Language Structure

C++ language and its implementation towards easy swift easy programming C++Builder.

This section briefly reviews concepts related to declarations: objects, storage classes, types, scope, visibility, duration, and linkage. A general knowledge of these is essential before tackling the full declaration syntax. Scope, visibility, duration, and linkage determine those portions of a program that can make legal references to an identifier in order to access its object

An object is a specific region of memory that can hold a fixed or variable value (or set of values). (This use of the word object is different from the more general term used in object-oriented languages.) Each value has an associated name and type (also known as a data type). The name is used to access the object. This name can be a simple identifier, or it can be a complex expression that uniquely references the object.
The type is used

to determine the correct memory allocation required initially.
to interpret the bit patterns found in the object during subsequent accesses.
in many type-checking situations, to ensure that illegal assignments are trapped.

C++Builder supports many standard (predefined) and user-defined data types, including signed and unsigned integers in various sizes, floating-point numbers in various precisions, structures, unions, arrays, and classes. In addition, pointers to most of these objects can be established and manipulated in memory.

The C++Builder standard libraries and your own program and header files must provide unambiguous identifiers (or expressions derived from them) and types so that C++Builder can consistently access, interpret, and (possibly) change the bit patterns in memory corresponding to each active object in your program.

Objects and declarations:

Declarations establish the necessary mapping between identifiers and objects. Each declaration associates an identifier with a data type. Most declarations, known as defining declarations, also establish the creation (where and when) of the object; that is, the allocation of physical memory and its possible initialization. Other declarations, known as referencing declarations, simply make their identifiers and types known to the compiler. There can be many referencing declarations for the same identifier, especially in a multifile program, but only one defining declaration for that identifier is allowed.

Generally speaking, an identifier cannot be legally used in a program before its declaration point in the source code. Legal exceptions to this rule (known as forward references) are labels, calls to undeclared functions, and class, struct, or union tags. rvalues

The expression a + b is not an lvalue: a + b = a is illegal because the expression on the left is not related to an object. Such expressions are often called rvalues (short for right values).


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).

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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 lvalues can legally stand to the left of an assignment statement. 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.
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