What is the structure of C language?

This article is about how C language constructs look. Xiaobian thinks it is quite practical, so share it with everyone for reference. Let's follow Xiaobian and have a look.

structure

A structure is a collection of values called member variables. Each member of a structure is a variable of a different type.

Why do we need structures?

For example, when describing a student, you need to have

name

gender

age

height

to describe them together, you need different variables, you have struct types to describe them.

declaration struct tag{ member-list//member list}variable-list;//variable list

For example, a student

struct stu{ char name[20]; char sex[5]; int age; int height;};//There is no variable list here

struct stu{ char name[20]; char sex[5]; int age; int height;}s2,s3,s4;//s2,s3,s4 global variables struct stu s5;int main(){ struct stu s1;//struct variable}

specific detailed information

When declaring structs, you can declare them incompletely

struct{ char c; int a; double a;}sa;//anonymous struct variable, variable must be defined here, otherwise cannot use int main(){ return 0;}

The compiler thinks ps and &sa are two types, which is wrong.

Data structure: The structure of data stored in memory

About the list

struct node{ int date; struct node next;};int main(){ return 0;}

So you can't tell the size of a structure, you just need to store a pointer to the next structure.

struct node{ int date; struct node* next;};int main(){ return 0;}

也可以这样（重命名使用举例）

typedef struct node{ int date; struct node* next;}node;int main(){ struct node n2 = { 0 };//2者都可以使用 node n = { 0 };//尽量不对结构体使用typedef}结构体变量的定义和初始化struct point{ int x; int y;}p1; //声明类型同时定义变量p1struct point p2;//定义结构体变量p2//初始化：定义变量的同时赋初值struct point p3 = { 1,2 };struct stu //类型声明{ char name[15];//名字 int age; //年龄};struct stu s = { "zhangsan",20 };//初始化struct node{ int date; struct point p; struct node* next;}n1 = { 10,{4,5},NULL }; //结构体嵌套初始化struct node n2 = { 20,{5,6},NULL };//结构体嵌套初始化结构体大小计算

先来观察下列代码

#include int main(){ struct S1{ char c1; int i; char c2;};printf("%d\n", sizeof(struct S1));//练习2struct S2{ char c1; char c2; int i;};printf("%d\n", sizeof(struct S2));//练习3struct S3{ double d; char c; int i;};printf("%d\n", sizeof(struct S3));//练习4-结构体嵌套问题struct S4{ char c1; struct S3 s3; double d;};printf("%d\n", sizeof(struct S4));return 0;}

发现并不是数据类型大小的简单相加

存在对齐

如何计算？

首先得掌握结构体的对齐规则：

1. 第一个成员在与结构体变量偏移量为0的地址处。

2. 其他成员变量要对齐到某个数字（对齐数）的整数倍的地址处。

对齐数 = 编译器默认的一个对齐数 与 该成员大小的较小值。

VS中默认的值为8

3. 结构体总大小为最大对齐数（每个成员变量都有一个对齐数）的整数倍。

4. 如果嵌套了结构体的情况，嵌套的结构体对齐到自己的最大对齐数的整数倍处，结构体的整

体大小就是所有最大对齐数（含嵌套结构体的对齐数）的整数倍。

为什么存在内存对齐 ?

大部分的参考资料都是如是说的：

1. 平台原因(移植原因)：

不是所有的硬件平台都能访问任意地址上的任意数据的;某些硬件平台只能在某些地址处取某些特

定类型的数据，否则抛出硬件异常。

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