I inherited this old TurboBasic code base, and I am converting it to something more modern.
Can you explain how in this code snippet Wind can be both a variable and an array?
Dim Wind(1:3,2:3)
Sub WindFunction
Shared Wind()
local var
Erase Wind
Wind = 123
var = Wind
Wind(1,2) = 567
End Sub
The wikipedia page on Turbo Basic suggests that it is one of the dialects where
A ... double
A$ ... string
A(...) ... array of double
are treated as totally separate variables, so in your case you have
Wind(...) ... an array of double
Wind ... a double
These dialects treat most variables' types just by their name. Only arrays need to be declared. Sometimes even arrays can be addressed without declaration, they are then assumed to be an array with one dimension and a size of 10.
Some more links can be found here on SO (oh, just saw it's by you, too *g*):
https://stackoverflow.com/questions/4147605/learning-turbobasic
Related
I recently looked up an example of simple Lua oop principles and modified it slightly, as seen below.
What I find trouble comprehending is the connection between elf.name and hobbit.name. Why is it that when I change the value of either, that it affects the other? I am aware that I could have set elf.name as local inside the function, but it wouldn't have had the same effect.
In contrast, changing the value of another.name has no effect on the other two. Is there a lasting connection between elf.name and hobbit.name? I thought they were treated as separate objects.
Thanks.
;^)
Zalokin
elf = {}
elf.name = "Frodo"
another = {}
function Character()
return elf
end
local hobbit = Character()
print ("elf.name set to Frodo")
print("hobbit.name - "..hobbit.name)
print("elf.name - "..elf.name.."\
")
hobbit.name = "Charlie"
print ("hobbit.name set to Charlie")
print("hobbit.name - "..hobbit.name)
print("elf.name - "..elf.name.."\
")
another.name = "Gary"
print ("hobbit.name set to Charlie and another.name set to Gary")
print("hobbit.name - "..hobbit.name)
print("elf.name - "..elf.name)
print("another.name - "..another.name.."\
")
Result: -
>>>>elf.name set to Frodo
>>>>hobbit.name - Frodo
>>>>elf.name - Frodo
>>>>
>>>>hobbit.name set to Charlie
>>>>hobbit.name - Charlie
>>>>elf.name - Charlie
>>>>
>>>>hobbit.name set to Charlie and another.name set to Gary
>>>>hobbit.name - Charlie
>>>>elf.name - Charlie
>>>>another.name - Gary
Any use of {}, is known as a table constructor. It creates a whole new table. When you do elf.name = "Frodo", you're modifying the table that elf points to. In your code, elf and another are initialized separately. On the other hand, hobbit is indirectly given a reference to elf. In other words, elf and hobbit are references to the same table.
function Character()
return elf
end
local hobbit = Character()
That's what you are wrong at. I belive lua is pass-by-reference. This way, your code doesn't work. Also, Hobbit shouldn't be instance of Elf - if Lua is pass-by-reference its natural that instances will share data. Also, at top elf's name is Frodo. I recommend you to remove it. All you need to do is do this like you did with another object.
EDIT: Lua IS pass-by-reference but only on tables and objects.
Quoting Lua 5.1 Reference Manual:
There are eight basic types in Lua: nil, boolean, number, string,
function, userdata, thread, and table. ....
Tables, functions, threads, and (full) userdata values are objects: variables do not actually contain these values, only
references to them. Assignment, parameter passing, and function
returns always manipulate references to such values; these operations
do not imply any kind of copy.
I have written a version control module. The AutoExec macro launches it whenever I, or one of the other maintainers log in. It looks for database objects that have been created or modified since the previous update, and then adds an entry to the Versions table and then opens the table (filtered to the last record) so I can type in a summary of the changes I performed.
It is working great for Tables, Queries, Forms, Macros, etc but I cannot get it to work correctly for modules.
I have found two different properties that suggest a Last Modified date ...
CurrentDB.Containers("Modules").Documents("MyModule").Properties("LastUpdated").Value
CurrentProject.AllModules("MyModule").DateModified
The first one (CurrentDB) always shows "LastUpdated" as the Date it was created, unless you modify the description of the module or something in the interface. This tells me that this property is purely for the container object - not what's in it.
