[分享] 亂數產生器的好幫手 generate_n
有時候我們在寫測試程式時，需要產生一些亂數資料 eq.排序
最簡單的方式就是用迴圈
for(int i=0;i<N;i++)
a[i] = rand_num_gen();
STL 提供了很簡潔的語法 (reference by Thinking in C++)
generate_n(a,N,rand_num_gen);
以下是簡單的產生 1~100 之間的亂數到 a 陣列的範例程式:
==========================================================
#include <ctime>
#include <cstdlib>
#include <cassert>
#include <algorithm>
#include <iterator>
#include <iostream>
using namespace std;
class RandGen
{
int l_; int h_;
public:
RandGen(int l,int h): l_(l), h_(h){
assert(l_ < h_);
srand((unsigned)time(0));
}
int operator() (){
int range=(h_-l_)+1;
return l_ + static_cast<int>(range*rand()/(RAND_MAX + 1.0));
}
};
int main()
{
const int N = 20;
int a[N];
generate_n(a,N,RandGen(1,100));
copy(a,a+N,ostream_iterator<int>(cout," "));
}
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