Get rid of dead code
Dead code means unnecessary, inoperative code that can be removed. Dead code includes functions and sub-programs that are never called, properties that are never read or written, constants and enums that are never referenced. Dead variables are ones that are never read - even if they've been given a value. User-defined types can also be dead, and there may be a lot of extra API declarations. Even whole
files can sometimes be completely unnecessary.
Dead code leads to excessive memory use, slower execucation, larger .exe files, higher maintenance effort and errors. That's why it's important to clean your projects by removal of dead code.Avoid fixed-length Strings
Fixed-length strings generally occupy more memory than variable-length ones. The problem is worse if you have to reserve lots of space for long strings in your fixed-length string variables. If you're planning to migrate to VB.NET, then you have one more reason why not to use fixed-length strings. VB.NET doesn't support
them natively. You get better performance with variable-length strings. Read more about migrating to VB.NETAvoid static variables
Static variables are those that reside in the memory for the whole execution time. The opposite of static variables are dynamic variables. Dynamic variables are procedure-level variables that are created when the procedure is entered, and destroyed when the procedure ends.
How do I know which variables are static or dynamic?
1. Variables declared in the (declarations) section.
2. Local variables declared with the Static keyword.
1. Arrays declared with subscripts in the (declarations) section.
Dim MyArray(1 To 45)
2. Local arrays declared with the Static keyword.
Dynamic Local variables.
1. Arrays declared without subscripts in the (declarations) section.
2. Local arrays declared with the Dim or ReDim keywords.
Local are those variables and arrays that are declared inside a procedure. So why should you avoid static local variables? Static variables are slower and consume memory. It is better to use normal, dynamic local variables. If you really need a static local variable, use a private module- level variable instead. There is a drawback with this, though. You should keep other procedures from using the same variable to avoid unwanted side-effects.Reclaim memory after use
If you are using static variables, it's important to reclaim the memory they occupied when you don't need the variables any more. With dynamic variables memory isn't so much of a problem, because they are destroyed when the procedure ends.
The below table shows how you can reclaim the memory occupied by different variable types. Arrays are discussed below the table.
Type of variable Code to reclaim occupied space
Variable-length String MyString = vbNullString
Variant MyVariant = Empty
Form Unload MyForm
Object Set MyObjectVariable = NothingReclaim memory from arrays
Arrays are often memory-hungry. This applies especially to staticarrays, whose size is fixed for the lifetime of the program. Dynamic arrays are better for memory optimizations, because they can be resized. However, some memory optimization can be applied to both array types. One way to reclaim space occupied by an array is to clear all its elements one by one as shown above. Another way is to use Erase or
Erase frees the memory used by dynamic arrays. With static arrays, however, the effect is somewhat limited. Doing Erase for a static array is the same as clearing all its elements separately. ReDim can be used only for dynamic arrays. You can ReDim a dynamic array to a smaller size. If you just want to reduce the array and
still preserve some data in it, you can use ReDim Preserve, like this:
ReDim Preserve MyArray(SmallerSize)Type your variables
VB's default data type is Variant. All variables that don't have any other type are implicit Variants. Avoid variants when possible. They are slow, and they consume memory. If you use variant instead of, say, integer you waste 14 bytes of
memory. This can be significant in a large project. Integers are much faster than variants. This is true particularly in For..Next loops. Use Option Explicit to force declaration of your variables. This helps you to get rid of unnecessary variants.
Aivosto Project Analyzer can help you to ensure properly typed variables. It can list the implicit Variants and missing Option Explicit statements for you. Typing your variables is a very good habit and a sign of professional development.Memory optimizations with graphics
Graphics may use a lot of memory and also slow your program down. Here are some easy tips to avoid that. Reclaim graphics memory with LoadPicture() and Cls. You can also set the Picture property to Nothing (VB 4.0 and later). Use Image controls instead of PictureBoxes. Use RLE, GIF, JPG, and WMF picture formats instead of BMPs. If
possible, try to reduce the number of colors in your pictures. Load a picture only once. If you need to display one picture in several places, you can just assign it from one control to another with this code:
MyGraph.Picture = OldGraph.icture
Doing this will save the picture only once in your executable file, but you may use it on many controls. Set AutoRedraw = False. If it's True, VB will create an AutoRedraw image that consumes memory.Optimize for speed
Users are often complaining about slow programs. They may have slightly old computers, but usually it is the developer to blame. How to make apps faster?
