熬夜整理的C語言/C++萬字總結（四）

1、結構體

1.1 結構體基礎知識

1.1.1 結構體類型的定義

struct Person{
 char name[64];
 int age;
};
typedef struct _PERSON{
 char name[64];
 int age;
}Person;      

注意：定義結構體類型時不要直接給成員指派，結構體隻是一個類型，編譯器還沒有為其配置設定空間，隻有根據其類型定義變量時，才配置設定空間，有空間後才能指派。

1.1.2 結構體變量的定義

struct Person{
 char name[64];
 int age;
}p1; //定義類型同時定義變量
struct{
 char name[64];
 int age;
}p2; //定義類型同時定義變量
struct Person p3; //通過類型直接定義      

1.1.3 結構體變量的初始化

struct Person{
 char name[64];
 int age;
}p1 = {"john",10}; //定義類型同時初始化變量
struct{
 char name[64];
 int age;
}p2 = {"Obama",30}; //定義類型同時初始化變量
struct Person p3 = {"Edward",33}; //通過類型直接定義      

1.1.4 結構體成員的使用

struct Person{
 char name[64];
 int age;
};
void test(){
 //在棧上配置設定空間
 struct Person p1;
 strcpy(p1.name, "John");
 p1.age = 30;
 //如果是普通變量，通過點運算符操作結構體成員
 printf("Name:%s Age:%d\n", p1.name, p1.age);
 //在堆上配置設定空間
 struct Person* p2 = (struct Person*)malloc(sizeof(struct Person));
 strcpy(p2->name, "Obama");
 p2->age = 33;
 //如果是指針變量，通過->操作結構體成員
 printf("Name:%s Age:%d\n", p2->name, p2->age);
}      

1.1.5 結構體指派

1.1.5.1 指派基本概念

相同的兩個結構體變量可以互相指派，把一個結構體變量的值拷貝給另一個結構體，這兩個變量還是兩個獨立的變量。

struct Person{
 char name[64];
 int age;
};
void test(){
 //在棧上配置設定空間
 struct Person p1 = { "John" , 30};
 struct Person p2 = { "Obama", 33 };
 printf("Name:%s Age:%d\n", p1.name, p1.age);
 printf("Name:%s Age:%d\n", p2.name, p2.age);
 //将p2的值指派給p1
 p1 = p2;
 printf("Name:%s Age:%d\n", p1.name, p1.age);
 printf("Name:%s Age:%d\n", p2.name, p2.age);
}      

1.1.5.1 深拷貝和淺拷貝

//一個老師有N個學生
typedef struct _TEACHER{
 char* name;
}Teacher;
void test(){
 Teacher t1;
 t1.name = malloc(64);
 strcpy(t1.name , "John");
 Teacher t2;
 t2 = t1;
 //對手動開辟的記憶體，需要手動拷貝
 t2.name = malloc(64);
 strcpy(t2.name, t1.name);
 if (t1.name != NULL){
  free(t1.name);
  t1.name = NULL;
 }
 if (t2.name != NULL){
  free(t2.name);
  t1.name = NULL;
 }
}
1.1.6 結構體數組
struct Person{
 char name[64];
 int age;
};
void test(){
 //在棧上配置設定空間
 struct Person p1[3] = {
  { "John", 30 },
  { "Obama", 33 },
  { "Edward", 25}
 };
 struct Person p2[3] = { "John", 30, "Obama", 33, "Edward", 25 };
 for (int i = 0; i < 3;i ++){
  printf("Name:%s Age:%d\n",p1[i].name,p1[i].age);
 }
 printf("-----------------\n");
 for (int i = 0; i < 3; i++){
  printf("Name:%s Age:%d\n", p2[i].name, p2[i].age);
 }
 printf("-----------------\n");
 //在堆上配置設定結構體數組
 struct Person* p3 = (struct Person*)malloc(sizeof(struct Person) * 3);
 for (int i = 0; i < 3;i++){
  sprintf(p3[i].name, "Name_%d", i + 1);
  p3[i].age = 20 + i;
 }
 for (int i = 0; i < 3; i++){
  printf("Name:%s Age:%d\n", p3[i].name, p3[i].age);
 }
}      

1.2 結構體嵌套指針

1.2.1 結構體嵌套一級指針

struct Person{
 char* name;
 int age;
};
void allocate_memory(struct Person** person){
 if (person == NULL){
  return;
 }
 struct Person* temp = (struct Person*)malloc(sizeof(struct Person));
 if (temp == NULL){
  return;
 }
 //給name指針配置設定記憶體
 temp->name = (char*)malloc(sizeof(char)* 64);
 strcpy(temp->name, "John");
 temp->age = 100;
 *person = temp;
}
void print_person(struct Person* person){
 printf("Name:%s Age:%d\n",person->name,person->age);
}
void free_memory(struct Person** person){
 if (person == NULL){
  return;
 }
 struct Person* temp = *person;
 if (temp->name != NULL){
  free(temp->name);
  temp->name = NULL;
 }
 free(temp);
}
void test(){
 struct Person* p = NULL;
 allocate_memory(&p);
 print_person(p);
 free_memory(&p);
}      

1.2.2 結構體嵌套二級指針

//一個老師有N個學生
typedef struct _TEACHER{
 char name[64];
 char** students;
}Teacher;
 
void create_teacher(Teacher** teacher,int n,int m){
 
 if (teacher == NULL){
  return;
 }
 
 //建立老師數組
 Teacher* teachers = (Teacher*)malloc(sizeof(Teacher)* n);
 if (teachers == NULL){
  return;
 }
 
 //給每一個老師配置設定學生
 int num = 0;
 for (int i = 0; i < n; i ++){
  sprintf(teachers[i].name, "老師_%d", i + 1);
  teachers[i].students = (char**)malloc(sizeof(char*) * m);
  for (int j = 0; j < m;j++){
   teachers[i].students[j] = malloc(64);
   sprintf(teachers[i].students[j], "學生_%d", num + 1);
   num++;
  }
 }
 
 *teacher = teachers; 
}
 
void print_teacher(Teacher* teacher,int n,int m){
 for (int i = 0; i < n; i ++){
  printf("%s:\n", teacher[i].name);
  for (int j = 0; j < m;j++){
   printf("  %s",teacher[i].students[j]);
  }
  printf("\n");
 }
}
 
void free_memory(Teacher** teacher,int n,int m){
 if (teacher == NULL){
  return;
 }
 
 Teacher* temp = *teacher;
 
 for (int i = 0; i < n; i ++){
  
  for (int j = 0; j < m;j ++){
   free(temp[i].students[j]);
   temp[i].students[j] = NULL;
  }
 
  free(temp[i].students);
  temp[i].students = NULL;
 }
 
 free(temp);
 
}
 
void test(){
 
 Teacher* p = NULL;
 create_teacher(&p,2,3);
 print_teacher(p, 2, 3);
 free_memory(&p,2,3);
}