Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur télécharger pdf (Page 61)

Lvalues

An lvalue is an object locator: an expression that designates an object. An example

of an lvalue expression is *P, where P is any expression evaluating to a non-null

pointer. A modifiable lvalue is an identifier or expression that relates to an object

that can be accessed and legally changed in memory. A const pointer to a constant,

for example, is not a modifiable lvalue. A pointer to a constant can be changed

(but its dereferenced value cannot).

Historically, the l stood for “left”, meaning that an lvalue could legally stand on

the left (the receiving end) of an assignment statement. Now only modifiable lval-

ues can legally stand to the left of an assignment operator. For example, if a and b

are nonconstant integer identifiers with properly allocated memory storage, they

are both modifiable lvalues, and assignments such as

a = 1 and b = a + b are

legal.

Rvalues

The expression a + b is not an lvalue: a + b = a is illegal because the expres-

sion on the left is not related to an object. Such expressions are sometimes called

rvalues (short for right values).

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Abl-electronic PIC Microcontrollers PIC16 Manuel d'utilisateur Page 61