Some memory optimizations described in the previous chapter contribute to speed optimization too. These are getting rid of dead code and using appropriate variable types instead of Variants. On many occasions, when you minimize memory usage you will also minimize execution time. In some cases, however, the two goals may be
Aivosto VB Watch Profiler is a performance measurement tool that can help you squeeze the most out of your code. It measures the time your code takes to execute - line by line, procedure by procedure. You can make before-after comparisons and check which algorithm is the best one to use. You can also find the bottleneck areas in your project - the areas where you can achieve maximal performance boost with
Now let's see some ways to make faster code.Optimize string handlingCache properties in variables
If you are going to need the value of a property more than once, assign it to a variable. Variables are generally 10 to 20 times faster than properties of the same type. Use For Each..Next
Collections allow you to iterate through them using an integer For (index)..Next loop. However, For Each..Next is often faster. Besides, it's easier to read too!
Check for loops Normally, loops are those parts of a program that take the most time
to execute. The worst thing is several loops nested. You can use Aivosto Project Analyzer to find out where the deepest loops are in your code.Mathematical complexity
You may have heard of mathematical complexity measures like O(n) and O(n2). O(n) means that the execution time of a procedure is proportional to the input size n. O(n2) means it's proportional to the square of the input size. In other words, O(n) is much faster= than O(n2), if n is large. What is n, the input size? It can be anything, including the number of lines in a text file, the dimensions of an array, or the size of binary data. It all depends on what you're programming.
The worst case is denoted by O(2n). This means that execution time rises exponentially when n increases. On the other hand, if execution time rises only logarithmically, like O(log n), you have a fast procedure even for large sets of data.
Very briefly, you calculate mathematical complexity like this.
Code example Complexity
For i = 1 to n
Debug.Print "Hello, world!"
End Sub O(n)
For i = 1 to n
For j = 1 to n
Debug.Print "Hello, world!"
End Sub O(n2)
For i = 1 to n
End Sub O(n3)
Mathematical complexity (and the time to execute) is mostly due to the number of nested loops. With a recursive procedure (procedure that calls itself), the problem isn't that simple, but most of VB procedures are not recursive.Working with objects
Minimize the dots. Each dot consumes some time, and makes the code more difficult to read. You can refer to an object's default property just with the name of the object (without the name of the property!). You can also assign an object to an object variable, like this:
Dim X As SomeObject
Set X = SomeContainer.SomeObject(123)
Now you can refer to X instead of the long alternative. You can use With..End With for the same effect, but beware! There is a caveat. With..End With takes some time to execute, so it's not effective to use it to replace just one or two references to an object's properties. Experiment.Early and late binding
If you know what type an object will be, use that type! Avoid variables declared As Object or As Variant. This is called early binding - VB knows what type to expect at
compile time. The opposite is late binding - the type is known only at run-time. Late binding is much slower. Remember to declare your objects properly!Optimize display speed
Often it's important how fast your application appears to run, even if the the actual speed isn't that high. Some ways to speed up display speed: Set ClipControls property to False. Use Image instead of PictureBox, and Label instead of TextBox, if
possible. Hide controls when setting properties. This prohibits multiple repaints.
Keep a form hidded but loaded if you need to display it fast. The drawback of this method is that it consumes some memory. Use background processing for longer runs. You can achieve background processing with appropriately placed DoEvents. A good place to put DoEvents is inside time-consuming loops. This needs some
consideration, because the user might click some buttons, for example, and your program must know what the user is allowed to do when the background process is running. Set flags like Processing=True and check them in appropriate places.
Use progress indicators. Pre-load data you will need later. For example, you can load the contents of a database table into an array for faster access.
Use Show in Form_Load event.
Simplify your startup form, or use a splash screen. How to write understandable code
Do you like spaghetti? No matter if you do or not, you probably don't
like spaghetti code. It is very common to find poorly designed code that is difficult to understand. But that would also be easy to avoid. After all, it is so
easy to make understandable code. It doesn't really take a lot of time - but it will save a lot in the future.Start writing decent code now!
Making non-spaghetti code is not about writing a few docs after the program is ready. It is a continuous process that starts at the same time you write the first line of code. Think about the reader that will read the code next year. Will he or she understand the code that has no indentation, meaningless variable names, jumps from place to place, and no comments? Besides, that person might be you!
