Search through a (large) binary file.
in [CSharp]
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From: Michelle on 12 Sep 2009 02:21 Peter, Thank you for the explanation. It's more difficult then I thought. I thought that searching through binary data a common issue was (you can do this with every hex editor) and that there were plenty of examples available. For me there is only a single pattern to match, I don't need to search for multiple patterns in a single pass. Speed is not the main issue (although it's important), but finding everything is the main issue. To try your example, I created a console application (using Visual Studio 2008) Maybe it's a little bit silly, but how can I add my pattern (hex value) as an argument to FindByteString -> byte[] rgbPattern? > int FindByteString(string strInputFile, byte[] rgbPattern) Get an error on this and don't know how to solve it: > if (++ibOffset < cbBlockCur.Length) > 'int' does not contain a definition for 'Length' and no extension method 'Length' accepting a first argument of type 'int' could be found (are you missing a using directive or an assembly reference?) As mentioned before, I'm a rookie using C#, so please be patient. But I'm willing to learn. Regards, Michelle
From: Peter Duniho on 12 Sep 2009 03:23 On Fri, 11 Sep 2009 23:21:24 -0700, Michelle <michelle(a)notvalid.nomail> wrote: > Peter, > > Thank you for the explanation. It's more difficult then I thought. > I thought that searching through binary data a common issue was (you can > do > this with every hex editor) and that there were plenty of examples > available. I don't know about the relative quantity of examples one way or the other. As far as it being a common feature in hex editors, well...a) not all hex editors are created equal (any editor that requires the entire file data to be loaded into memory at once, which is a lot of them, can trivially search the entire file contents without worrying about the block-level i/o), and b) for someone with enough programming experience to be able to write a good hex editor, this really isn't a very difficult problem. > [...] > To try your example, I created a console application (using Visual > Studio 2008) > Maybe it's a little bit silly, but how can I add my pattern (hex value) > as > an argument to FindByteString -> byte[] rgbPattern? The same way you'd initialize any array. For example: byte[] rgbPattern = { 0xff, 0x56, 0x13, 0x1a }; If you want to provide a text string as initialization, that's possible as well. You'll just have to parse each pair of hex digits in the string as a byte and add them to an appropriate array. For example: string strPattern = "ff56131a"; byte[] rgbPattern = RgbFromString(strPattern); where: byte[] RgbFromString(string strPattern) { byte[] rgbRet = new byte[strPattern.Length / 2]; for (int ib = 0; ib < rgbRet.Length; ib++) { rgbRet[ib] = byte.Parse(strPattern.Substring(ib * 2, 2), NumberStyles.HexNumber); } return rgbRet; } > >> int FindByteString(string strInputFile, byte[] rgbPattern) > > Get an error on this and don't know how to solve it: >> if (++ibOffset < cbBlockCur.Length) >> > > 'int' does not contain a definition for 'Length' and no extension method > 'Length' accepting a first argument of type 'int' could be found (are you > missing a using directive or an assembly reference?) > > As mentioned before, I'm a rookie using C#, so please be patient. > But I'm willing to learn. For what it's worth, it's my opinion that one of the best ways to learn programming is to read other people's code and figure out how it works. And of course, if you do that, in the process you should be able to figure out how to fix any parts of the code that might not be exactly correct. As far as that specific error goes, the purpose of that line of code is simply to continue the loop if there are still unprocessed bytes left in the current block (all of the rest of the code in the loop, after that "if" statement and its block, handles updating the in-memory blocks holding the data being processed to the next block-size part of the file). Knowing that, it should be clear that the correct statement is: if (++ibOffset < cbBlockCur) That is, just remove the ".Length"...it's superfluous and left over from a variation of the code I had before I changed it and posted my message. Hope that helps. Pete
From: Michelle on 12 Sep 2009 05:57 Rossum, I spend some time reading about the mentioned algorithms. The "Boyer-Moore Algorithm" seems to be the most popular and fastest. (Also used in several hex editors). Unfortunately (so far) I couldn't find a c# example for searching binary files. Because I've not much experience using C#, it's difficult to translate the 'theory' to a working example. So if you know one, I appreciate a link to it. I'd like to read other people's code and figure out how it works to learn about. (It's for education only :-)) ) Regards, Michelle
From: Michelle on 12 Sep 2009 06:39 Peter, It's a shame, but i can't get it to work. I'm stuck with this error: "An object reference is required for the non-static field, method, or property 'binSearch.Program.FindByteString(string, byte[])'" I tried several solutions found, but no luck so far. namespace binSearch { class Program { static void Main(string[] args) { byte[] rgbPattern = { 0xFF, 0x56, 0x13, 0x1A, 0x1B, 0x08, 0x7B, 0x15, 0x61, 0x08, 0x00, 0x15, 0x1E }; FindByteString(@"D:\BinarySearch\myfile.bin"); } int FindByteString(string strInputFile, byte[] rgbPattern) { byte[] rgbBlockCur = new byte[4096], [. . .] Michelle
From: Tom Spink on 12 Sep 2009 07:56
Michelle wrote: > Peter, > > It's a shame, but i can't get it to work. > I'm stuck with this error: "An object reference is required for the > non-static field, method, or property > 'binSearch.Program.FindByteString(string, byte[])'" > I tried several solutions found, but no luck so far. > > namespace binSearch > { > class Program > { > static void Main(string[] args) > { > byte[] rgbPattern = { 0xFF, 0x56, 0x13, 0x1A, 0x1B, 0x08, 0x7B, > 0x15, 0x61, 0x08, 0x00, 0x15, 0x1E }; > FindByteString(@"D:\BinarySearch\myfile.bin"); > } > int FindByteString(string strInputFile, byte[] rgbPattern) > { > byte[] rgbBlockCur = new byte[4096], > [. . .] > > Michelle You need to qualify the method definition with the static keyword: /// static int FindByteString(string strInputFile, byte[] rgbPattern) /// Put the keyword 'static' before the 'int', and it should remove that error. It's probably best if you know why... so I suggest a bit of research on the 'static' keyword and what static members are. -- Tom |