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C language learning record 6

2022-06-11 13:39:00 【byte02】

The pointer

We know that the purpose of variable definition is to apply for space from memory to store variables , So how to find out where the variable is ？ answer ： Through the address , Memory instances also have addresses , Like we live in different places , Such as ： Bedroom address , School address ..., The same memory has addresses .

Pointer variables are variables used to store addresses .

example ：

Type identifier * Variable name (int * pa;float* pb;);

"*" Indicates that the variable is of pointer type , Type identifier (int ,float,char) Represents the type of the variable that the pointer points to

The size of the pointer variable is 4 Bytes （32 Bit platform ）/8 Bytes （64 Bit platform ）

example ：

       
       ...
       
       int 
       
       a 
       
       = 
       
       10;
       
       int
       
       * 
       
       pa 
       
       = 
       
       &
       
       a;
       
       //&a Take out a The address of variables in memory is stored in pa In this pointer variable 
       
       *
       
       pa;
       
       // adopt “*” Operators can access variables indirectly a
       
...
      
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Structure

Used to describe the type of a complex object , This type is created by the developer

example ：

       
       ...
       
       struct 
       
       stu
       
{
       
       char 
       
       name[
       
       30];
       
       int 
       
       age;
       
       char 
       
       sex[
       
       10];
       
  ...
       
};
       
       // Semicolon with table structure type ends 
       
...
      
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Use keywords as above struct Created a stu The type of

How to use this type and access its members ？

       
       ...
       
       struct 
       
       stu
       
{
       
       char 
       
       name[
       
       20];
       
       int 
       
       age;
       
       char 
       
       sex[
       
       10];
       
};
       
       int 
       
       main()
       
{
       
       struct 
       
       stu 
       
       s1
       
       ={
       
       " Zhang San "
       
       ,20,
       
       " male "}
       
       // Use structure type stu establish s1 The structural variable of 
       
       s1.
       
       name;
       
       // adopt “.” Operator to access structure member variables 
       
       return 
       
       0;
       
}
      
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Structure pointer variable and variable access

       
       ...
       
       struct 
       
       stu
       
{
       
       char 
       
       name[
       
       20];
       
       int 
       
       age;
       
       char 
       
       sex[
       
       10];
       
};
       
       int 
       
       main()
       
{
       
       struct 
       
       stu 
       
       s1
       
       ={
       
       " Zhang San "
       
       ,20,
       
       " male "}
       
       // Use structure type stu establish s1 The structural variable of 
       
       s1.
       
       name;
       
       // adopt “.” Operator to access structure member variables 
       
       struct 
       
       stu
       
       * 
       
       ps 
       
       = 
       
       &
       
       s1;
       
       // Change the structure variable s1 The address of is fetched and stored in the structure pointer variable ps in 
       
    (
       
       *
       
       ps).
       
       name;
       
       // Or through “*” Operator to introduce access , But unlike before, you need parentheses “()” Cover up . But it seems inconvenient , It's not convenient to write 
       
       ps
       
       ->
       
       name;
       
       // adopt "->" Operator to access structure variable members , This kind of writing is concise and clear 
       
       return 
       
       0;
       
}
      
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notes ：“.” And “->” difference “.” Applied to structural variables ,“->” Applied to structure pointer variables

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C language learning record 6

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