L-Value and R-Value ExpressionsExpressions that refer to memory locations are called "l-value" expressions. An l-value represents a storage region's "locator" value, or a "left" value, implying that it can appear on the left Of the equal sigh (=). L-VALUES ARE OFTENTENTIFIERS. The expression of addresses in memory is called a left value expression. A left value expression represents a "positioning" value of a storage area, or called a "left" value means it can appear on the left side of the equal sign (=), the left value is generally some flag. Expressions referring to modifiable locations are called "modifiable l-values." A modifiable l-value can not have an array type, an incomplete type, or a type with the const attribute. For structures and unions to be modifiable l-values, they must NOT HAVE ANY MEMBERS WITH The Name of the Identifier Denotes A Storage Location, While The Value Of The Variable Is The Value Stored At That Location. Some expressions are some (in memory) variable addresses A variable left value called "variable left value" cannot contain an array type, or an incomplete type, or any member with const attributes. The name of the flag means that the store is stored, and the value of this variable is stored on this address. An identifier is a modifiable l-value if it refers to a memory location and if its type is arithmetic, structure, union, or pointer. For example, if ptr is a pointer to a storage region, then * ptr is a modifiable l- Value That Designates The Storage Region to Which Ptr Points. Regardless of an arithmetic type, structure, a firing, a pointer, as long as it involves memory allocation, it is a variable left value. For example, if PTR is a pointer to a memory area, * PTR is a variable left value, which points out the area pointed to by PTR. Any of the Following C Expressions Can Be L-Value Expressions: Any expression of any CAN can be a left value expression
An Identifier of Integral, Floating, Pointer, Structure, Or Union Type represents integer, floating point, pointer, structural or a combination type
A subscript ([]) Expression That Does Not Evaluate to an Array does not mean the subscript operator of the array
A member-selection expression expression (-> or.) Member selectif (-> or.)
A unary-indirection (*) Expression That Does Not Refer to an array does not mean the array of pointer operators an L-Value Expression in ParentheSes in parentheses
A const object (a nonmodifiable l-value) The Term "R-Value" IS Sometimes Used to describe the value of an expression and to distinguish it from an l-value. All L-VALUES ARE R-VALUES But Not All r- VALUES Are L-VALUES. A constant object (a constant left value), "right value" This term is often used to describe the value of the expression and the difference and the left value, all the left values are right, But it is not established
Microsoft Specific ->
Microsoft C includes an extension to the ANSI C standard that allows casts of l-values to be used as l-values, as long as the size of the object is not lengthened through the cast. (See Type-Cast Conversions for more information. The Following Example Illustrates this feature: Microsoft C extensions the standard C, which allows the left value to the left value, as long as the length of this object does not exceed this conversion (more, see type transformation), this feature . Char * p; long L;
(long *) p = & l; / * legal cast * / (long) i = L; / * illegal cast * /
The Default for Microsoft C Is That The Microsoft Extensions Are Enabled. Use The / ZA Compiler Option To Disable The / ZA Compiler Option To Disable The / ZA Compiler Option To Disable There Extensions. Microsoft C Default This extension, you can use the / zA option to close it when compile
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