What is a structure?
A structure is a key word that create user defined data type in C/C++. A structure creates a data type that can be used to group items of possibly different types into a single type.
How to create a structure?
‘struct’ keyword is used to create a structure. Following is an example.
struct address
{
char name[50];
char street[100];
char city[50];
char state[20];
int pin;
};
How to declare structure variables?
A structure variable can either be declared with structure declaration or as a separate declaration like basic types.
// A variable declaration with structure declaration.
struct Point
{
int x, y;
} p1; // The variable p1 is declared with 'Point'
// A variable declaration like basic data types
struct Point
{
int x, y;
};
int main()
{
struct Point p1; // The variable p1 is declared like a normal variable
}Note: In C++, the struct keyword is optional before in declaration of a variable. In C, it is mandatory.
How to initialize structure members?
Structure members cannot be initialized with declaration. For example the following C program fails in compilation.
struct Point
{
int x = 0; // COMPILER ERROR: cannot initialize members here
int y = 0; // COMPILER ERROR: cannot initialize members here
};
The reason for above error is simple, when a datatype is declared, no memory is allocated for it. Memory is allocated only when variables are created.
Structure members can be initialized using curly braces ‘{}’. For example, following is a valid initialization.
struct Point
{
int x, y;
};
int main()
{
// A valid initialization. member x gets value 0 and y
// gets value 1. The order of declaration is followed.
struct Point p1 = {0, 1};
}
