[advanced pointer (1)] | detailed explanation of character pointer, pointer array, array pointer

All great actions and thoughts , There's a tiny beginning .

                                                                                    hello world.

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Catalog

Character pointer

Pointer array

Array pointer

Array parameters 、 Pointer parameter

Array parameters ：

One dimensional array parameters ：

Two dimensional array parameters ：

The pointer passes the parameter

First level pointer parameter transfer

The secondary pointer transmits parameters ：

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Character pointer

Character pointers are pointer variables that point to character data . We know c There are integers in language , floating-point , Character type but no string type , We usually use character arrays to store strings .

in addition ,C The language also supports using a pointer to a string to represent a string .

Be careful , When assigning values like this ,“abcdef” by Constant string ,"abcdef" It stands for Constant , It's not about putting abcdef Put it in the pointer , Is actually the First character a Address assigned to p, So let's verify that

First , Let's start with Double quotes The role of ：

1. Applied for space ( In the constant area ), Stored string  

2. Add... At the end of the string '/0'    

3. return Address

  Why can string constants be assigned to character pointer variables ？

Because it defines an ordinary character pointer , There is no defined space to store "abc", So the compiler has to help us find a place to put "abc", obviously , Take this "abc" As a constant and put it in the constant area of the program is the most appropriate choice for the compiler ."abcdef" The value of is not the character itself , It's the return address , If it is an address, you can receive it with a pointer . So you can assign string constants to character pointer variables .

Be careful , When storing strings with character arrays ,"abcdef" Not a constant string , Defining a character array defines the space for storing strings , Character array is to store characters one by one , So the compiler

will char [] = "abcdef" It can be interpreted as char[]={'a',b'','c','d','e','f','\0'};

because “abcdef” Is a constant string , therefore Its value cannot be modified , as follows , Program crash .

We'd better use const Decorate it , The program will not make mistakes

Do an exercise ~

What is the output ？

analysis ： Creating arrays requires space , Different arrays need to open up different spaces , therefore arr1 and arr2 The memory space is different , The array name is the first element address , Different space , Address different , therefore arr1 !=arr2; and “abcdef” Is a constant string , Stored in the constant area , Do not modify the , Fixed address , Is the first character a The address of , therefore p1==p2.

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Pointer array

The pointer array is Array , Is an array of addresses .

[  ] The priority ratio * high , therefore parr With the first [ ] combination , Represents an array , Array elements are Pointers .

Analogical analysis ：

The application of pointer array ：

A profound ~

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Array pointer

What is an array pointer ？ The same thing , First , It's a pointer . It's an array .

The pointer to the array is the array pointer .

Analogical analysis ：

int *p=NULL;//p It's a plastic pointer -- Pointer to the shape -- Can store plastic address 

char* pc=NULL;//p It's a character pointer -- Pointer to character -- An address where characters can be stored 

char (*p)[10];//p It's an array pointer -- Pointer to array -- The address where the array can be stored 

Application of array pointer

Here we need to pay attention to ,&arr It takes out the address of the entire array , namely p Pointer is arr The address of , namely p==&arr;&arr And array names arr Meaning is different .*p Dereference operation makes it get this array , namely *p==arr,arr For array name （ First element address ）

This is too awkward and troublesome. We don't usually use it like this , Array pointer is efficient only when it is used above two-dimensional array .

Let's take a look

There are two forms of array parameters ：

The first one is ：

The second kind ：

Let's analyze the second form of parameter transmission ：

Two dimensional array array array name first element address ; But what is the address of the first element of a two-dimensional array ？

When we say that the array name is the address of the first element , We need to Think of a two-dimensional array as a one-dimensional array , The first line is the first element , The second element in the second line , The first line is another one-dimensional array , The array has five elements , Each element is int, The address of the first element of the array name of a two-dimensional array is the address of the first line , Is the address of a one-dimensional array , So when passing parameters, we can use array pointer to receive .

Let's analyze three prints ：

Play a wave of questions ~

The last parsing ：

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Array parameters 、 Pointer parameter

When writing code, we need to put Array perhaps The pointer Pass to function , How to design the parameters of the function ？

Array parameters ：

One dimensional array parameters ：

Two dimensional array parameters ：

The pointer passes the parameter

First level pointer parameter transfer

reflection ：

When the parameter part of a function is a first-order pointer , What parameters can a function accept ？

void test1(int* p) //test1 What parameters can a function accept ？
{}
void test2(char* p)  //test1 What parameters can a function accept ？
{}

answer ：1. The pointer 2. Variable address

The secondary pointer transmits parameters ：

reflection ：

When the parameter part of a function is a secondary pointer , What parameters can a function accept ？

1. The address of the first level pointer

2. The secondary pointer

3. Pointer array