Aivosto VB Friend is a tool that beautifies your code while you write it. It adds proper indentation and whitespace, and splits complex structures to multiple lines. You can customize it to fits your own personal coding style.Naming conventions
Use descriptive module, procedure, variable, constant and control names. Longer names tend to be more descriptive. Use constants instead of numeric values and string literals. Like this:
Global Const APPNAME = "My Fancy Program v1.0" Global
Const MAX_SIZE = 32767
Use prefixes for standard naming. There are numerous naming conventions to choose from. They usually use things like "g" for Global, "i" for Integer, so giAge would be a global integer for storing someone's age. Search the web for naming standards and pick your favorite one! Below are a few good starting points.
Comment every procedure, module and the interface to them. A good practice is to put a few comments just after the procedure name, like this:
Function FileAge(ByVal Filename As String) As Long
' Detects how old the file Filename is.
' Returns the age of the file in days,
' -1 in the case of an error.
' Includes error handling.Document the structure of your project - which module does what, and which modules call which one.Things to avoid
The usual advice: Don't use GoTo! There is nothing you can't do with If and Do..Loop. The only exception is On Error GoTo. The same advice goes for GoSub too, except that you won't need GoSub at all. Split complex procedures Overly long and complex procedures are hard to understand. They are error-prone. One particular sign of a complex procedure is the amount of nested conditionals (if, do..loop, select case).Use ByVal (or ByRef) parameters
By default, all parameters to a VB procedure are passed by reference. Unfortunately, this is not the preferred way in most cases. When you pass by value, you'll get saved from subtle bugs. Passing by value (ByVal): The procedure gets a copy of the actual value of the argument.
Passing by reference (ByRef): The procedure gets access to the argument's actual memory address. When a ByRef parameter is used, the value of the passed argument can
be permanently changed by the procedure. Although sometimes you want
to use this effect, most of the time it is not what you want.
Consider, for example, the following piece of code:
Function MultiplyByTwo(x As Integer) As Integer
x = x * 2
MultiplyByTwo = x
MyNumber = 7
How much is MyNumber after a call to MultiplyByTwo? It's 14, although one would easily think it's still 7! This happens because MultiplyByTwo doubles the value of parameter x before returning it back, and the change reflects in MyNumber. In
fact, passing parameters by reference means that MyNumber and x are
the same variable! The solution is easy. Pass the parameter by value using ByVal, like
Function MultiplyByTwo(ByVal x As Integer) As Integer
Now, even if MultiplyByTwo changes the value of x, it will never change the value of MyNumber in the calling procedure. If you really want to use by reference passing, use it explicitly like this:
Function MultiplyByTwo(ByRef x As Integer) As Integer
Now, why would you want to pass by reference? Sometimes you get better performance that way. That's because the contents of the variable are not copied to the sub-procedure. The extra performance comes with a cost though, so use this optimization with care.Use Private
Whenever possible, use the keyword Private. This will make your procedures and variables accessible inside the same module only. The advantage is increased modularity in your code.
Private MyVariable As Integer
Private Sub MyProcedure()
Knowing which thing should be Private and which one Public is difficult, especially if that wasn't taken care of when the original code was written. If a thing is Public when it shouldn't, it's called the excess scope problem. Fortunately, this
problem is easy for an automated code analysis to solve.How to write robust codeUse proper error handling
VB apps crash easily, with messages like "Invalid function call" and "Overflow".
A quick and dirty way to prevent crashes is to use On Error Resume Next. Put it in every procedure, and your app completely ignores most errors. The user never knows what went wrong if she never sees one error message.
A more sophisticated solution is to build real error handlers. If an error occurs, display a meaningful error message and give the user the ability to ignore the error, retry, or abort the program. For your own purposes, build and show enough information so that the user may report any bugs to you to fix. Put this in every procedure, and you have a robust program.
Add error handling easily Work, work, and work! That's what proper error handling requires -How to develop more efficiently
Reuse, reuse, reuse! Reusability is the magic word of programming today. In VB, you can reuse procedures, code modules, or class modules. Reuse greatly
reduces the time to develop a program. You can achieve reusability if you program in an object oriented language creating reusable classes. Although VB isn't a strictly
object oriented language, it has a class mechanism called class modules (.cls). VB can also create ActiveX controls - quite a powerful mechanism for reuse.Debugging executables
It is usually not enough that an application runs on your own computer, or your colleague's one. It must run on the customers'computers too. Debugging is tough when you have to debug executable files - and that's the way to do it if you have to debug on someone else's computer. That may also be the case when you use ocx or dll files.