Releasing Memory
When you have finished with memory that has been allocated, you should never forget to free the memory as it will free up resources and improve speed. To release allocated memory, use the free function.
free(ptr);
Structures
As well as the basic data types, C has a structure mechanism that allows you to group data items that are related to each other under a common name. This is commonly referred to as a User Defined Type.
The keyword struct starts the structure definition, and a tag gives the unique name to the structure. The data types and variable names added to the structure are members of the structure. The result is a structure template that may be used as a type specifier. The following is a structure with a tag of month.
struct month
{
char name[10];
char abbrev[4];
int days;
};
A structure type is usually defined near to the start of a file using a typedef statement. typedef defines and names a new type, allowing its use throughout the program. typedef usually occur just after the #define and #include statements in a file.
The typedef keyword may be used to define a word to refer to the structure rather than specifying the struct keyword with the name of the structure. It is usual to name the typedef in capital letters. Here are the examples of structure definition.
typedef struct {
char name[64];
char course[128];
int age;
int year;
} student;
This defines a new type student variables of type student can be declared as follows.
student st_rec;
Notice how similar this is to declaring an int or float. The variable name is st_rec, it has members called name, course, age and year. Similarly,
typedef struct element
{
char data;
struct element *next;
} STACKELEMENT;
A variable of the user defined type struct element may now be declared as follows.
STACKELEMENT *stack;
Consider the following structure:
struct student
{
char *name;
int grade;
};
A pointer to struct student may be defined as follows.
struct student *hnc;
When accessing a pointer to a structure, the member pointer operator, -> is used instead of the dot operator. To add a grade to a structure,
s.grade = 50;
You could assign a grade to the structure as follows.
s->grade = 50;
As with the basic data types, if you want the changes made in a function to passed parameters to be persistent, you have to pass by reference (pass the address). The mechanism is exactly the same as the basic data types. Pass the address, and refer to the variable using pointer notation.
|
