C++ - 随机数生成器(random-number generator) 的 详解 及 代码

随机数生成器(random-number generator) 的 详解 及 代码

本文地址: http://blog.csdn.net/caroline_wendy/article/details/17322165
随机数, C语言的函数是rand(), C++则是随机数生成器(random-number generator) = 分布对象(distribution object) + 引擎(engine);
使函数每次生成不同的随机数, 需要使用静态(static)局部变量, 这样分布对象和引擎就能保持(hold)状态(state), 每次都生成一个新的;
生成随机的整数, 使用分布对象uniform_int_distribution<>, 默认模板参数是int;
生成随机的浮点数, 使用分布对象uniform_real_distribution<>, 默认模板参数是double;

代码:

#include <iostream> #include <vector> #include <string> #include <random>   using namespace std;  std::vector<unsigned> good_randVec() { 	static std::default_random_engine e; //静态 	static std::uniform_int_distribution<unsigned> u(0,9); //静态 	std::vector<unsigned> ret; 	for(size_t i=0; i<10; ++i) 		ret.push_back(u(e)); 	return ret; }  int main() { 	std::default_random_engine e; 	std::cout << "engine : "; 	for(size_t i=0; i<10; ++i) 		std::cout << e() << " "; 	std::cout << std::endl;  	std::cout << "uniform : "; 	std::uniform_int_distribution<unsigned> u(0, 9); //即[0, 9] 	for(size_t i=0; i<10; ++i) 		std::cout << u(e) << " "; 	std::cout << std::endl;  	std::cout << "min : " << e.min() << " max : " << e.max() << std::endl;  	std::vector<unsigned> v1(good_randVec()); 	std::vector<unsigned> v2(good_randVec()); 	for(size_t i=0; i<v1.size(); ++i) 		std::cout << v1[i] << " "; 	std::cout << std::endl; 	for(size_t i=0; i<v2.size(); ++i) 		std::cout << v2[i] << " "; 	std::cout << std::endl;  	std::uniform_real_distribution<double> ud(0, 1); 	std::cout << "float : "; 	for(size_t i=0; i<10; ++i) 		std::cout << ud(e) << " "; 	std::cout << std::endl;  	return 0; }

输出:

engine : 16807 282475249 1622650073 984943658 1144108930 470211272 101027544 1457850878 1458777923 2007237709  uniform : 3 5 8 0 0 5 6 0 3 0  min : 1 max : 2147483646 0 1 7 4 5 2 0 6 6 9  3 5 8 0 0 5 6 0 3 0  float : 0.686773 0.930436 0.526929 0.653919 0.701191 0.762198 0.0474645 0.328234 0.75641 0.365339

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