The second one works a lot better. It accurately shows the date when I modify and compile/save the module. The only problem is that when you save or compile a module, it saves / compiles ALL the modules again, and therefore sets the DateModified field to the same date across the board. It kind of defeats the purpose of having the DateModified property on the individual modules doesn't it?
So my next course of action is going to a bit more drastic. I am thinking I will need to maintain a list of all the modules, and count the lines of code in each module using VBA Extensions. Then, if the lines of code differs from what the list has recorded - then I know that the module has been modified - I just won't know when, other than "since the last time I checked"
Does anyone have a better approach? I'd rather not do my next course of action because I can see it noticeably affecting database performance (in the bad kind of way)
Here's a simpler suggestion:
Calculate the MD5 hash for each module.
Store it in the Versions table.
Recalculate it for each module during the AutoExec and compare it to the one in the Versions table. If it's different, you can assume it has been changed (while MD5 is bad for security, it's still solid for integrity).
To get the text from a module using VBE Extensibility, you can do
Dim oMod As CodeModule
Dim strMod As String
Set oMod = VBE.ActiveVBProject.VBComponents(1).CodeModule
strMod = oMod.Lines(1, oMod.CountOfLines)
And then you can use the following modified MD5 hash function from this answer as below, you can take the hash of each module to store it, then compare it in your AutoExec.
Public Function StringToMD5Hex(s As String) As String
Dim enc
Dim bytes() As Byte
Dim outstr As String
Dim pos As Integer
Set enc = CreateObject("System.Security.Cryptography.MD5CryptoServiceProvider")
'Convert the string to a byte array and hash it
bytes = StrConv(s, vbFromUnicode)
bytes = enc.ComputeHash_2((bytes))
'Convert the byte array to a hex string
For pos = 0 To UBound(bytes)
outstr = outstr & LCase(Right("0" & Hex(bytes(pos)), 2))
Next
StringToMD5Hex = outstr
Set enc = Nothing
End Function
You can't know when a module was modified. The VBIDE API doesn't even tell you whether a module was modified, so you have to figure that out yourself.
The VBIDE API makes it excruciatingly painful - as you've noticed.
Rubberduck doesn't deal with host-specific components yet (e.g. tables, queries, etc.), but its parser does a pretty good job at telling whether a module was modified since the last parse.
"Modified since last time I checked" is really all you need to know. You can't rely on line counts though, because this:
Option Explicit
Sub DoSomething
'todo: implement
End Sub
Would be the same as this:
Option Explicit
Sub DoSomething
DoSomethingElse 42
End Sub
And obviously you'd want that change to be picked up and tracked. Comparing every character on every single line of code would work, but there's a much faster way.
The general idea is to grab a CodeModule's contents, hash it, and then compare against the previous content hash - if anything was modified, we're looking at a "dirty" module. It's C#, and I don't know if there's a COM library that can readily hash a string from VBA, but worst-case you could compile a little utility DLL in .NET that exposes a COM-visible function that takes a String and returns a hash for it, shouldn't be too complicated.
Here's the relevant code from Rubberduck.VBEditor.SafeComWrappers.VBA.CodeModule, if it's any help:
private string _previousContentHash;
public string ContentHash()
{
using (var hash = new SHA256Managed())
using (var stream = Content().ToStream())
{
return _previousContentHash = new string(Encoding.Unicode.GetChars(hash.ComputeHash(stream)));
}
}
public string Content()
{
return Target.CountOfLines == 0 ? string.Empty : GetLines(1, CountOfLines);
}
public string GetLines(Selection selection)
{
return GetLines(selection.StartLine, selection.LineCount);
}
public string GetLines(int startLine, int count)
{
return Target.get_Lines(startLine, count);
}
Here Target is a Microsoft.Vbe.Interop.CodeModule object - if you're in VBA land then that's simply a CodeModule, from the VBA Extensibility library; something like this:
Public Function IsModified(ByVal target As CodeModule, ByVal previousHash As String) As Boolean
Dim content As String
If target.CountOfLines = 0 Then
content = vbNullString
Else
content = target.GetLines(1, target.CountOfLines)
End If
Dim hash As String
hash = MyHashingLibrary.MyHashingFunction(content)
IsModified = (hash <> previousHash)
End Function
So yeah, your "drastic" solution is pretty much the only reliable way to go about it. Few things to keep in mind:
"Keeping a list of all modules" will work, but if you only store module names, and a module was renamed, your cache is stale and you need a way to invalidate it.
