结构体的对齐方式以及结构体嵌套指针的使用方法

　　结构体数组
　　定义结构体数组的方法很简单，同定义结构体变量是一样的，只不过将变量改成数组。或者说同前面介绍的普通数组的定义是一模一样的，如： struct STUDENT stu[10];
　　这就定义了一个结构体数组，共有 10 个元素，每个元素都是一个结构体变量，都包含所有的结构体成员。 #define _CRT_SECURE_NO_WARNINGS #include #include #include #include  typedef struct Teacher {     char name[50];     //char* name;     int age; }Teacher; int main() {     Teacher  a[3] = {          {＂a＂,11},         {＂b＂,12},         {＂c＂,13}      };     //静态     Teacher a2[3] = { ＂aa＂,13,＂bb＂,12 ,＂cc＂,13};     for (int i = 0; i < 3; i++)     {         printf(＂%s, %d ＂, a2[i].name, a2[i].age);     }     int b[3] = { 0 };     int* pB = (int*)malloc(3 * sizeof(int));     free(pB);     //Teacher p[3]     Teacher* p = (Teacher*)malloc(3 * sizeof(Teacher));     if (p==NULL)     {         return -1;     }     char buf[50];     for (int i = 0; i < 3; i++)     {         sprintf(buf, ＂name%d%d%d＂, i, i, i);         strcpy(p[i].name, buf);         p[i].age = 20 + i;     }     for (int i = 0; i < 3; i++)     {         printf(＂第%d个：%s,%d ＂, i + 1, p[i].name, p[i].age);     }     printf(＂ ＂);      if (p!=NULL)     {         free(p);         p = NULL;     }     return 0; }结构体嵌套一级指针#define _CRT_SECURE_NO_WARNINGS #include #include #include #include    typedef struct Teacher {     char* name;     int age; }Teacher;  showTeacher(Teacher* q, int n) {     for (int i = 0; i < n; i++)     {         printf(＂%s ,%d ＂, q[i].name, q[i].age);     } }  freeTeacher(Teacher* q, int n) {     for (int i = 0; i < n; i++)     {         if (q[i].name != NULL)         {             free(q[i].name);             q[i].name = NULL;         }     }      if (q != NULL)     {         free(q);         q = NULL;     } }  Teacher* getMem( int n) {      Teacher*q = (Teacher*)malloc(sizeof(Teacher));     //Teacher q[3]     char buf[30];     for (int i = 0; i < n; i++)     {         q[i].name = (char*)malloc(30);         sprintf(buf, ＂name%d%d%d＂, i, i, i);         strcpy(q[i].name, buf);          q[i].age = 20 + i;     }     return q; } Teacher* getMem2(Teacher**temp,int n) {     if (temp==NULL)     {         return -1;     }     Teacher* q = (Teacher*)malloc(sizeof(Teacher));     //Teacher q[3]     char buf[30];     for (int i = 0; i < n; i++)     {         q[i].name = (char*)malloc(30);         sprintf(buf, ＂name%d%d%d＂, i, i, i);         strcpy(q[i].name, buf);          q[i].age = 20 + i;     }     *temp = q;     return 0; } int main() {     char* name = NULL;     name = (char*)malloc(30);     strcpy(name, ＂aa＂);     printf(＂name=%s ＂, name);     if (name!=NULL)     {         free(name);         name = NULL;     }      //1     Teacher t;     t.name = (char*)malloc(30);     strcpy(t.name, ＂s＂);     t.age = 22;     printf(＂name=%s  age=%d ＂, t.name, t.age);     if (t.name!=NULL)     {         free(t.name);         t.name = NULL;     }      //2     Teacher* p = NULL;     p = (Teacher*)malloc(sizeof(Teacher));     p->name = (char*)malloc(30);     strcpy(p->name, ＂ss＂);     p->age = 22;     printf(＂name=%s  age=%d ＂, p->name, p->age);      if (p->name!=NULL)     {         free(p->name);         p->name = NULL;     }     if (p!=NULL)     {         free(p);         p = NULL;     }        //3     Teacher* q = NULL;     //q = getMem(3);     int ret = 0;     ret = getMem2(&q, 3);     if (ret!=NULL)     {         return ret;     }     showTeacher(q,3);     freeTeacher(q, 3);     p = NULL;     return 0; }结构体嵌套二级指针#define _CRT_SECURE_NO_WARNINGS #include #include #include #include  //一个导师有若干学生 typedef struct Teacher {     int age;     char**stu;//二维内存 }Teacher;  //n1老师个数  n2每个老师带的学生数 int createTeacher(Teacher** temp, int n1,int n2) {     if (temp==NULL)     {         return -1;     }     Teacher* q = (Teacher*)malloc(sizeof(Teacher) * n1);     //Teacher q[3]     for (int i = 0; i < n1; i++)     {         //q[i].stu             //(q+i)->stu         q[i].stu = (char**)malloc(sizeof(char*)*n2);         //char* stu[3]         for (int j = 0; j < n2; j++)         {             q[i].stu[j] = (char*)malloc(30);             char buf[30];             sprintf(buf, ＂name%d%d%d%d＂, i, i, j, j);             strcpy(q[i].stu[j], buf);         }         q[i].age = 20 + i;     }          *temp = q;     return 0; }  void showTeacher(Teacher* q, int n1, int n2) {     if (q=NULL)     {         return;     }      for (int i = 0; i < n1; i++)     {         printf(＂[age=%d]	＂, q[i].age);         for (int j = 0; j < n2; j++)         {             printf(＂%s,  ＂, q[i].stu[j]);         }         printf(＂ ＂);     }     printf(＂ ＂); }  void sortTeacher(Teacher*p,int n) {     if (p==NULL)     {         return;     }     Teacher temp;     for (int i = 0; i < n-1; i++)     {         for (int j = i+1; j < n; j++)         { 			if (p[i].age < p[j].age)//降序             {                 temp = p[i];                 p[i] = p[j];                 p[j] = temp;             }         }     }  }  void freeTeacher(Teacher** temp, int n1, int n2) {     if (temp==NULL)     {         return;     }     Teacher* q = *temp;     for (int i = 0; i < 3; i++)     {         for (int j = 0; j < 3; j++)         {             if (q[i].stu[j] != NULL)             {                 free(q[i].stu[j]);                 q[i].stu[j] = NULL;             }         }         if (q[i].stu != NULL)         {             free(q[i].stu);             q[i].stu = NULL;             *temp = NULL;         }     }       if (q != NULL)     {         free(q);         q = NULL;     } }  int main() {      char** name = NULL;     //char* name[3]     int n = 3;     name = (char**)malloc(sizeof(char*) * 3);     for (int i = 0; i < n; i++)     {         name[i] = (char*)malloc(30);         strcpy(name[i], ＂aaa＂);     }     for (int i = 0; i < n; i++)     {         printf(＂%s ＂, name[i]);     }      for (int i = 0; i < n; i++)     {         if (name[i]!=NULL)         {             free(name[i]);             name[i] = NULL;         }     }     if (name!=NULL)     {         free(name);         name = NULL;     }       //1     Teacher t;     //t.stu[3]      //char* t.stu[3]     int n = 3;     t.stu = (char**)malloc(sizeof(char*) * 3);     for (int i = 0; i < n; i++)     {         t.stu[i] = (char*)malloc(30);         strcpy(t.stu, ＂aaa＂);     }     for (int i = 0; i < n; i++)     {         printf(＂%s ＂,t.stu[i]);     }      for (int i = 0; i < n; i++)     {         if (t.stu[i] != NULL)         {             free(t.stu[i]);             t.stu[i] = NULL;         }     }     if (t.stu != NULL)     {         free(t.stu);         t.stu = NULL;     }       //2     Teacher* p = NULL;     //p->stu[3]     p = (Teacher*)malloc(sizeof(Teacher));      //char* t.stu[3]     int n = 3;     p->stu = (char**)malloc(sizeof(char*) * 3);     for (int i = 0; i < n; i++)     {         p->stu[i] = (char*)malloc(30);         strcpy(p->stu, ＂aaa＂);     }     for (int i = 0; i < n; i++)     {         printf(＂%s ＂, p->stu[i]);     }      for (int i = 0; i < n; i++)     {         if (p->stu[i] != NULL)         {             free(p->stu[i]);             p->stu[i] = NULL;         }     }     if (p->stu != NULL)     {         free(p->stu);         p->stu = NULL;     }      if (p!=NULL)     {         free(p);         p = NULL;     }      //3     Teacher* q = NULL;     int ret = 0;     ret = createTeacher(&q, 3,3);     //Teacher* q[3]     //q[i].stu[3]     printf(＂排序前 ＂);     showTeacher(q, 3, 3);      sortTeacher(q, 3);     printf(＂排序后 ＂);     showTeacher(q,3,3);      freeTeacher(&q, 3, 3);       return 0; } 结构体的深拷贝与浅拷贝#define _CRT_SECURE_NO_WARNINGS #include #include #include #include   typedef struct Teacher {     char* name;     int age; }Teacher;  //结构体中嵌套指针，而且动态分配空间 //同类型结构体变量赋值 //结构体成员指针变量指向同一块内存 int main() {     Teacher t1;     t1.name = (char*)malloc(30);     strcpy(t1.name, ＂tom＂);     t1.age = 22;      Teacher t2;     t2 = t1;     //深拷贝，人为增加内容，重新拷贝一下     t2.name= (char*)malloc(30);     strcpy(t2.name, t1.name);      printf(＂[t2]%s,%d ＂, t2.name, t2.age);      if (t1.name!=NULL)     {         free(t1.name);         t1.name = NULL;     }     //重复释放       //浅拷贝：t2的值还指向同一块内存 t1.name  t1释放后t2又释放 导致出现错误     if (t2.name != NULL)     {         free(t2.name);         t2.name = NULL;     }     return 0; } 结构体的对齐方式
　　结构体的对齐公式：
　　记住以下这些规则，把结构体往里面套就可以了。结构体对齐的原则就是牺牲空间的方式来减少时间的消耗，空间用完还可以复用，而时间过去了就再也不会回来了。  以 #pragma pack(x) 中 x 的大小和结构中占用空间最大的成员做比较，取小值为 n（外对齐依据）  以 n 值和结构体每个成员比较，得到结果列表为 m[x]  根据每个成员的大小依次向内存中填充数据，要求填充 成员的起始地址 减去 构体起始地址 的差都可以整除 m[x] ，如不能整除则向后移动，直到可以整除再填充成员到内存（内对齐依据）  当全部成员填充完毕后所占用的字节若不能整除 n，则扩充内存到可以整除 n 为止。
　　举个例子：
　　在这个例子中struct data的大小为8个字节。