Very Useful C++ Stream Class

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Introduction

Over the years of Windows programming, I have quite often needed a MemoryStream class to handle various text and binary data streaming tasks. I have also needed to implement my own IStream interface, which of course must be backed by a MemoryStream. So I wrote the CStream class provided in this article. Since then, I have used this class in almost every project I have done. Often, I find I need to build strings a bit at a time. CStream makes a perfect StringBuilder class. You'll never need to worry about memory allocation, no matter how large the stream grows because CStream allocates new memory as needed.

Overview

The key feature of CStream is that it takes care of growing the internal buffer as needed. And the key to high performance is using VirtualAlloc. This is a very fast memory allocation function created just for this sort of situation where memory is reallocated often.

CStream implements the COM IUnknown and IStream interfaces*. This means you can use it wherever an IStream is needed. In addition to the IStream interface, there are many helper/access methods which give access to the internal buffer for example.

CStream is implemented in Stream.h and Stream.cpp.

* The IStream interface is not fully implemented - only the most commonly used methods.

Using CStream

Suppose you need a StringBuilder because you need to build up a string a bit at a time. Here's the code:

CStream strm;

strm << "This is ";
strm << "an example ";
strm << "of a multibyte ";
strm << "string builder ";
strm << "using CStream";
// NULL terminate
strm << char(0);

// now get the pointer to the stream buffer, casting it to the
correct type

PSTR pszString = (PTSTR) strm.GetBuf();

You only need to declare the CStream and begin writing to it. You can use the overloaded << operator or CStream::Write. Be sure to write a final NULL terminator before calling CStream::GetBuf. GetBuf returns the internal buffer as a BYTE* which must be cast to our desired type in this case.

Binary data streaming is accomplished using CStream::Write, as shown in the following example:

CStream strm;
char szFilename[300];
GetModuleFileName( NULL, szFilename, sizeof(szFilename) );

CFile file( szFilename, CFile::modeRead );

BYTE buf[500];
UINT nRead;

while( nRead = file.Read( buf, sizeof(buf) ) )
{
   strm.Write( buf, nRead, NULL );
}

Useful Methods

Besides GetBuf, CStream also has these helper methods:

• GetByte: Returns the Byte at the current position, with the option to advance the current position.
• GetCurPos: Returns the current internal position.
• GetEndPos: Returns the current end position. This is not the current total allocated size, but rather the highest place in the buffer which has been written to.
• SetEndPos: Sets the current end position, resizing the stream if necessary.
• SeekToBegin: Sets the internal position to the beginning of the stream.
• SeekToEnd: Sets the internal position to the end of the stream.
• Seek: Sets the internal position to the indicated position in the stream.
• Reset: Resets the stream, optionally setting the size.

Conclusion

Text and data streaming are common things to do in programming. This stream class fills the need quite nicely. I hope you find it to be as useful as I have.

History

• 8^th October, 2009: Initial version