单例模式

一、单例模式

1.概述

构造函数为private
定义私有类型的成员变量

通过共有的静态方法实例化该成员变量

简单代码如下

#include <stdio.h>

typedef struct {
   int value;
} Singleton;

Singleton* getInstance() {
   static Singleton instance = {0};
   return &instance;
}

int main() {
   Singleton* singleton1 = getInstance();
   singleton1->value = 5;
   printf("singleton1 value: %d\n", singleton1->value); // 输出: "singleton1 value: 5"

   Singleton* singleton2 = getInstance();
   printf("singleton2 value: %d\n", singleton2->value); // 输出: "singleton2 value: 5"
   return 0;
}

2.结构图

单例模式

3.饿汉式单例类

#include <stdio.h>

typedef struct {
    int value;
} Singleton;

Singleton* getInstance() {
    static Singleton instance = {0};
    return &instance;
}

int main() {
    Singleton* singleton1 = getInstance();
    singleton1->value = 5;
    printf("singleton1 value: %d\n", singleton1->value); // 输出: "singleton1 value: 5"

    Singleton* singleton2 = getInstance();
    printf("singleton2 value: %d\n", singleton2->value); // 输出: "singleton2 value: 5"
    return 0;
}

其结构图如下

饿汉单例模式

4.懒汉单例模式

懒汉式单例在第一次调用getInstance()方法时实例化，在类加载时并不自行实例化，这种技术又称为延迟加载(Lazy Load)技术，即需要的时候再加载实例，为了避免多个线程同时调用getInstance()方法

#include <stdio.h>

typedef struct {
    int value;
} Singleton;

Singleton* getInstance() {
    static Singleton *instance;
    if(instance == NULL)
    {
        instance = (Singleton *)malloc(sizeof(Singleton));
    }
    return instance;
}

int main() {
    Singleton* singleton1 = getInstance();
    singleton1->value = 5;
    printf("singleton1 value: %d\n", singleton1->value); // 输出: "singleton1 value: 5"

    Singleton* singleton2 = getInstance();
    printf("singleton2 value: %d\n", singleton2->value); // 输出: "singleton2 value: 5"
    return 0;
}