C ++中的binary_search意外行为 [英] binary_search in c++ unexpected behaviour

问题描述

以下代码段向我返回0.我希望它是1.这是怎么回事?

The following snippet is returning me 0. I expected it to be 1. What's wrong going on here?

#include <iostream>
#include <iterator>
#include <ostream>
#include <algorithm>
#include <vector>
using namespace std;
int main(){
  vector<int> v;
  int arr[] = {10,20,30,40,50};
  v.push_back(11);
  v.push_back(22);
  copy(arr,arr + sizeof(arr)/sizeof(arr[0]),back_inserter(v));  // back_inserter makes space starting from the end of vector v
  for(auto i = v.begin(); i != v.end(); ++i){
    cout << *i << endl;
  }
  cout << endl << "Binary Search -  "  << binary_search(v.begin(), v.end(), 10) <<endl; // returns bool 
}

我正在使用gcc/usr/lib/gcc/i686-linux-gnu/4.6/lto-wrapper

I am using gcc /usr/lib/gcc/i686-linux-gnu/4.6/lto-wrapper

推荐答案

我运行了程序并看到了:

I ran the program and saw this:

11
22
10
20
30
40
50

Binary Search -  0

您的数组未排序，因此二进制搜索失败.(它在第一个位置看到 11 ，并得出结论 10 在这里不存在)

Your array is not sorted, therefore, binary search fails. (it sees 11 in the first position, and concludes 10 does not exist here)

您要么要确保在二进制搜索之前对数组进行排序，要么使用常规的 std :: find .

You either want to ensure the array is sorted before binary searching or use the regular std::find.

这篇关于C ++中的binary_search意外行为的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！