两个函数之间的时间差。

I have two simple code functions that compare two strings.

我有两个简单的代码函数来比较两个字符串。

The strategy is to compare a short string with a long string sequentially.

策略是按顺序比较短字符串和长字符串。

For example,

例如,

string1 = "ABCDABCDEFGAHAD",
string2 = "ABCD"

then compare string1 and string2 by sliding string2 until string2's end is reached to string1's end

然后通过滑动string2比较string1和string2，直到string2的末端到达string1的末端。

Here are the functions that I used First one is

这里是我使用的第一个函数。

void compare1(char* src , char* target , int src_size , int target_size , int* score){
   int i , j;
   for ( i = 0 ; i < src_size - target_size ; i++){
         for(j=0; j < target_size ; j++){
               if(src[i+j] == target[j]){
                    score[i]++;
               }else{
                     continue;
               }
         }
   }
}

and the second one is

第二个是。

void compare2(char* src , char* target , int src_size , int target_size , int* score){
       int i , j;
       char* dest = (char*)malloc(sizeof(char)*(target_size));
       for( i = 0 ; i < src_size - target_size ; i++){
            strncpy(dest,src,target_size);
            for( j = 0 ; j < src_size ; j++){
                if(dest[j] == target[j]){
                    score[i]++;
                }else{
                    continue;
                }
            }
        }
        free(dest);
    }

These two gave me different times, which are

这两个给了我不同的时间。

8393.00 ms from compare1 
4415.00 ms from compare2

what makes this time difference?

是什么造成了时差?

the length of two strings are 1024*1024*10 and 128 with respect to src and target in function variable.

两个字符串的长度是1024*1024*10和128关于src和函数变量的目标。

1 个解决方案

#1

Your second function is wrong. It should copy from src + i not from src. Also the nested loop should be done for the target_size elements of dest, not for src_size as in your code. This results in:

你的第二个功能是错误的。它应该从src + i复制而不是src。还应该为target_size元素执行嵌套循环，而不是在代码中使用src_size。这将导致:

void compare2(char* src , char* target , int src_size , int target_size , int* score){
       int i , j;
       char* dest = (char*)malloc(sizeof(char)*(target_size));
       for( i = 0 ; i < src_size - target_size ; i++){
            strncpy(dest,src + i,target_size);
            for( j = 0 ; j < target_size ; j++){
                if(dest[j] == target[j]){
                    score[i]++;
                }else{
                    continue;
                }
            }
        }
        free(dest);
    }

Remark 1: the else continue; is useless ! Remark 2: you can use memcpy to copy the string (since you know the length and don't use the terminal character '\0').

注1:else继续;是无用的!备注2:您可以使用memcpy来复制字符串(因为您知道长度并且不使用终端字符'\0')。