[c#] searching for a hex string in a file?

[SkyyPunk Veteran]

I have a program im working on to extract pngs (and later on more files) ...but currently i am using BinaryReader, and i read it byte-by-byte to check for png header/footer. For most files (even those over just a few hundred kb) it takes a little bit.

is there any way to just search in the file for what im looking for, or any ideas on a faster way to do this?

it does *work* the way i am doing it...its just slow :)

Thanks

Doug

[nvme]

im thinking you're still going to have to do a sequential search and if the files are large and the part you're searching for is far enough in the file, that's going to take a while. that is if im understanding you correctly with what you are trying to do.

(edit) is the method you're using to read the data in reading in large chunks from the file.. or is it reading a byte then comparing it and then reading the next byte. if it's the latter, that could be causing your slow down.

[SkyyPunk Veteran]

  nvme said:

im thinking you're still going to have to do a sequential search and if the files are large and the part you're searching for is far enough in the file, that's going to take a while. that is if im understanding you correctly with what you are trying to do.

(edit) is the method you're using to read the data in reading in large chunks from the file.. or is it reading a byte then comparing it and then reading the next byte. if it's the latter, that could be causing your slow down.

well ive tried two ways, reading a byte at a time, and reading 100 bytes, then using string comparisons with that chunk...

i have a string var with the hex im looking for

as i go, i have a pos var

if the byte looked at is = the first two in the hex string, it increments, and it resets to 0 if the byte is different than expected...then it just stores each byte once it finds the header until the footer, then it writes that file, then clears the previous stuff

[Doli]

ok this is old, i made this about 2 years ago and i think there are better ways to do this. The code gets an jpeg image (album art) in an mp3 file, it works but as you can see the hex values i was looking for are 41h,50h,49h,43h ( APIC ). I used filestream not binaryreader. You can give it a try and fix it up to work with your code. Just change the conditions in the "data == 0x41 %% ........" to what your looking for. There may be a better way but i was still learning back then (C# and mp3 ID tag stuff) and i havent changed anything since.

returns true if there is data and "out Img" get the Image, false if no image data and "out Img" get null.

public bool GetImageFromMp3( string Mp3_File_Path, out Image Img )
		{			  
			int imgPos = 0;
			int imgEnd = 0;
			int imgLenght = 0;
			FileStream fs = new FileStream( Mp3_File_Path, FileMode.Open );
			byte [] data = new byte [ fs.Length ];
			fs.Read( data, 0, (int)fs.Length );
			for (int i = 0; i < data.Length; i++)
			{
				if (data[i]   == 0x41 &&	  //APIC  0x41 0x50 0x49 0x43
					data[i+1] == 0x50 &&
					data[i+2] == 0x49 &&
					data[i+3] == 0x43)
				{
					imgPos = i + 23;
				}
				if (data[i]   == 0xff && data[i+1] == 0xd9)  //end of image
				{
					imgEnd = i+1;
				}
			}
			if ( imgPos == 0 ) // no image data
			{
				Img = null;  
				return false;
			}
			else
			{
				imgLenght = imgEnd - imgPos;
				Img = Image.FromStream( new MemoryStream( data,imgPos,imgLenght ) );
				fs.Close();
				return true;
}

Edited January 3, 2006 by dolimite35