is 2 and X is 3.

Avoid using postfix operators on a single operand appearing more than once in an expression. The result of the following example is unpredictable:

  *p++ = *p++;

The C language does not define which expression is evaluated first. The compiler can choose to evaluate the left side of the = operator (saving the destination address) before evaluating the right side. The result depends on the order of the subexpression evaluation.

Pointers are assumed to point into arrays. Incrementing (or decrementing) a pointer causes the pointer to point to the next (or previous) element. This means, for example, that incrementing a pointer to a structure causes the pointer to point to the next structure, not the next byte within the structure. (Also refer to “Additive Operators ” for information on adding to pointers.)