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• C++ What Is A Struct

It's a holdover from C, in which it makes a difference. The C language standard ( C89 §3.1.2.3, C99 §6.2.3, and C11 §6.2.3) mandates separate namespaces for different categories of identifiers, including tag identifiers (for struct / union / enum) and ordinary identifiers (for typedef and other identifiers). In C, all struct/union/enum/class declarations act like they are implicitly typedef'ed, as long as the name is not hidden by another declaration with the same name. See Michael Burr's. To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member. The struct statement defines a new data type, with more than one member.

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Arrays allow to define type of variables that can hold several data items of the same kind. Similarly structure is another user defined data type available in C that allows to combine data items of different kinds.

Structures are used to represent a record. Suppose you want to keep track of your books in a library. You might want to track the following attributes about each book −

• Title
• Author
• Subject
• Book ID

Defining a Structure

To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member. The format of the struct statement is as follows −

The structure tag is optional and each member definition is a normal variable definition, such as int i; or float f; or any other valid variable definition. At the end of the structure's definition, before the final semicolon, you can specify one or more structure variables but it is optional. Here is the way you would declare the Book structure −

Accessing Structure Members

To access any member of a structure, we use the member access operator (.). The member access operator is coded as a period between the structure variable name and the structure member that we wish to access. You would use the keyword struct to define variables of structure type. The following example shows how to use a structure in a program −

When the above code is compiled and executed, it produces the following result −

Structures as Function Arguments

You can pass a structure as a function argument in the same way as you pass any other variable or pointer.

When the above code is compiled and executed, it produces the following result −

Pointers to Structures

You can define pointers to structures in the same way as you define pointer to any other variable −

Now, you can store the address of a structure variable in the above defined pointer variable. To find the address of a structure variable, place the '&'; operator before the structure's name as follows −

To access the members of a structure using a pointer to that structure, you must use the → operator as follows −

C++ Struct New

Let us re-write the above example using structure pointer.

When the above code is compiled and executed, it produces the following result −

Bit Fields

Bit Fields allow the packing of data in a structure. This is especially useful when memory or data storage is at a premium. Typical examples include −

• Packing several objects into a machine word. e.g. 1 bit flags can be compacted.

• Reading external file formats -- non-standard file formats could be read in, e.g., 9-bit integers.

C allows us to do this in a structure definition by putting :bit length after the variable. Edison vst crack. For example −

Here, the packed_struct contains 6 members: Four 1 bit flags f1.f3, a 4-bit type and a 9-bit my_int.

C automatically packs the above bit fields as compactly as possible, provided that the maximum length of the field is less than or equal to the integer word length of the computer. If this is not the case, then some compilers may allow memory overlap for the fields while others would store the next field in the next word.

Data structures

A data structure is a group of data elements grouped together under one name. These data elements, known as members, can have different types and different lengths. Data structures can be declared in C++ using the following syntax:
struct type_name {
member_type1 member_name1;
member_type2 member_name2;
member_type3 member_name3;
.
.
} object_names;

Where type_name is a name for the structure type, object_name can be a set of valid identifiers for objects that have the type of this structure. Within braces {}, there is a list with the data members, each one is specified with a type and a valid identifier as its name.
For example:
This declares a structure type, called product, and defines it having two members: weight and price, each of a different fundamental type. This declaration creates a new type (product), which is then used to declare three objects (variables) of this type: apple, banana, and melon. Note how once product is declared, it is used just like any other type.
Right at the end of the struct definition, and before the ending semicolon (;), the optional field object_names can be used to directly declare objects of the structure type. For example, the structure objects apple, banana, and melon can be declared at the moment the data structure type is defined:

In this case, where object_names are specified, the type name (product) becomes optional: struct requires either a type_name or at least one name in object_names, but not necessarily both.
It is important to clearly differentiate between what is the structure type name (product), and what is an object of this type (apple, banana, and melon). Many objects (such as apple, banana, and melon) can be declared from a single structure type (product).
Once the three objects of a determined structure type are declared (apple, banana, and melon) its members can be accessed directly. The syntax for that is simply to insert a dot (.) between the object name and the member name. For example, we could operate with any of these elements as if they were standard variables of their respective types:
Each one of these has the data type corresponding to the member they refer to: apple.weight, banana.weight, and melon.weight are of type int, while apple.price, banana.price, and melon.price are of type double.
Here is a real example with structure types in action:

The example shows how the members of an object act just as regular variables. For example, the member yours.year is a valid variable of type int, and mine.title is a valid variable of type string.
But the objects mine and yours are also variables with a type (of type movies_t). For example, both have been passed to function printmovie just as if they were simple variables. Therefore, one of the features of data structures is the ability to refer to both their members individually or to the entire structure as a whole. In both cases using the same identifier: the name of the structure.
Because structures are types, they can also be used as the type of arrays to construct tables or databases of them:

Pointers to structures

Like any other type, structures can be pointed to by its own type of pointers:

Here amovie is an object of structure type movies_t, and pmovie is a pointer to point to objects of structure type movies_t

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. Therefore, the following code would also be valid:
The value of the pointer pmovie would be assigned the address of object amovie.
Now, let's see another example that mixes pointers and structures, and will serve to introduce a new operator: the arrow operator (->

C++ What Is A Struct

):

The arrow operator (->) is a dereference operator that is used exclusively with pointers to objects that have members. This operator serves to access the member of an object directly from its address. For example, in the example above:
is, for all purposes, equivalent to:

Both expressions, pmovie->title and (*pmovie).title are valid, and both access the member title of the data structure pointed by a pointer called pmovie. It is definitely something different than:
which is rather equivalent to:

This would access the value pointed by a hypothetical pointer member called title of the structure object pmovie (which is not the case, since title is not a pointer type). The following panel summarizes possible combinations of the operators for pointers and for structure members:

Expression	What is evaluated	Equivalent
a.b	Member b of object a
a->b	Member b of object pointed to by a	(*a).b
*a.b	Value pointed to by member b of object a	*(a.b)

Nesting structures

Structures can also be nested in such a way that an element of a structure is itself another structure:
After the previous declarations, all of the following expressions would be valid:

(where, by the way, the last two expressions refer to the same member).

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