在二进制数据中查找字符串 [英] Find Character String In Binary Data

问题描述

我有一个二进制文件，我使用NSData对象加载。有没有办法找到一个字符序列，'abcd'，例如，在该二进制数据和返回偏移量，而不将整个文件转换为字符串？似乎应该是一个简单的答案，但我不知道该怎么做。任何想法？

I have a binary file I've loaded using an NSData object. Is there a way to locate a sequence of characters, 'abcd' for example, within that binary data and return the offset without converting the entire file to a string? Seems like it should be a simple answer, but I'm not sure how to do it. Any ideas?

我在iOS 3这样做，所以我没有 -rangeOfData：options：range：可用。

I'm doing this on iOS 3 so I don't have -rangeOfData:options:range: available.

我要授予这个给十六奥多建议strstr。我去找到C函数strstr的源代码，并重写它工作在一个固定长度的字节数组 - 这意味着不同于一个char数组，因为它不是null终止。这里是我最后得到的代码：

I'm going to award this one to Sixteen Otto for suggesting strstr. I went and found the source code for the C function strstr and rewrote it to work on a fixed length Byte array--which incidentally is different from a char array as it is not null terminated. Here is the code I ended up with:

- (Byte*)offsetOfBytes:(Byte*)bytes inBuffer:(const Byte*)buffer ofLength:(int)len;
{
    Byte *cp = bytes;
    Byte *s1, *s2;

    if ( !*buffer )
        return bytes;

    int i = 0;
    for (i=0; i < len; ++i)
    {
        s1 = cp;
        s2 = (Byte*)buffer;

        while ( *s1 && *s2 && !(*s1-*s2) )
            s1++, s2++;

        if (!*s2)
            return cp;

        cp++;
    }

    return NULL;
}

这会返回一个指向第一个字节的指针，在缓冲区中寻找应该包含字节的字节数组。

This returns a pointer to the first occurrence of bytes, the thing I'm looking for, in buffer, the byte array that should contain bytes.

我这样调用：

// data is the NSData object
const Byte *bytes = [data bytes];
Byte* index = [self offsetOfBytes:tag inBuffer:bytes ofLength:[data length]];

推荐答案

将子字符串转换为 NSData 对象，并使用 NSData library / documentation / Cocoa / Reference / Foundation / Classes / NSData_Class / Reference / Reference.html＃// apple_ref / occ / instm / NSData / rangeOfData：options：range：rel =nofollow noreferrer> rangeOfData：options：range： 。确保字符串编码匹配！

Convert your substring to an NSData object, and search for those bytes in the larger NSData using rangeOfData:options:range:. Make sure that the string encodings match!

在iPhone上，如果不可用，您可能需要自己做。 C函数 strstr（）将为您提供指向缓冲区中第一次出现的模式的指针（只要不包含空值！），而不是索引。这是一个函数，应该做这项工作（但没有承诺，因为我没有试过实际运行它...）：

On iPhone, where that isn't available, you may have to do this yourself. The C function strstr() will give you a pointer to the first occurrence of a pattern within the buffer (as long as neither contain nulls!), but not the index. Here's a function that should do the job (but no promises, since I haven't tried actually running it...):

- (NSUInteger)indexOfData:(NSData*)needle inData:(NSData*)haystack
{
    const void* needleBytes = [needle bytes];
    const void* haystackBytes = [haystack bytes];

    // walk the length of the buffer, looking for a byte that matches the start
    // of the pattern; we can skip (|needle|-1) bytes at the end, since we can't
    // have a match that's shorter than needle itself
    for (NSUInteger i=0; i < [haystack length]-[needle length]+1; i++)
    {
        // walk needle's bytes while they still match the bytes of haystack
        // starting at i; if we walk off the end of needle, we found a match
        NSUInteger j=0;
        while (j < [needle length] && needleBytes[j] == haystackBytes[i+j])
        {
            j++;
        }
        if (j == [needle length])
        {
            return i;
        }
    }
    return NSNotFound;
}

这样运行像O（nm），其中n是缓冲区长度，m是子字符串的大小。它写成使用 NSData ，因为两个原因：1）这是你看起来有在手，和2）这些对象已经封装了实际的字节，和长度缓冲区。

This runs in something like O(nm), where n is the buffer length, and m is the size of the substring. It's written to work with NSData for two reasons: 1) that's what you seem to have in hand, and 2) those objects already encapsulate both the actual bytes, and the length of the buffer.

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