If you store the ObjPtr of each module object rather than their names, I'm not sure if it's reliable in VBA, but I can tell you that through COM interop, a COM object's hashcode isn't going to be consistently consistent between calls - so you'll have a stale cache and a way to invalidate it, that way too. Possibly not an issue with a 100% VBA solution though.
I'd go with a Dictionary that stores the modules' object pointer as a key, and their content hash as a value.
That said as the administrator of the Rubberduck project, I'd much rather see you join us and help us integrate full-featured source control (i.e. with host-specific features) directly into the VBE =)
I thought I would add the final code I came up with for a hash / checksum generation module, since that was really the piece I was missing. Credit to the #BlackHawk answer for filling in the gap by showing that you can late bind .NET classes - that's going to open up a lot of possibilities for me now.
I have finished writing my Version checker. There were a few caveats that I encountered that made it hard to rely on the LastUpdated date.
Resizing the columns in a Table or Query changed the LastUpdated date.
Compiling any Module compiled all modules, thus updated all module's LastUpdated date (as was already pointed out)
Adding a filter to a form in View mode causes the form's Filter field to be updated,which in turn updates the LastUpdated date.
When using SaveAsText on a Form or Report, changing a printer or display driver can affect the PrtDevMode encodings, so it is necessary to strip them out before calculating a checksum
For Tables I built a string that was a concatenation of the table name, all field names with their size and data types. I then computed the hash on those.
For Queries I simply computed the hash on the SQL.
For Modules, Macros, Forms, and Reports I used the Application.SaveAsText to save it to a temporary file. I then read that file in to a string and computed a hash on it. For Forms and Reports I didn't start adding to the string until the "Begin" line passed.
Seems to be working now and I haven't come across any situations where it would prompt for a version revision when something wasn't actually changed.
For calculating a checksum or hash, I built a Class Module named CryptoHash. Here is the full source below. I optimized the Bytes Array to Hex String conversion to be quicker.
Option Compare Database
Option Explicit
Private objProvider As Object ' Late Bound object variable for MD5 Provider
Private objEncoder As Object ' Late Bound object variable for Text Encoder
Private strArrHex(255) As String ' Hexadecimal lookup table array
Public Enum hashServiceProviders
MD5
SHA1
SHA256
SHA384
SHA512
End Enum
Private Sub Class_Initialize()
Const C_HEX = "0123456789ABCDEF"
Dim intIdx As Integer ' Our Array Index Iteration variable
' Instantiate our two .NET class objects
Set objEncoder = CreateObject("System.Text.UTF8Encoding")
Set objProvider = CreateObject("System.Security.Cryptography.MD5CryptoServiceProvider")
' Initialize our Lookup Table (array)
For intIdx = 0 To 255
' A byte is represented within two hexadecimal digits.
' When divided by 16, the whole number is the first hex character
' the remainder is the second hex character
' Populate our Lookup table (array)
strArrHex(intIdx) = Mid(C_HEX, (intIdx \ 16) + 1, 1) & Mid(C_HEX, (intIdx Mod 16) + 1, 1)
Next
End Sub
Private Sub Class_Terminate()
' Explicity remove the references to our objects so Access can free memory
Set objProvider = Nothing
Set objEncoder = Nothing
End Sub
Public Property Let Provider(NewProvider As hashServiceProviders)
' Switch our Cryptographic hash provider
Select Case NewProvider
Case MD5:
Set objProvider = CreateObject("System.Security.Cryptography.MD5CryptoServiceProvider")
Case SHA1:
Set objProvider = CreateObject("System.Security.Cryptography.SHA1CryptoServiceProvider")
Case SHA256:
Set objProvider = CreateObject("System.Security.Cryptography.SHA256Managed")
Case SHA384:
Set objProvider = CreateObject("System.Security.Cryptography.SHA384Managed")
Case SHA512:
Set objProvider = CreateObject("System.Security.Cryptography.SHA512Managed")
Case Else:
Err.Raise vbObjectError + 2029, "CryptoHash::Provider", "Invalid Provider Specified"
End Select
End Property
' Converts an array of bytes into a hexadecimal string
Private Function Hash_BytesToHex(bytArr() As Byte) As String
Dim lngArrayUBound As Long ' The Upper Bound limit of our byte array
Dim intIdx As Long ' Our Array Index Iteration variable
' Not sure if VBA re-evaluates the loop terminator with every iteration or not
' When speed matters, I usually put it in its own variable just to be safe
lngArrayUBound = UBound(bytArr)
' For each element in our byte array, add a character to the return value
For intIdx = 0 To lngArrayUBound
Hash_BytesToHex = Hash_BytesToHex & strArrHex(bytArr(intIdx))
Next
End Function
' Computes a Hash on the supplied string
Public Function Compute(SourceString As String) As String
Dim BytArrData() As Byte ' Byte Array produced from our SourceString
Dim BytArrHash() As Byte ' Byte Array returned from our MD5 Provider
' Note:
' Because some languages (including VBA) do not support method overloading,
' the COM system uses "name mangling" in order to allow the proper method
' to be called. This name mangling appends a number at the end of the function.
