Code Reading

0 why

The purpose of this blog is to write down some useful tips in coding. 

1 starting point of code:

• c/c++: main
• java: static void main
• Microsoft windows: WinMain
• Java applet or servlet hosts: init

2 基本流程/操作中的tips

this tip can make the if condition more concise

• && / and: only evaluate the righthand side when the lefthand side is evaluated as "true".
• || / false: only evaluate the righthand side when the lefthand side is evaluated as "false".
  • eg: fragment from ECHO

    if (*++argv && !strcmp(*argv, "-n")){
        ...
    }

assignment expression(赋值表达式) in a logic express
• int c = 0;
• while ((c = getopt (argc, argv, "t: "))  != -1)   // first execute assignment expression, and compare the lefthand variable with "-1"(a possible return value of getopt, which means the end of parsing in getopt.)

3 static

 https://www.runoob.com/w3cnote/cpp-static-usage.html

static 通常被认为同时具备全局和封装的特性。原因如下：

• 在普通的面向过程编程中，如果需要定义一个可供下次调用的变量时（使得变量在函数外依然有效），不选择全局变量而选择static要更好。原因是static的作用范围可以限制在文件内

#include <iostream>                                                                                                                                                                                                                    
static int i;                                                                                                                                                                                                                                
void Print(){                                                                                                                                                                                                                                
    std::cout << "The " << ++ i << "th times call of Print()
";                                                                                                                                                                             
}                                                                                                                                                                                                                                             
void Test() {                                                                                                                                                                                                                                
    for (int i=0; i < 10; ++ i) {
        Print();
    }
}
int main(){
    i = 0;
    Test();
    return 0;
}

• 在面向过程的编程中，如果要在类对象之间共享一些数据，需要将变量定义为static类型

// MyTest.h
class MyTest {
public:
    MyTest();
    ~MyTest();

    void Print();

private:
    static int number_of_object;
};


// MyTest.cpp
#include "../include/MyTest.h"
#include <iostream>

int MyTest::number_of_object = 0;
MyTest::MyTest() {
    ++ number_of_object;
}
MyTest::~MyTest() {

}
void MyTest::Print() {
    std::cout << "number_of_object = " << number_of_object << std::endl;   
}

// main.cpp
#include "./include/MyTest.h"

void Test(){
    for (int i=0; i<10; ++ i) {
        MyTest t1;
        t1.Print();
    }    
}
int main() {
    Test();
    return 0;
}

4 template class: 模板类