bsearch代码实现

二分查找完整代码：

#include<iostream>

using namespace std; 

void * bsearch(const void *key, const void *base, size_t nel, size_t width, int (*cmp)(const void *, const void *)){ 
    void *mid = NULL; 
    int sign; 
    while (nel > 0) { 
         
        mid = (char *)base + width*(nel/2); 
        sign = cmp(key, mid); 
        if (sign == 0) return mid;//找到  
        if (nel == 1) break; 
        else if (sign < 0) 
            nel /= 2;//下取整  
        else { 
            base = mid; 
            nel -= nel/2;//上取整  
        } 
         
    } 
    return NULL; 
} 

int compare(const void *val1, const void *val2) { 
    int iVal1 = *(int*)val1; 
    int iVal2 = *(int*)val2; 
    if (iVal1 > iVal2) { 
        return 1; 
    } 
    else if (iVal1 == iVal2) { 
        return 0; 
    } 
    return -1; 
}