C++功能实现

1、获取随机数
2、判断当前系统字节序
3、关键字volatile的使用
4、自加操作符重载
5、使用流迭代器输出字符串

6、使用格式化日期时间
7、简单类对象存入文件

获取随机数

#include <cstdio> //标准(std)输入输出(io)库, 内含printf()函数#include <cstdlib> //标准(std)操作库(lib), 内含srand(),rand()函数#include <ctime> //时间库 (time), 内含time()系统时间函数#include <iostream>using std::cout;using std::endl;int GetRandom(int iLowBoundary, int iHighBoundary){ //通过系统时间初始化随机数种子,time_t time(time_t* _Time) //如果不设置随机数种子,则每次rand()函数的起始值都一样. srand((unsigned)time(NULL)); // rand()为随机数函数, 产生[0,int型最大值)之间的整数数 //此值依系统不同而不同, 一般为2147483648, 可认为无穷 // 通过rand() % (iHighBoundary - iLowBoundary + 1) + iLowBoundary转化为[iLowBoundary, iHighBoundary]之间的整数 //(注:rand()%(iHighBoundary + 1)产生[0,iHighBoundary]之间的整数) int n = rand() % (iHighBoundary - iLowBoundary + 1) + iLowBoundary; return n;}int main(){ while (true) { cout << GetRandom(1, 10) << endl; system("PAUSE"); }}

 

判断当前系统字节序

bool IsLittleEndian(){ int i = 1; char* pChar = reinterpret_cast<char*>(&i); return *pChar == 1;}bool IsBigEndian() // 1-小端（Intel）; 0-大端(Motor) { union { long l; char psz[sizeof(long)]; } u = {1}; return 1 == u.psz[sizeof(long) - 1];} int main(){ cout << IsLittleEndian() << endl; cout << IsBigEndian() << endl;}

 

关键字volatile的使用

 #include <iostream>using namespace std;int main(){ const int i = 1; volatile const int j = 1; int* m = const_cast<int*>(&i); *m = 2; // 改变i的值 int* n = const_cast<int*>(&j); *n = 2; // 改变j的值 cout << i << endl; // 输出1，因为编译器进行了暂存优化，所以输出原值 cout << j << endl; // 输出2，关键字volatile不进行优化，输出新值}

 

自加操作符重载

#include <iostream>using namespace std;class tt{public: int i; tt() :i(0) { } tt& tt::operator++() { i = i + 1; return *this; } tt tt::operator++(int m) { tt tmp(*this); i = i + 1; return tmp; }};int main(){ tt t; cout << (++t).i; cout << t.i; cout << (t++).i; cout << t.i;}

 

使用流迭代器输出字符串

#include<iostream>#include<string>#include<iterator>using namespace std;ostream_iterator<string> oo(cout);int main(){ *oo="Hello,"; ++oo; *oo="world!/n"; return 0;}

 

使用格式化日期时间

 #include <iostream>#include <ctime>using std::cout;using std::endl;void main(){ // 设置区域为中国 //setlocale(LC_TIME, "chs"); // 获取当前日期时间 time_t currentTime = time(NULL); tm* tmCurrentTime = localtime(¤tTime); // 使用asctime获取日期时间字符串， 此函数不受locale的影响，格式也是固定的 char* pszTime = asctime(tmCurrentTime); cout << "Current time is: " << pszTime << endl; // 获取20天后的日期 unsigned long ulTimeOffset = 20 * 24 * 60 * 60; time_t time20 = currentTime + ulTimeOffset; tmCurrentTime = localtime(&time20); pszTime = asctime(tmCurrentTime); cout << "The date after 20 days is: " << pszTime << endl; // 使用strftime格式化日期时间， 此函数受locale的影响，可自定义格式格式 char buffer[81] = {0,}; strftime(buffer, sizeof(buffer)-1, "%#c", tmCurrentTime); // 当前区域的长日期和时间缩写表示，例如："Tuesday, March 14, 1995, 12:41:29"。 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#x", tmCurrentTime); // 当前区域的长日期缩写表示，例如："Tuesday, March 14, 1995".。 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#a", tmCurrentTime); // 星期几的缩写 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#A", tmCurrentTime); // 星期几的全称 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#b", tmCurrentTime); // 月份的缩写 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#B", tmCurrentTime); // 月份的全称 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#p", tmCurrentTime); // Current locale's A.M./P.M. indicator for 12-hour clock cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#X", tmCurrentTime); // 当前区域的时间表示 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#z", tmCurrentTime); // 时区名或时区缩写，依赖于已注册的设置：位置时区为空字符串 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#Z", tmCurrentTime); // 同上 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#%", tmCurrentTime); // 百分号标记 cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#d", tmCurrentTime); // 日期的十进制表示 (01 – 31) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#H", tmCurrentTime); // 小时，24小时表示法 (00 – 23) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#I", tmCurrentTime); // 小时，12小时表示法(01 – 12) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#j", tmCurrentTime); // 一年中天数 (001 – 366) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#m", tmCurrentTime); // 十进制月份 (01 – 12) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#M", tmCurrentTime); // 十进制分钟 (00 – 59) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#S", tmCurrentTime); // 十进制秒数 (00 – 59) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#U", tmCurrentTime); // 十进制数表示一年中的第几个星期, 星期日是一周的第一天 (00 – 53) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#w", tmCurrentTime); // 星期几的十进制表示 (0 – 6; Sunday is 0) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#W", tmCurrentTime); // 十进制数表示一年中的第几个星期, 星期一是一周的第一天 (00 – 53) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#y", tmCurrentTime); // 十进制数表示世纪中的第几年 (00 – 99) cout << "Format date is: " << buffer << endl; strftime(buffer, sizeof(buffer)-1, "%#Y", tmCurrentTime); // 十进制数表示年份 cout << "Format date is: " << buffer << endl;}

 

简单类对象存入文件

#include <iostream>#include <fstream>#include <cstdlib>using std::cout;using std::endl;using std::ofstream;using std::istream;using std::ios_base;class Data {friend ofstream& operator<<(ofstream& outFile, Data& data){ if (outFile.is_open()) { outFile << data._cmd; outFile.write(reinterpret_cast<char*>(&data._op1), 20); outFile.write(reinterpret_cast<char*>(&data._op2), 1); } return outFile;}friend ifstream& operator>>(ifstream& inFile, Data& data){ if (inFile.is_open()) { inFile >> data._cmd; char buffer[20] = {0, }; inFile.read(buffer, 20); memcpy(data._op1, buffer, 20); inFile.read(buffer, 1); memcpy(&data._op2, buffer, 1); } return inFile;}public: Data() : _cmd(1), _op2('b') { memset(_op1, 'a', 20); }private: int _cmd; char _op1[20]; char _op2;}; int main(){ Data d, e; ofstream outFile("file.txt", ios_base::binary); outFile << d; outFile.close(); ifstream inFile("file.txt", ios_base::binary); inFile >> e; inFile.close();}