A beginner’s guide to writing a custom stream buffer std:: They support options for lax parsing, lossy conversions, pretty-printing, and base64 encoding. As a writing note, if you’re finding yourself doing that too often, then you may streambuf to use a string representation of your data, custom can simplify this kind of random access operation. To keep the implementation simple, we’ll mandate that the following invariants hold and are set up by the constructor: This is because we don’t have to worry about a put-back area like we did for input buffers. You’ll find that the need to override uflow typically arises in stream buffers that don’t use a writeable array for intermediate storage.

A stream buffer is the vegetated land adjacent to a streambank. It should be trivial to plumb in support custom locales if need be. Instead it is one byte less. The first line of the function looks to see if the buffer is exhausted. I’ll describe what the new functions uflow , pbackfail and showmanyc do when we get around to defining them.

FILE buffers to integrate with C code For our first example, let’s look at the case where ccustom might have some legacy C code to contend with.

writing custom streambuf

Now a buffer can’t do this if its end back pointer is equal to its end get pointer i. Note that we didn’t really have to use an internal buffer for this example, we could have simply processed characters one at a time and immediately sent them to the sink in overflow in which case the default implementation of sync would have been sufficient, too.

This example is a little different from the previous one in that we don’t really need a buffer. Again, it is typically the case that eback and egptr won’t change during the life-time of the streambuf. However, implementing a dual-purpose streambuf is a fair bit trickier, so I won’t be considering it in this post. I’ll describe what the new functions uflowpbackfail and showmanyc do when we get around to defining them.

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In the case where the buffer is exhausted, we must re- fill it before returning the first new character.

You are commenting using your Twitter account. The default implementation in std:: The correct form of read-only std:: I quiver in anticipation. Stack Overflow works best with JavaScript enabled.

Custom streambuf class

For an input stream buffer, we have 3 different pointers to contend with, though they have a roughly analogous purpose. If you were new to stream buffers before you read this post, I hope you feel a little more comfortable with them now.

writing custom streambuf

How can we provide it with such a stream? Instead, take a std:: However, there are a few issues with the code above that make it less modern and type safe than it could be. But I do not need all the info.

writing custom streambuf

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For B You need to create your own streambuf and connect your ostream to that buffer constructor argument.

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Calling setg is how we tell the streambuf about any updates to the positions of ebackgptr and egptr. The code for all the examples is available at the end. Another example, benchmarking both the library and msgpack pecl extension:. Leave a Reply Cancel reply Enter your comment here Yeah, OK – not those stream buffers.

Custom streambuf class | Coding Forums

Streambut perhaps save that for another post, but if you’d like to look at how to do that yourself, then look up the std:: In C, it is true. Typically, pbase and epptr won’t change at all; it will only be pptr that changes as the buffer is used.

Now, we’ll use an std:: All the implementations were pretty basic, but a lot more is possible. The implementation of sync is trivial: This is because we don’t have to worry about a put-back area like we wriying for input buffers.

However, there is some extra functionality that we might like to add. In this example, we’ll look at the situation where you already have a read-only array of bytes in memory and you’d like to wrap it in an std::