用 void* 编写泛型函数

1.泛型交换

//1.编写int类型的swap
void swap(int *vp1, int *vp2) {
    int a = *vp1;
    *vp1 = *vp2;
    *vp2 = a;
}
//2.引申至泛型swap
void swap(void *vp1, void *vp2, int size){
    char buffer[size];
    memcpy(buffer, vp1, size);
    memcpy(vp1, vp2, size);
    memcpy(vp2, buffer, size);
}

使用泛型swap交换C-string:

char* husband = "Fred";
char* wife = "Wilma";
swap(&husband,&wife,sizeof(char));

2.泛型线性搜索

//1.编写int类型的lsearch
int * lsearch(int key ,int* array, int size){
    for (int i = 0; i < size; i++)  
    {
        if(array[i] == key)
            return i;
    }
    return NULL;
}
//2.编写泛型lsearch
int *lsearch(void *key, void *base, int size, int elementSize){
    for (int i = 0; i < size; i++) {
      void * elemAddr = (char *)base + i * elemSize; 
      if (memcmp(key, elemAddr, elemSize) == 0)
        return elemAddr;
    }       
    return NULL;
}

如果用泛型lsearch来搜索C-string，因为C-string的长度不是固定的，故无法利用memcmp进行比较。可以利用函数指针实现：

int *lsearch(void *key, void *base, int size, int elementSize,int (*cmpFunc)(void *,void *)){
    for (int i = 0; i < size; i++) {
      void * elemAddr = (char *)base + i * elemSize; 
      if (cmpFunc(key, elemAddr) == 0)
        return elemAddr;
    }       
    return NULL;
}

实现cmpFunc:

//比较int
int intCmp(void *elem1,void *elem2){
    int *ip1 = elem1;
    int *ip2 = elelm2;
    return *ip1-*ip2;
}
//比较C-string
int strCmp(void *elem1,void *elem2){
    char *s1 = *(char**)elem1;
    char *s2 = *(char**)elem2;
    return strcmp(s1,s2);
}

3.泛型二分搜索

void *binary_search(void *key,void *base,int n,int elemSize,int (*cmpFunc)(void *,void *)){
    int low = 0;
    int high = n-1;
    while(low <= high){    
        int mid = low+(high-low)/2;
        void *midAddr = (char*)base+mid*elemSize;
        if(cmpFunc(key,midAddr) == 0){
            return midAddr;
        }
        else if(cmpFunc(key,midAddr) < 0){
            high = mid-1;
        }
        else{
            low = mid+1;
        }
    }
    return NULL;
}

编码验证:

#include<iostream>
using namespace std;

int intCmp(void *elem1,void *elem2){
    int *ip1 = (int*)elem1;
    int *ip2 = (int*)elem2;
    return *ip1-*ip2;
}

void *binary_search(void *key,void *base,int n,int elemSize,int (*cmpFunc)(void *,void *)){
    int low = 0;
    int high = n-1;
    while(low <= high){
        int mid = low+(high-low)/2;
        void *midAddr = (char*)base+mid*elemSize;
        if(cmpFunc(key,midAddr) == 0){
            return midAddr;
        }
        else if(cmpFunc(key,midAddr) < 0){
            high = mid-1;
        }
        else{
            low = mid+1;
        }
    }
    return NULL;
}

int main(){
    int a[]={1,2,3,4,5,6,7,8,9};
    int i;
    for(i=1;i<10;i++){
    
        cout<<((int*)binary_search(&i,a,9,sizeof(int),intCmp))<<endl;        
    }    
    return 0; 
} 

运行截图: