This article describes how VB stores BytesBooleanIntegerLongSingleDoubleStrings Fixed- and Variable-LengthCurrencyDateVariantsArraysand UDTs. I have put in a few points of interest.

These are all marked with BTW by the way. There is no way I can explain the intricacies of pointers here. That is an entire article on its own. But, briefly put, a pointer is a block of memory that stores a value of memory location where some other data exists. In a bit operating system for example, Win 95 and Win NTthe size of the pointer is 32 bits 4 bytes and has a range of 0 to 4,, approx 4 Gigs. In a few years, when memory sizes exceed 4 Gig, we are going to need new bit operating systems.

In little-endian format, a multi-byte value is stored in memory from the lowest byte the "little end" to the highest. In big-endian format, a multi-byte value is stored in memory from the highest byte the "big end" to the lowest. Most operating systems for example, DOS and all versions of Windows so far are designed to run using little-endian format.

A few UNIX systems use big-endian format. The following data types are all pretty simple in how they are stored: Byte, Boolean, Integer, and Long. Let's look at each one individually. A boolean variable is represented by 2 bytes. In actual fact, you could get away with using only 1 bit, so 2 bytes is, in my opinion, overkill.

I think it stems from legacy bit computer architecture. A TRUE in boolean is stored as -1 in other words, all bits are 1. However, it should be noted that any non-zero value is also interpreted as TRUE.

Remember that the bytes occur in little-endian format. An Integer in VB is defined in a most unfortunate fashion. Traditionally, an integer is defined as one "word" of an operating system. So, traditionally, on a bit architecture an integer is 16 bits, on bit OS it is 32 bits, and so forth. But, it seems that somewhere along the line VB's integer got stuck in the stone age and was cast in stone as a bit number. A VB long is stored using 4 bytes 32 bitsand has a range of -2,, to 2,, Because the long is bits, it has become the obvious choice to use when needing to store pointers for Windows a bit OS.

A VB data type that conforms to standard of some sort. All floating point numbers, in VB, are stored as either IEEE bit 4 byte floating-point number for single or as IEEE bit 8 byte floating-point number for double. Consider the decimal number ; this may be represented as 1. The same is true for floating-point numbers stored binary, except that the mantissa is multiplied by 2 raised to the exponent as apposed to 10 raised to the exponent as done in decimal. One more thing to note is that, in the IEEE floating point standard, the mantissa is always considered to have the "point" to occur between the first and second bits.

So, a mantissa of 11 binary is interpreted as 1. Now, the mantissa can always be written as a number between 1 and 2; the exponent just needs to be modified accordingly.

So, this means that a 1 will always occur before the "point," and so, because we know that it must always be there, we don't need to store it. Similarly, the number 1. An IEEE number is recorded as being positive or negative using one bit: In the IEEE format, the exponent is offset by half its maximum possible value.

So, for a bit floating-point number the exponent has an offset ofand similarly a bit number has an offset of Thus, an exponent 6.

Another example is the number 0. A VB single is stored using an IEEE bits floating-point number. An IEEE bit floating-point number consists of from most significant to least significant bit 1 sign bit, 8 bits for the exponent, and 23 bits for the mantissa. For example, consider the number 1. Ignore the fact that we are using little-endian format for the moment.

The final 23 bits are the mantissa, with an implied leading 1, thus giving The final 23 bits are the mantissa, with an implied leading 1, thus givingwhich equals 1. A double variable is stored as an IEEE bits floating-point number. An IEEE bit floating-point number consists of from most significant to least significant bit 1 sign bit, 11 bits for the exponent, and 52 bits for the mantissa.

The storage rules are exactly the same as those for a single variable, except that the exponent has an offset of The storage of strings is best understood by looking at the way strings work in C. In C at its most basic levelthere is no sting data type. There is, however, a character type char. A char is a simple one byte variable that represents a single character. And so, a string in C is simply an array of characters; in other words, a whole bunch of characters strung one after the next in memory.

So, a string can be drawn as follows:. This is a simple 12 character string, but an extra character is needed for the null termination character.

Thus, the number of bytes required in memory is But, as with all things, there is a problem with this. It is the number of possible characters that can be represented by a single byte: Now, 52 of those are taken up by roman characters 26 for upper case and 26 for lower10 for numerical charactersplus all the punctuation colons, commas, and so forththen there are the "modified" roman characters i.

And then, a few more for "reserved characters. So, the next thing that was realised is that two bytes should be used for each character. This gives a possible 65, different characters. While this is mostly true in VB, Windows actually uses UTF so it can encode a lot more characters by using surrogates. Apparently, this is enough for most of the characters of the world's languages. So now, each character is two bytes the original ASCII set is defined by a 0 in the high byte and then the character values in the low byte.

