C language advanced pointer Full Version (array pointer, pointer array discrimination, function pointer)

Important concepts of pointer ：
A pointer is a variable , It's used to store the address , The address uniquely identifies a piece of memory space .
The size of the pointer is fixed 4/8 Bytes （32 Bit platform /64 Bit platform ）.
Pointers are typed , The type of pointer determines the type of pointer +- Integer step size , The permission of pointer dereference operation .
The operation of the pointer .

1. Character pointer

 

Code char* pstr = "hello bit."; It's very easy for students to think it's a string hello bit Put it in the character pointer pstr in
了 , however / The essence is to put the string hello bit. The address of the first character is put in pstr in . 

2. Pointer array  

  Take a look at the application of several pointer arrays ：

 

 3. Array pointer

Array pointers are pointers

 

  There are two exceptions when the array name is the first element address ：

 

 

  If the address passed by the parameter is ：

The use of array pointers ： 

   // Array name arr, Represents the address of the first element
  // But the first element of a two-dimensional array is the first row of a two-dimensional array
  // So the message here is arr, It's actually equivalent to the address on the first line , Is the address of a one-dimensional array
  // You can use an array pointer to receive

Let's take a look at the meaning of the following code ：

4. Array parameters 、 Pointer parameter

4.1 One dimensional array parameters

4.2 Two dimensional array parameters  

4.3 First level pointer parameter transfer  

4.4 The secondary pointer transmits parameters  

5. A function pointer  

  The output is two addresses , These two addresses are test Address of function .
The address of our function should be saved , How to keep ？

Call an instance of a function through a function pointer ：

Read two interesting pieces of code ： 

6. Function pointer array ‘

Let's start with a piece of code ：

How to simplify ？ Make it into the form of function pointer array

  Using examples ：

Design a counter ：

1. General method ：

2. adopt Function pointer array improvement A simple way ：

 

 7. A pointer to an array of function pointers

The pointer to the array of function pointers is a The pointer
The pointer points to a Array , The elements of the array are A function pointer

8. Callback function

A callback function is a function called through a function pointer . If you put a pointer to a function （ Address ） Pass as a parameter to another
A function , When this pointer is used to call the function it points to , Let's just say this is a callback function . The callback function is not created by the
The implementer of the function calls , It's called by another party when a particular event or condition occurs , For the event or
Condition response .

First demonstrate qsort Use of functions ：

So let's see first void* base The role of

size_t num It represents the number of elements to be sorted  

size_t width Represents the size of an element , Unit is byte

notes ：size_t Represents an unsigned integer

 

  Next we use qsort Function to write a bubble sort by yourself :

  notes ：Swap Notice in the function width Can't ignore , Also note that after each byte is compared, one byte must be skipped backward

Also note that this function uses the idea of callback function

9. Pointer and array written test question analysis

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The meaning of array names ：
1. sizeof( Array name ), The array name here represents the entire array , It calculates the size of the entire array .
2. & Array name , The array name here represents the entire array , It takes out the address of the entire array .
3. In addition, all array names represent the address of the first element .

4.strlen What I want is an address , Count backwards from the address passed by the parameter , until \0 Location ,\0 As many characters as there are before  

5. The array name of a two-dimensional array represents the address of the first element , But the address of the first element here refers to the address of the first line ;a[0] In a two-dimensional array, the array name in the first row

Example ：

int a[3][4];

The array name of the two-dimensional array is a;   a- The address of the first element of a two-dimensional array （ first line ） The address of

The array name in the first row is a[0];     a[0] Represents the address of the first element in the first line

The array name in the second line is a[1];     a[1] Represents the address of the first element in the second line

The array name in the third line is a[2];     a[2] Represents the address of the first element in the third line

sizeof(a)         &a

sizeof(a[0])    &a[0]

sizeof(a[1])    &a[1]

sizeof(a[2])    &a[2]    The array names of the above four cases all represent the whole array

10. Pointer written test questions

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Analysis results ： It's important to be careful here +1 What on earth is it +1, Pay attention to the conversion of types after forced type conversion

 

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a[0] Is the array name in the first row , A separate a[0] Represents the address of the first element

 

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there char** How to understand ?

char* *pa;

In front of a char* Express ++ Will skip a char* type ,*pa Express pa It's a pointer

 

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