search hex values in a file

[starface245]

I'm trying to look for a method or function code to look/search for a specific hex value in a file

I'm want to look for this value in a file

0x67452301

Like if I open a hex editor, it shows "67 45 23 01"

I just want to check if those values exist in a file or not, that all...

[hamsterman]

If the file isn't large, you could read it all into a char array (using read()) and the use http://www.cplusplus.com/reference/algorithm/search/ to find what you need.
Another way would be to read one byte. Then compare it to 67. If there's no match, repeat. If there is a match, read another byte and compare it to 45, and so on..

[PanGalactic]

Use Boost regex, passing in a pair of istream_iterators. I'd suggest doing that with std::search, but it requires forward iterators, not input iterators. Boost regex supports searching with input iterators. Though the documentation is a bit ambiguous, I know it can be made to work. I've got code that reads and parses data from std::cin using streambuf_iterators.

http://www.boost.org/doc/libs/release/libs/regex/index.html

[Galik]

Depending on what you want to do with the result you might want to consider the benefits that stream iterators have to offer:

#include <string>
#include <fstream>
#include <iterator>
#include <iostream>
#include <algorithm>

int main()
{
	std::ifstream ifs("input.txt");

	// begin = start of file
	// end = end of file
	std::istream_iterator<char> begin(ifs), end;

	// string to match
	std::string str = "\x67\x45\x23\x01";

	// search file for string
	if(std::search(begin, end, str.begin(), str.end()) != end)
	{
		std::cout << "found" << std::endl;
	}
}

[PanGalactic]

Galik, According to the docs, std::search requires a ForwardIterator, and std::istream_iterator models an InputIterator.

http://www.cplusplus.com/reference/algorithm/search/
http://www.cplusplus.com/reference/std/iterator/istream_iterator/

It compiles but doesn't work on at least one platform I have access to (Solaris + Sun Studio).

That's because it's std::search implementation calls std::distance, which consumes all of the input before actually searching the text.

[Galik]

That's interesting. You're right the iterator types don't match. That's a shame, it works on my Linux implementation. After the search is successful the input stream is only consumed up to (and including) the matched portion. But that evidently can't be relied upon...

[starface245]

Thank you Galik, that wat I was looking for, the iterator type was the key for me.

Thanks all you guys for helping for the inputs and advice as well. Worked out great.

[starface245]

I kinda found a problem, if the string str = "\x0G";

It still displayed found but G isn't part of the hex.

[Galik]

A couple of things. First, my method has a fault as PanGalactic pointed out. It works on some systems but not others, so its not a good idea to use it. Second "\x0G" is not a HEX value. You shouldn't enter something like that into a string literal. I tried it on my system and it did not complain but it is equivalent to using an empty string "". An empty string is always found.

[starface245]

O ok, thanks the explanation. now got the better understanding of it.

[starface245]

I'm having this crazy situation...

I'm using cygwin to compile and run the file, and it works perfectly.

Then I test it again, using QT creator, it builds fine, but when I run the program. It does not seem to work. I check to see if the program actually open the files, and it does, but it does not do the search.

So I'm guess this where PanGalactic pointed out applies?

[Galik]

It could well be. There is no reason that my method should work the same on two different compiler/library implementations.