This new representation of strings is known as "wide" characters. So, our string looks like this:. Please note that the dots represent the extra byte per character. Note also that the extra byte occurs AFTER the character because it makes use of little-endian data formatting See " Big- and Little- Endian Data Formats ". DOS 1 through 6 and Windows 3.

WinNT used wide characters but accepted the original ASCII. Nowm let's look at how to store and address strings. To address a stringm one typically has a pointer that points to the first memory location of the string. And obviously, the rest of the string follows on from there. So, we have the following situation for a old ASCII string:. Simultaneously, it was realised that many string operations could be made a lot more efficient if free forex indicator for android length of the string was known.

And so, this new standard was defined:. This was known as HLSTR. Here, a pointer points to a descriptor, which contains both the length of the string and a pointer to the string which is NOT null terminated because this is no longer required.

VB 3 used this style of string storage. This worked well for a while, but it has a HUGE fatal flaw. And so, a new style was defined. In how to buy stocks on bombay stock exchange, the pointer points to the beginning of the string which is null terminated for backward compatibility.

Preceding the first character of the string are 4 bytes which contain the number of characters in the string. This is called a BSTR, and this is what is used by VB 6. Notice how you can pass it to any function that requires a LPWSTR and the function will work properly. If you are wondering what happens if the location of the null termination character and the length descriptor 1 minute binary options indicators reddit match up, well The null terminator is only there for backward compatibility.

How to make money with cannon runescape only slight problem occurs when you pass it to a LPSTR.

In this case, the second byte of the string is interpreted as the null terminator if one is using the ASCII character set. But, this problem seldom rears its head. A fixed length string is stored as a series of bytes, occurring in sequence in memory. The number of bytes required is twice as many as the length of the string. The string is then stored in the bytes, using wide characters. Fixed-length strings are NOT null terminated. Also, fixed-length strings do not utilise a pointer to point to the string.

Variable length strings are stored using BSTR as described above.

It, therefore, consists of a pointer, the string's length, and the null-terminated string. This BSTR is suitable for passing to API functions that utilise wide characters.

The maximum length of a variable-length string is determined by the size of the length descriptor in front of the string, and is limited to 2 billion.

Each time a new value is assigned to a string even if it is the same lengthVB fetches a new block of memory and stores this new memory location in the pointer, and then releases the previously utilised block of memory. This constant acquiring and releasing of memory means that appending characters to a string is slow. Consider the following somewhat stupid piece of VB code:. Each time the loop is executed, VB forex currencies explained a new chunk of memory, changes the pointer, and releases the old chunk.

This extra overhead can have quite an effect on the performance of VB. A much better way of doing this is to do the following:. Notice how incredibly differently fixed- and variable-length strings are stored. To the end user they look the same, but they are very different. This explains why fixed-length strings are such a pain to work with; they are completely different data types. Don't use fixed-length strings unless you feel you have to, or you need the speed. The Currency and Date data types are, in fact, very simply stored, but are just interperated differently.

A Currency variable is simply a bit 8-byte integer, which is scaled by to give a fixed-point number with 15 digits to the left of the decimal point and 4 digits to the right. So the number 5. A Date is stored as an IEEE bit 8-byte floating point number, just like a Double. Digits to the left of the decimal point when converted to decimal are interperated as a date between 1 January and 31 December Currency swaps options and futures to the right of the decimal point indicate time between 0: The date section of the Date data type before the decimal pointis a count of the number of days that have passed since 1 Janoffset by That is, 1 Jan is denoted by a value of ; 2 Jan is denoted ; 31 Dec is 1; 1 Jan isand so on.

The time section of the date after the decimal point is the fraction of a day, expressed as a time. So, an hour is denoted by an additional 4. Basically put, variants have no definite shape. They change their shape depending on what they are storing. The format of a variant is as follows ignoring endian formats:. The variant is 16 bytes large. It has 2 bytes to describe the type of data it is storing, 6 reserved bytes, and 8 bytes to store the data each block represents enforex valencia opiniones byte.

Type Reserved Data And for call option payoff profile reason, the Type, Reserved, and Data descriptors occur in this order in memory, although the data stored within each occurs in little-endian format.

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The type describer takes on a value depending on what the variant contains. The following list is a selection of the more common values. The data descriptor is filled with data starting from the "left" side. For example, when storing a Boolean variable, which is only two bytes big, the "left" most bytes are used; for example:. So when storing a Byte, Boolean, Integer, Long, Single, Double, Currency or Date, the data of value stored is simply placed into the data descriptor. Now, for storing Strings all strings in variants are variable-lengthArrays, UDT, or other data types for example, objectsthe data descriptor simply takes on the value of memory location of the data in other words, the data descriptor acts as a pointer.

