vbFast - make vb create strings AT LEAST 150 TIMES faster!
This tutorial shows how to dynamicly create Visual Basic strings up to 150 times faster by calling the OLE Automation library directly. Please vote or leave a comment.
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<html> <head> <meta http-equiv="Content-Language" content="en-us"> <meta name="GENERATOR" content="Microsoft FrontPage 5.0"> <meta name="ProgId" content="FrontPage.Editor.Document"> <meta http-equiv="Content-Type" content="text/html; charset=windows-1252"> <title>Visual Basic vs</title> </head> <body> <p><font face="Verdana" size="2"><b>Visual Basic vs. C++</b></font></p> <p><font face="Verdana" size="2">Visual Basic stores it's strings in a type referred to in C++ as a BSTR. This type is completely different from the C char type, as a BSTR doesn't necessarily terminate with a null, and it has a different header. The C char is stored as an array of bytes, terminating at a null byte or character 0x0. Unlike C or C++, when you create a string in VB it is automatically filled with data. </font></p> <p><font face="Verdana" size="2"><b>The SLOW way - Visual Basic's String creation<br> </b>When you dynamically create a string in Visual Basic, there are only two methods that VB supports. These are:<br> 1. Using the String function<br> <u>Example:<br> </u></font><font size="2" face="Courier New"> <font color="#000080">Dim</font> strData <font color="#000080">As String </font><font color="#008000">'our string variable</font><br> <font color="#000080">Open</font> "test.bin" <font color="#000080">For Binary Access Read As</font> #1 <font color="#008000">'open a file</font><br> strData = String(LOF(1), 0) <font color="#008000">'create a buffer</font><br> <font color="#000080">Get</font> #1, , strData <font color="#008000">'read data into the buffer</font><br> <font color="#000080">Close</font> #1 <font color="#008000">'close the file</font><br> </font><font face="Verdana" size="2"> The String function takes two parameters, the length of the string and the character to fill the string with.</font></p> <p><font face="Verdana" size="2">2. Using the Space function<br> This is much like using the String function, except it automatically fills the string with spaces.</font></p> <p><font face="Verdana" size="2">Now, for the example above all we want is an empty storage space to fill with data. But VB doesn't do this. In both instances, VB fills the string with data, which can take a lot of time. This is where the API optimization comes into play.</font></p> <p> </p> <p><font face="Verdana" size="2"><b>The FAST way - the OLE Automation library<br> </b>The OLE Automation library provides support, not only for the BSTR type but also for all variable-related operations. To increase the speed of the string creation, we want to tell the OLE Automation library to create a region of memory that we can access - without filling it with data. To do this we will use two functions, RtlMoveMemory in the windows kernel and SysAllocStringByteLen is the OLE Automation library. The declarations are below.</font></p> <p><font face="Courier New" size="2"><font color="#000080">Declare Sub</font> RtlMoveMemory <font color="#000080">Lib</font> "kernel32" (dst<font color="#000080"> As Any</font>, src<font color="#000080"> As Any</font>, <font color="#000080"> ByVal</font> nBytes&)<br> <font color="#000080">Declare Sub</font> SysAllocStringByteLen& <font color="#000080">Lib</font> "oleaut32" (<font color="#000080">ByVal</font> olestr&, <font color="#000080">ByVal</font> BLen&)</font></p> <p><font face="Verdana" size="2">The RltMoveMemory function copies nBytes bytes from the src address to the dst address. The SysAllocStringByteLen allocates BLen of storage space for a BSTR, or in this case a Visual Basic String. In reality, the Visual Basic String is nothing more than a pointer, or a reference to an address in memory that can be used to store the data. With this in mind, we can create out own string allocation function, as shown below.</font></p> <p><font face="Courier New" size="2"><font color="#000080">Public Function </font>AllocString(ByVal lSize <font color="#000080">As Long</font>) <font color="#000080">As String</font><br> RtlMoveMemory <font color="#000080">ByVal</font> <font color="#000080">VarPtr</font>(AllocString_ADVANCED), SysAllocStringByteLen(0&, lSize + lSize), 4&<br> <font color="#000080">End Function</font><br> <br> </font><font face="Verdana" size="2">This may look a bit complicated at first but it is really relatively simple. The function allocates the space and then copies the 4 byte pointer from this space to the string returned by the function. If we were to expand the function a little it would look like this:</font></p> <p><font face="Courier New" size="2"><font color="#000080">Public Function </font>AllocString(ByVal lSize <font color="#000080">As Long</font>) <font color="#000080">As String</font><br> <font color="#000080">Dim</font> lPtr <font color="#000080">As Long </font><font color="#008000">'the address of the allocated memory</font><br> <font color="#000080">Dim</font> lRetPtr<font color="#000080"> As Long </font><font color="#008000">'the pointer to the return variable<br> </font><font color="#000080">Dim</font> sBuffer <font color="#000080">As String </font><font color="#008000">'the variable to return</font><br> lRetPtr<font color="#000080"> = VarPtr</font>(sBuffer) <font color="#008000">'the pointer to the string buffer</font><br> lPtr = SysAllocStringByteLen(0&, lSize + lSize) <font color="#008000">'allocate the memory and get it's pointer</font><br> RtlMoveMemory <font color="#000080">ByVal</font> lRetPtr, lPtr, 4& '<font color="#008000">copy the pointer address</font><br> AllocString = sBuffer <font color="#008000">'return the string with the modified pointer</font><br> <font color="#000080">End Function</font><br> </font></p> <p><font face="Verdana" size="2">It really is not that difficult, and it makes a HUGE speed increase. This article comes with the above function and a benchmark to show the dramatic speed difference. Please leave a comment or vote!</font></p> </body> </html>
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