' You can check the MSDN documentation to see how many overloaded variations exist
' Convert our Source String into an array of bytes.
BytArrData = objEncoder.GetBytes_4(SourceString)
' Compute the MD5 hash and store in an array of bytes
BytArrHash = objProvider.ComputeHash_2(BytArrData)
' Convert our Bytes into a hexadecimal representation
Compute = Hash_BytesToHex(BytArrHash)
' Free up our dynamic array memory
Erase BytArrData
Erase BytArrHash
End Function
I can currently use the readline and read function to read a line from the file and store the characters in variables governed by the size of the variable im putting them into for example if the first line of the file was
hello,world
and I wanted to store the two words in different variables I would do something along the lines of
file in_file : text open READ_MODE is "hello_world.csv";
variable in_line : line;
variable first_word : string(1to5);
variable second_word : string(1to5);
begin
readline(infile,inline);
read(inline,first_word);
read(inline,second_word);
however that is dependent upon the size of the elements I want to be able to generically read the first element before the comma and assign that to a variable then look for the next element until the next comma and store that in a different variable if that makes sense.
Many Thanks
The open source VUnit test framework has a standalone string operations package containing a split function
impure function split (
constant s : string;
constant sep : string;
constant max_split : integer := -1)
return lines_t;
that you can use to split a string (s) into its parts which are separated by sep. For example
parts := split("hello,world",",");
parts is a vector of elements of type line so parts[0].all would in this case equal hello. Have a look at the testbench for the package and look for the "Test split" test case to see the details on how the function handles various normal inputs and corner cases.
Since we use the line type rather than string we don't have to know the length of individual elements.
I'm one of the authors for VUnit.
I was wondering whether a container with values such as ["abc", 50, myDate, myRealNumber] can be converted to "abc","50","1/1/1900","-50.34" using a single function.
The con2Str global function fails if the input type is anything other than str.
I tried creating my own version of con2str function to use an "anyType" instead of str, but it fails because anyType cannot be assigned a different type after the first assignment.
If such a function exists (it does not), it would have to deal with strings containing quotes etc.
This is all handled in class CommaIo method writeExp.
But it writes to a file of cause.
Regarding your problem with anytype you could use the class SysAnyType which wraps your value in another object so that multiple assignments are possible.
I'm trying to write a subroutine in access 2003 that removes all quote characters from strings in an array. The subroutine removes the quotes successfully in the routine itself, but not when the program returns to the passing function. I'm very confused, as it is done ByRef.
How it is called:
Call removeQuotes(wbs_numbers())
and the subroutine itself:
'goes through a string array and removes quotes from each element in the array'
Sub removeQuotes(ByRef string_array() As String)
For Each element In string_array()
'chr(34) is quotation character. visual basic does not have escape characters.'
element = Replace$(element, Chr(34), "")
Next
End Sub
Can someone please explain what I am doing wrong? I would love you forever!
Your array may be by reference, but element isn't. Iterate by index, and set the string back into the array once you've manipulated it.
You are creating new variable "element" and do not store it back in string_array, so it is not changing.
My VB is a little rusty but a quick google search turned up something like this:
Dim i As Integer
For i = LBound(string_array) To UBound(string_array)
string_array(i) = Replace$(string_array(i), Chr(34), "")
Next