【C语言】结构体详解

【C语言】结构体详解

文章目录

• 【C语言】结构体详解
• 前言
• 一、结构体的基本使用
• 二、结构体的深浅拷贝
• 三、结构体嵌套一级指针
• 四、结构体嵌套二级指针
• 五、结构体的偏移量
• 六、内存对齐
• 总结

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  前言

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  本篇文章会讲到结构体的基本使用，结构体的深浅拷贝，结构体嵌套一级指针练习，结构体嵌套二级指针练习，结构体偏移量，内存对齐的有关知识。

  一、结构体的基本使用

  代码中讲述了如何定义结构体，以及哟个typedef给结构体起别名，如何创建结构体，在堆区和栈上的不同创建形式，以及在栈上和堆区里分配内存。

  #define  _CRT_SECURE_NO_WARNINGS 1#include #include #include //用typedef起别名//struct Person//{//char name[64];//int age;//};//typedef struct Person myPersontypedef struct Person{char name[64];int age;}myPerson;void test01(){struct Person p = { "Tom",18 };myPerson p2 = { "Jerry",20 };}struct Person2{char name[64];int age;}myPerson2 = { "aaa",20 };void test02(){printf("姓名：%s 年龄：%d", myPerson2.name, myPerson2.age);  }//匿名结构体struct{char name[64];int age;}myPerson3 = { "bbb",13 };void test03(){printf("姓名：%s 年龄：%d", myPerson3.name, myPerson3.age);}//结构体的创建void test04(){//创建在栈上struct Person p = { "aaa",10 };printf("姓名：%s 年龄：%d", p.name, p.age);//创建在堆区struct Person* p2 = malloc(sizeof(struct Person));strcpy(p2->name, "bbb");p2->age = 18;printf("姓名：%s 年龄：%d", p2->name, p2->age);if (p2!= NULL){free(p2);p2 = NULL;}}void printArray(struct Person personArray[],int len){for (int i = 0; i  
  二、结构体的深浅拷贝
   
  #define  _CRT_SECURE_NO_WARNINGS 1#include#include#includestruct Person{char name[64];int age;};void test1(){struct Person p1 = { "Tom",18 };struct Person p2 = { "Jerry",20 };p1 = p2;//浅拷贝，按字节拷贝printf("p1的姓名： %s 年龄：%d\n", p1.name, p1.age);printf("p2的姓名： %s 年龄: %d\n", p2.name, p2.age);}struct Person2{char* name;int age;};void test2(){struct Person2 p1;p1.name = malloc(sizeof(char) * 64);strcpy(p1.name, "Tom");p1.age = 18;struct Person2 p2;p2.name = malloc(sizeof(char) * 128);strcpy(p2.name, "Jerry");p2.age = 20;//p1=p2;   //系统提供的复制操作是简单的浅拷贝，我们需要做手动复制，提供深拷贝/手动赋值///先释放原来的堆区内容if (p1.name != NULL){free(p1.name);p1.name = NULL;}//在堆区创建内存p1.name = malloc(strlen(p2.name) + 1);strcpy(p1.name, p2.name);p1.age = p2.age;/printf("p1的姓名：%s 年龄：%d\n", p1.name, p1.age);printf("p2的姓名：%s 年龄：%d\n", p2.name, p2.age);if (p1.name != NULL){free(p1.name);p1.name = NULL;}if (p2.name != NULL){free(p2.name);p2.name = NULL;}}int main(){test1();test2();return 0;}
   
  三、结构体嵌套一级指针
   
  #define  _CRT_SECURE_NO_WARNINGS 1#include#include#includestruct Person{char* name;int age;};struct Person** allocateSpace(){struct Person** temp = malloc(sizeof(struct Person*) * 3);for (int i = 0; i name = malloc(sizeof(char) * 64);//给姓名赋值sprintf(temp[i]->name, "name_%d", i + 1);temp[i]->age = 18 + i;}return temp;}void printPerson(struct Person** pArray, int len){for (int i = 0; i name, pArray[i]->age);}}void freeSpace(struct Person** pArray, int len){if (pArray == NULL){return;}if (len return;}for (int i = 0; i name);free(pArray[i]->name);pArray[i]->name = NULL;}free(pArray[i]);pArray[i] = NULL;}}void test07(){struct Person** pArray = NULL;pArray = allocateSpace();//打印数组printPerson(pArray, 3);//释放内存freeSpace(pArray,3);pArray = NULL;}int main() {test07();system("pause");return EXIT_SUCCESS;}
   
