c - 在二进制数据中搜索文本

Question

我有一个包含文本的二进制数据。文字是已知的。搜索该文本的快速方法是什么:

举个例子。

This is text 1---!@##$%%#^%&!%^$! <= Assume this line is 3 MB of binary dataNow, This is text 2 ---!@##$%%#^%&!%^$! <= Assume this line is 2.5 MB of binary dataThis is text 3 ---

How can I search for text This is text 2.

Currently I'm doing like:

size_t count = 0;
size_t s_len = strlen("This is text 2");

//Assume data_len is length of the data from which text is to be found and data is pointer (char*) to the start of it.
for(; count < data_len; ++count)
{
    if(!memcmp("This is text 2", data + count, s_len)
    {
         printf("%s\n", "Hurray found you...");
    }
}

• 有没有其他更有效的方法来做到这一点
• 将取代 ++count logic与 memchr('T') logic help <= 如果此语句不清楚，请忽略
• memchr 的平均情况大 O 复杂度应该是多少

Answer 1

标准 C 中没有任何东西可以帮助您，但有一个 GNU 扩展 memmem()这样做是这样的:

#define TEXT2 "This is text 2"

char *pos = memmem(data, data_len, TEXT2, sizeof(TEXT2));

if (pos != NULL)
    /* Found it. */

如果您需要移植到没有此功能的系统，您可以采用 memmem() 的 glibc 实现并将其合并到您的程序中。