Storage of C language data in memory (1)

stay C In language , There are many types of data . for example ：char、int、float,double wait . These are all available in C Data types created in language , Then the write data type is in memory How much storage space does it occupy ？ It's very simple, just use sizeof You can figure out how much space these data types occupy . As shown in the figure ：

If you classify data types , Can be divided into Plastic surgery Family 、 Floating point family 、 Construction type 、 Pointer type and null type .

First of all Plastic surgery Family ： Plastic surgery Family char、short、int、long.

Someone might be right char Feel confused ,char Isn't it the data type of characters , Why is it in the plastic surgery family ？ In fact, I also had this doubt at first . Now let me answer for you ：char Although it is the data type of characters , But when stored in memory , What is stored is the of characters ascii Code value ,ascii The code value is an integer . therefore char Plastic surgery Family .

Add ： Usually, the variables we create are char n1,short n2,int n3,long n4. In fact, it is an ellipsis in this way .unsigned It's a sign free signed It's signed . Look at the picture below ：

  Floating point family ：

float and double

Construction type ：

An array type 、 Type of structure （struct）、 Enumeration type (enum) And joint types (union).

Pointer types :

char *p1,int *p2,float *p3,void *p4.

Empty type ：

Namely void. Usually applied to the return type of a function 、 The parameters of the function 、 Pointer types .

Shaping storage in memory ：

Want to find out how plastic is stored in memory , You need to know the computer Original code 、 Inverse code 、 Complement code These three concepts .

There are three ways of expression Sign bit and Value bits Two parts , The sign bits are all used 0 Express “ just ”, use 1 Express “ negative ”.

A positive number 、 back 、 The complement is the same .

The three representations of negative integers are different .

Original code ： Just convert the numerical value into binary according to positive and negative numbers

Inverse code ： The sign bit of the original code remains unchanged , The other bits are reversed bit by bit

Complement code ： Inverse code +1 All you get is a complement

For plastic surgery ： Data stored in memory is actually stored in the complement .

for example ：

int a = 5   

I've done that before ,int In memory 4 Bytes , Namely 32 individual bit position .

Original code ：00000000000000000000000000000101

Inverse code ：00000000000000000000000000000101

Complement code ：00000000000000000000000000000101

A positive number 、 back 、 The complement is the same .

int b =  -5

Original code ：10000000000000000000000000000101

Inverse code ：111111111111111111111111111111111010  // The sign bits remain the same , Reverse the original code by bit

Complement code ：111111111111111111111111111111111011  // Inverse code +1

notes ： I talked about it before. char Also a member of the plastic surgery family . that char How is it stored in memory ？

It's simple .char Its size is 1 Bytes , That is to say 8 individual bit position . Convert to binary 8 digit .

The first bit is still the sign bit .

 

  If you use char Express Positive numbers It can only mean 0~127  If it means negative Can be said -1~-128. Simply speaking char It can only mean -128 To 127 Integer between .

Therefore, we can also calculate short,int and long It can represent the range of values .

summary ： You need to know how integers are stored in memory , First of all, you should know the original code of the computer 、 The concept of inverse and complement . This is especially important .