高品位代码集

博客链接: http://codeshold.me/2017/02/c_code_sinped.html

编程的品味也有高低之分

1. 单链表元素删除操作

参考

• 低品位

    remove_list_entry(entry)
    {
        prev = NULL;
        walk = entry;
  
        // Walk the list
        while(walk != entry) {
            prev = walk;
            walk = walk->next;
        }
  
        // Removing the entry by updating the previous or the head entry
        if(prev) {
            prev->next = entry->next;
        } else {
            head = entry->next;
        }
    }
  

• 高品位

    remove_list_entry(entry)
    {
        // The "indirect" pointer points to the ADDRESS of the thing we'll update
        indirect = &head;
  
        // Walk the list, looking for the thing points to the entry we want to remove
        while(*indirect != entry) {
            indirect = &(*indirect)->next;
        }
  
        // Remove the entry...
        *indirect = entry->next;
    }
  

2. 类型选择对程序执行时间的影响

参考

• g++ test_int.cpp -O3 编译运行

    #include <cstdio>
    #include <math.h>
    #include <ctime>
  
    #define NN 1000000
  
    int main()
    {
        int t=clock();
        long long sum=0;
  
        // 低品位, 运行时间明显长
        for(long long a=1;a<=NN;a++)
            for(long long b=1;b<=sqrt(NN);b++)
                sum+=(a/b)*(a/b);
  
        printf("%lld,%dn",sum,clock()-t);
  
        t=clock();
        sum=0;
  
        // 高品位, 运行时间明显短
        for(int a=1;a<=NN;a++)
            for(int b=1;b<=sqrt(NN);b++)
                sum+=(long long)(a/b)*(a/b);
  
        printf("%lld,%dn",sum,clock()-t);
    }