Question

我正在尝试用C语言实现Boyer-Moore算法来搜索.pcap文件中的特定单词。我引用了http://ideone.com/FhJok5中的代码。我正在使用这个代码。

我正在将数据包作为字符串传递，而我正在搜索的关键字是函数search（）。当我运行我的代码时，它每次都会给出不同的值。有时它也给出了正确的价值。但大多数时候它没有确定一些价值观。

我已经从Naive Algo Implementation获得了结果。结果总是很完美。

我在VMware 10.0.1上使用Ubuntu 12.0.4。郎：C

我的问题是每次都必须给出相同的结果吗？无论对错。每次在相同输入上运行文件时，此输出都会不断变化;在几次运行中，它也给出了正确的答案。大多数情况下，该值在3或4个值之间变化。

对于调试我到目前为止做了：

每次传递字符串而不是数据包，每次都是完美且相同且正确的值。
检查pcap部分，我可以看到所有数据包都被传递给该函数（我通过打印数据包帧检查没有）。
我发送给Naive Algo代码的相同数据包，它提供了完美的代码。

请给我一些想法，可能是什么问题。我怀疑内存管理有些问题。但如何找到哪一个？

提前致谢。

# include <limits.h>
# include <string.h>
# include <stdio.h>

# define NO_OF_CHARS 256

// A utility function to get maximum of two integers
int max (int a, int b) { return (a > b)? a: b; }

// The preprocessing function for Boyer Moore's bad character heuristic
void badCharHeuristic( char *str, int size, int badchar[NO_OF_CHARS])
{
    int i;

    // Initialize all occurrences as -1
    for (i = 0; i < NO_OF_CHARS; i++)
         badchar[i] = -1;

    // Fill the actual value of last occurrence of a character
    for (i = 0; i < size; i++)
         badchar[(int) str[i]] = i;
}

/* A pattern searching function that uses Bad Character Heuristic of
   Boyer Moore Algorithm */
void search( char *txt,  char *pat)
{
    int m = strlen(pat);
    int n = strlen(txt);

    int badchar[NO_OF_CHARS];

    /* Fill the bad character array by calling the preprocessing
       function badCharHeuristic() for given pattern */
    badCharHeuristic(pat, m, badchar);

    int s = 0;  // s is shift of the pattern with respect to text
    while(s <= (n - m))
    {
        int j = m-1;

        /* Keep reducing index j of pattern while characters of
           pattern and text are matching at this shift s */
        while(j >= 0 && pat[j] == txt[s+j])
            j--;

        /* If the pattern is present at current shift, then index j
           will become -1 after the above loop */
        if (j < 0)
        {
            printf("\n pattern occurs at shift = %d", s);

            /* Shift the pattern so that the next character in text
               aligns with the last occurrence of it in pattern.
               The condition s+m < n is necessary for the case when
               pattern occurs at the end of text */
            s += (s+m < n)? m-badchar[txt[s+m]] : 1;

        }

        else
            /* Shift the pattern so that the bad character in text
               aligns with the last occurrence of it in pattern. The
               max function is used to make sure that we get a positive
               shift. We may get a negative shift if the last occurrence
               of bad character in pattern is on the right side of the
               current character. */
            s += max(1, j - badchar[txt[s+j]]);
    }
}

/* Driver program to test above function */
int main()
{
    char txt[] = "ABAAAABAACD";
    char pat[] = "AA";
    search(txt, pat);
    return 0;

Boyer-Moore算法

0 个答案: