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c++ syntax

admin 11月 14, 2020 0

This article records my C++ learning notes, keeps developing…

Chinese Version: 这篇文章记录我对C++学习心得和基本使用方法，以便以后手生的时候快速上手。

Template

C++用template来实现Java中generic class的功能

注意问题：

test.h里面声明类Circle，test.cpp中的每一个member function前面都要申明。

template<class K, class V> class Circle{}；

Array

C++中Array的长度没有像Java一样封装，一定要自己设置一个变量去约束。常用做法：

int array[20] = malloc(20*sizeof(int)) --提前分配出空间，不然容易出现指针为NULL的异常

Pointer

Basic Intuition:

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int n = 3；

-- p_n stores the address of n; * is declaring pointer; & is reference operator
int* p_n = &n; 

-- m stores value 3; * is dereference operator
int m = *p_n;

Pointer & Array

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int* p_array = int array[20];	
int* p_array = new int[20];

Circle** p_array = new Circle*[20];

注意！Circle* p_array = new Circle[20] 创建的是一个包含Circle整个实例的数列，需要有Circle里面有default constructor.

String Comparision

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char nts1[] = "Test";
char nts2[] = "Test”;

The value of ptr_hash(nts1)==ptr_hash(nts2) is false. Cause, you are hashing two different string pointers pointing to same string.

Read File by Word

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#include <iostream>
#include <fstream>
using namespace std;

int  () {
 		ifstream myfile;
 		myfile.open ("ants-sample-data/antsin");
 		string line;
 		if (myfile.is_open()){
      		for(int i = 0; myfile >> line; i++) 
     			cout << line << 'n';
   		myfile.close();
 		}
 		else cout << "Unable to open file"; 
 		return 0;
}

Calculate Funtion Runtime

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#include <time.h>
clock_t t = clock();

function_to_measured();

t = clock() - t;
total_runtime += ((float)t)/CLOCKS_PER_SEC;

Class

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class Circle{
   	private:
    	int height = 2; 
    	-- Wrong! Only static const integral data members can be initialised within a class.
    	public:
    	…
}
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