C++基础

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#pragma once
#ifdef _cplusplus
extern "C" {
#endif
void test(int x, int y);
#ifdef __cplusplus
}
#endif

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void change(int&) {
j = 11;
}
int i = 10;
// 10这个内存地址 给了个别名 j
int& j = i;
change(j);
cout << j << endl;

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// C 中
char str1[6] = {'h', 'e', 'l', ''};
char *str2 = "hello";
// C++ #include <string>
string str3 = "hello";
// 调用构造方法
string str4(str3);
string str5("hello");
// malloc = free
// new = delete
// new 数组 = delete[]
string *str6 = new string;
delete str6;
// 拼接字符串
string str5 = str1 + str3;
str1.append(str3);
// 输出
cout << str1.c_str() << endl;
// new 出的字符串
str6->c_str();

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namespace A {
void test() {}
}
// :: 域作用符
A::B::test();
using namespace A::B
test();

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#pragma once
class Instance {
private:
static Instance* instance;
Instance();
public:
static Instance* getInstance();
}

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#include "Instance.h"
Instance * Instance::instance = 0;
Instance::Instance() {
}
Instance* Instance::getInstance() {
if (!instance) {
instance = new Instance;
}
return instance;
}

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#pragma once
class Test1 {
public:
int i;
public:
Text1 operator+(const Test1& t) {
Test1 temp;
temp.i = this->i + t.i;
return temp;
}
}
Test1 test1;
test1.i = 100;
Test1 test2;
test2.i = 200;
// 1.拷贝temp对象给一个临时对象
// 2.临时对象拷贝给test3
// 3.回收临时对象
Test1 test3 = test1 + test2;

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Test2 operator+(const Test1& t1, const Test1& t2) {
Test2 temp;
temp.i = t1.i + t2.i;
return temp;
}

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// 默认 private 私有继承
// 私有继承:父类的 public protected 编程了 private
class Parent {}
class Child : public Parent, private Parent1 {}

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template <typename T>
T max(T a，T b) {
return a > b ? a : b;
}