Usage of pointers in C language [1]

 

Pointer is an important concept in C language and also an important feature of C language. Using pointers can make the program more concise.

1. storage of data in the memory: allocate a certain number of storage units (bytes) to the Data Type in the memory ).

2. Address of the memory unit: the number of the memory unit, which corresponds to the variable name.

3. memory unit content: Value

4. Direct Access to variables: the way to access variable values by the variable address (that is, the variable name.

5. indirect access to variables: place the variable address in another memory unit, first obtain the variable address in another memory unit, and then find the variable address for data access.

The variable pointer is a pointer variable that stores the memory address of variable I. We can say that pointer Points to the address of I.

6. pointer concept: the address of a variable is called the pointer of the variable.

7. pointer variables: variables used to store other variable addresses.

The difference between a pointer and a pointer variable, that is, the difference between a value and a variable.

Pointer variable definition:

1. Definition method: type identifier * pointer variable name;

2. Three elements of pointer variables:

Pointer variable type: consistent with the type of the Variable

Pointer variable value: address of another variable in memory

Pointer name: Starting from normal variables

3. Description

* Before the identifier indicates that the variable is a pointer variable, but * is the name of the pointer variable.

 

Pointer variable assignment: 1. pointer variable name = an address; (& get an address character)

2. pointer variable name = another assigned pointer variable

Example: int I, * p, * q;

P = & I; // method 1

Q = p; // method 2

Pointer operation

 

Example: int * p, I;

Char * q, c;

P = & I; q = & c;

P ++, q ++;

 

P ++, q ++; // after execution is complete

 

Because the int type pointed to by p occupies two bytes of space (generally) and points to 1002 after auto-increment, while the char type occupies one byte, q points to 2001

 

 

Comparison: p> q // false (use the above Program)

 

Int a [10];

Int * p, * q;

P = & a [0]; // or p =;

Q = & a [9]; // or p = a + 9;

P <q, p> q is true or false?

The figure shows that p <q is true.

 

 

Summary: Two operators:

*: Find the content in the memory address.

&: Find the memory address of the Variable

Summary of the following small program

Main ()

{

Int a, B;

Int * pointer_1, * pointer_2;

A = 100;

B = 10;

Pointer_1 = &;

Pointer_2 = & B;

Printf ("% d, % d \ n", a, B );

Printf ("% d, % d", * pointer_1, * pointer_2 );

 

}

The running result is, 10

100,10

Graphically: (p1 and p2 represent pointer_1 and pointer_2 respectively)

The following are several changes:

 

1. After executing the statement p2 = & * pointer_1, it becomes the form. In this case, * pointer_1 is a, * p2 is a, p1 = p2 = &

2. What is the meaning of "& * pointer_1?

 

3. What is the equivalent of (* pointer_1) ++?

4. * What does & a mean?