How can I find a certain sequence of characters in a string?

[systemdot96]

Hi all, I have a decent amount of knowledge of C++ and I'm working on creating a simple blockchain (not cryptocurrency, just blockchain) implementation in C++, I want to find a certain sequence of characters, in this case "000" in a string to check if a hash (stored as a string) is valid. However, I've tried using the member functions of std::string to do that, but it only looks to see if there is a 0 anywhere in the string, but I want it to look and see if a string has a sequence of characters. Any help on this issue would be appreciated! :D

Heres a code snippet of my current attempt at trying to do this:

std::string output; // pretend theres a sha256 hash here

if(output.find("000")) // Heres where it checks if there is 000 present
		{
			std::cout << "Hash is valid - Block confirmed" << std::endl;
			validHash = true;
			return true;
		}

[tpb]

Having a decent knowledge of a programming language includes being able to look up how a function actually works instead of making assumptions about it. std::string::find doesn't return a bool. It returns a size_t (more specifically, a std::string::size_type) indicating where in the string the target was found. If the target is not found in the string, it returns std::string::npos (generally equal to size_t(-1), i.e., the highest size_t value). So you need to say:

if (output.find("000") != std::string::npos)

[closed account 3UohqMoL]

@tpb it now returns streampos

[tpb]

@Wasp, that seems unlikely to me. What is your reference?

[closed account 3UohqMoL]

@tpb sorry it returns streampos when used with files.
I heard it from iso cpp.

[systemdot96]

Well, I did a return true statement as this is part of a class and the code snippet I provided is part of a boolean function, I apologize if im being ignorant and a little stupid about all this, this is my first time on this forum and I'm still learning the ins and outs of C++

If you want, I can provide the full class code I'm working with to give more insight into my issue

[tpb]

Nobody's saying you can't return true. You can return whatever you want from your own functions. The point is that std::string::find doesn't return a boolean, but you are using it as if it did. It returns a size_t (an unsigned integer type). You need to rewrite your code snippet like this:

std::string output; // pretend theres a sha256 hash here

if(output.find("000") != std::string::npos)
{
	std::cout << "Hash is valid - Block confirmed" << std::endl;
	validHash = true;
	return true;
}

[systemdot96]

Ah I see now, now my code is working like a charm :D

Thanks for your help man! Next time ill just look at the documentation a little bit more lmao

[Kity]

I see it now.