  四、结构体嵌套二级指针
   
  #define  _CRT_SECURE_NO_WARNINGS 1#include#include#includestruct Teacher{char* name;char** students;};void allocateSpace02(struct Teacher*** teachers){if (teachers == NULL){return;}//开辟内存struct Teacher**ts=malloc(sizeof(struct Teacher*) * 3);//给每个老师分配内存for (int i = 0; i name = malloc(sizeof(char) * 64);//给老师起名字sprintf(ts[i]->name, "Teacher_ % d", i + 1);//给学生的数组分配内存ts[i]->students = malloc(sizeof(char*)*4);//给学生的姓名开辟内存 以及赋值for (int j = 0; j students[j] = malloc(sizeof(char) * 64);sprintf(ts[i]->students[j], "%s_Student_%d", ts[i]->name, j + 1);}}*teachers = ts;}void printTeachers(struct Teacher** pArray){if (pArray == NULL){return;}for (int i = 0; i name);for (int j = 0; j students[j]);}}}void freeSpace02(struct Teacher** pArray){if (pArray == NULL){return;}for (int i = 0; i name != NULL){free(pArray[i]->name);pArray[i]->name = NULL;}//释放学生姓名for (int j = 0; j students[j] != NULL){free(pArray[i]->students[j]);pArray[i]->students[j] = NULL;}}//释放学生数组if (pArray[i]->students != NULL){free(pArray[i]->students);pArray[i]->students = NULL;}//释放老师if (pArray[i] != NULL){free(pArray[i]);pArray[i] = NULL;}}//释放老师数组if (pArray != NULL){free(pArray);pArray = NULL;}}void test08(){struct Teacher** pArray = NULL;//开辟内存allocateSpace02(&pArray);//打印数组printTeachers(pArray);//释放数组freeSpace02(pArray);pArray = NULL;}int main(){test08();return 0;}
   
  五、结构体的偏移量
     
  #include 
  offsetof(struct Teacher, b)
    
  #define  _CRT_SECURE_NO_WARNINGS 1#include#include#include#include struct Teacher{char a; //0 ~ 3int b;  //4 ~ 7};void test01(){struct Teacher t1;struct Teacher* p = &t1;printf("b的属性偏移量为：%d\n", (int)&(p->b) - (int)p);printf("b的属性偏移量为：%d\n", offsetof(struct Teacher, b));}//通过偏移量 操作内存void test02(){struct Teacher t1 = { 'a', 10 };printf("t1.b = %d\n", *(int*)((char*)&t1 + offsetof(struct Teacher, b)));printf("t1.b = %d\n", *(int*)((int*)&t1 + 1));}struct Teacher2{char a;int b;struct Teacher c;};void test03(){struct Teacher2 t1 = { 'a', 10, 'b', 20 };int offset1 = offsetof(struct Teacher2, c);int offset2 = offsetof(struct Teacher, b);printf("%d\n", *(int*)((char*)&t1 + offset1 + offset2));printf("%d\n", ((struct Teacher*)((char*)&t1 + offset1))->b);}int main() {//test01();//test02();test03();system("pause");return EXIT_SUCCESS;}
   
  六、内存对齐
     
  #pragma pack(show) //查看当前对齐模数 ，对齐模数是可以改的，改成2的N次方
  内存对齐要求：
  第一个属性开始 从0开始偏移
  第二个属性开始 要放在 该类型的大小 与 对齐模数比 取小的值 的整数倍
  所有属性都计算完后，再整体做二次偏移，将整体计算的结果 要放在 结构体最大类型 与对齐模数比 取小的值的 整数倍上
    
  #define  _CRT_SECURE_NO_WARNINGS 1#include#include#include#pragma pack(show) //查看当前对齐模数 ，对齐模数是可以改的，改成2的N次方typedef struct _STUDENT {int a;    //0 ~ 3      char b;   //4 ~ 7      double c; //8 ~ 15     float d;  //16 ~ 19    }Student;void test09(){printf("sizeof  student  = %zd\n", sizeof(Student));//24}//结构体嵌套结构体时候，子结构体放在该结构体中最大类型 和对齐模数比 的整数倍上即可typedef struct _STUDENT2 {char a;  // 0 ~ 7Student b; // 8  ~ 31double c;  //32 ~ 39}Student2;void test10(){printf("sizeof  student  = %d\n", sizeof(Student2));}int main() {test09();test10();system("pause");return EXIT_SUCCESS;}
   
  总结
   
  到这里这篇文章的内容就结束了，谢谢大家的观看，如果有好的建议可以留言喔，谢谢大家啦！