C (7), i75775c

C (7), i75775c

C pointer advanced

This chapter introduces:

In the previous section 5th, we made a preliminary understanding of the C language pointer. As the soul of the C language,

The C pointer is certainly not that simple. In this section, we will further learn the pointer, such as the second-level pointer,

Pointer array, memory allocation, and const modifier pointer constants! Next, please follow the steps of the author

The mysterious side of the C pointer should be further parsed!

This section describes the road map:

Function and pointer: ① the pointer is used as the parameter of the function:

② Pointer to the function:

③ Pointer function:

④ Main functions with Parameters

Ps: run the code: compile and generate the exe file, and then go to the directory where the exe is located: input: File Name one two three

Output: one two three

Pointer array:

Two questions: how to save a string? What if more than one is saved?

First question:

① Char name [20] = "~~~ "② Char * name = "~~~ "// The former defines the length and cannot be assigned directly. Obviously, the latter is more flexible.

Second question: see Figure

Level 2 pointer:

Dynamic Memory Allocation:

Sample Code:

Dynamically allocate the space of 10 integer types. If the size is greater than this value, it is dynamically allocated. Otherwise, realloc is used to re-allocate the memory.

Ps: the code is correct. vc6 always reports a running error. If an error occurs, use the C-Free or Visual studio compiler to try it!

1. <Span style = "font-family: Microsoft YaHei;" >#include <stdio. h>
2. # Include <stdlib. h>
3. # Define N 10
5. Int main ()
6. {
7. Int * p = 0;
8. Int I, num, * q = 0;
9. P = (int *) malloc (N * sizeof (int )));
10. If (p = 0)
11. {
12. Printf ("Memory Allocation Error! \ N ");
13. Exit (0 );
14. }
15. Printf ("Enter the number of elements to store: \ n ");
16. Scanf ("% d", & num );
17. If (num <= N)
18. {
19. For (I = 0; I <N; I ++)
20. Scanf ("% d", p + I );
21. }
22. Else
23. {
24. For (I = 0; I <num; I ++)
25. Q = (int *) realloc (p, (N + N) * sizeof (int ));
26. If (q = 0) exit (0 );
27. For (I = 0; I <num; I ++)
28. Scanf ("% d", q + I );
29. P = q;
30. }
31. For (I = 0; I <num; I ++)
32. Printf ("% 3d", * (p + I ));
34. Printf ("\ n ");
35. Free (p );
36. Return 0;
37. } </Span>

Use const to modify pointer Variables

We all know that using const to modify a variable of the basic data type can change the value stored in the variable from start to end.

Our program cannot be modified! However, modifying pointer variables is a little different:

For example:

Int a = 3, B = 4; const int * p = &;

If we add another code: p = & B;, an error will be reported.

If you add: a = 5; the Code does not have an error, * p = a = 5;

Analysis result:

When the const is used to modify the pointer, it indicates that the pointer is a constant pointer, and the value of the variable it points to can be modified;

However, it is wrong to modify the address pointed to by the pointer !!!

Many standard library functions in C add const before some pointer parameter types to protect parameters!

Ps: int * const p = & a; const int * const p = & a; is equivalent to the above!

Summary of this chapter:

① Functions and pointers:

1. pointer as the function parameter: The real parameter corresponding to the pointer parameter must be the variable address

2. pointer to the function: the first address of the function is called the pointer of the function. The function name can be used to locate and execute the function.

3. pointer function: the return value type is a pointer.

4. main Function with parameters: int main (int argc, char * argv []): the parameters are in sequence: the number of record parameters and the string array storing the parameter content

② Pointer Array

Comparison between two-dimensional array string storage and pointer array string Storage

③ Second-level pointer

Pointer to pointer variable

④ Dynamic memory allocation:

1. Memory Distribution chart

2. Use of four memory allocation functions provided by C: malloc (), calloc (), realloc (), and free ()

⑤ Use const to modify pointer Variables

The variable value pointing to the address that can be modified. What cannot be modified is the address pointed to by the pointer!

Reference: http://blog.csdn.net/coder_pig/article/details/37915063

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