Because the data descriptor is essentially a pointer the only the first 4-bytes are used. For example, the String "This is fun! An array in VB is implemented as a "SafeArray. A SafeArray contains 20 bytes of memory, plus 8 bytes per dimension, plus the memory required to store the stock trading company singapore. The safe array can basically be divided into three sections.

The first is the safe array pointer, the second the "base" of the array, and the third the data area of the array. The safe array pointer is a pointer 4 bytes that points to the base of the safe nigerian stock exchange trading platform. The location of this pointer remains fixed at all times; however, the locations of the "base" change each time the array is redimensioned Redim.

So, how much money does a aircraft engineer make example, a VB array defined using the code:. Mosin nagant m91/30 thumbhole stock rgsabound array is stored with the right-most dimension in rgsabound[0] and the left-most dimension in rgsabound[cDim.

The data array is simply a sequence of elements of the array. It should be noted that, for an array of strings or objects, only the pointer is stored in the arrays data sequence in other words, m equals 4 bytes, the size of a pointer. The data is stored in such a way that the first dimension is stored first, then the second, and so on. Pointed to by pvData in Array "Base".

Notice the order of the rgsabound array. The last right-most dimension is the first element in the rgsabound array. Notice the order with which the data is stored in the data area. The first element is 0, 1 then 1, 1 then 0, 2 and finally 1, 2.

How Visual Basic 6 Stores Data

When a VB array is redimensioned using the Redim commandthe array changes as follows although not necessarily in this order:. If you use the Preserve keyword, you can resize only the last array dimension and you can't change the number of dimensions at all. Similarly, when you use Preserve, you can change the size of the array only by changing the upper bound; changing the lower bound causes an error.

A UDT is stored a sequence of consecutive memory blocks, as per the data types used. Often, padding is used between elements. The padding differs from one configuration to another. There doesn't seem to be a distinct pattern to it. The best way to determine whether you have padding anywhere is to us the algorithm given below. String as pointed to by strVar.

To gain access to the "hidden" data in VB and to REALLY play around with variablesyou need a few things that VB doesn't let you do. There are actually ways of working with pointers in VB, but it is a bit of a hack You are going to need the following commands to gain access to pointers: VarPtr, StrPtr, and ObjPtr.

Can't find any documentation on these commands? Well, here's the bad news; Microsoft will all but deny that they exist in Visual Basic. This is because if you start mucking around with them you could break VB quite spectacularly; and, furthermore, the way VB stores data differs from version to version, so the commands will not always act as expected on other versions.

Thus, there is no backward or forward compatibility. But don't let this scare you. VarPtr returns the pointer VB type long to a variable. It points directly to the data for Boolean, byte, integer, long, single, double, currency, and UDTs.

But, for strings, it returns the pointer to the string pointer, and for variants it points to the beginning of the variant. StrPtr returns a pointer to the string data in other words, it is the same as using VarPtr to get the string pointer and the returning the contents of the string pointer.

To complete your arsenal of pointer functions, you'll also need an API function known as CopyMemory. This command copies memory from one location to another.

It is requires the following define statement:. You may also want to take a look at CopyMemoryVlm, MoveMemoryVlm, FillMemoryVlm, and ZeroMemoryVlm if you need bit versions. You'll get a nice "Type Mismatch" error. VB absolutely will not let you pass an array to VarPtr and passing an element just returns the data area. So, how do you ever test the memory storage of an array?

Or for that matter, ever hack it? Well, you wrap it in a UDT and then get the address from that Now, try dimensioning the array only later in code:. You get a pointer in the printout. Follow the pointer if you like and you'll get the "base" of the array. Here is the complete code for doing this:. How can i convert ascii to 4 byte floating if data i have is in little endian format from a serial port. Data is sent in 8bits with COM Port settings MSComm1.

How can i change that 8bit ascii with output of it as to a 4BYTE Floating number like 0. Please Help Output is: Hi there, I use the following code to get infos about the ram area where VB6 stores array data: Have a nice day. Massimo I use the folowing code to get the ram area where VB6 stores array data: I missed to tell you that this method doesn't work with variable length strings and variant arrays, because the size of any single array's element may be different. I ran across this trick someplace online.

All you need to do is pass the array to a function as a Variant, and then unwrap the pointers stored in the Variant to get to the array base. This has the advantage of not having to wrap the array in a UDT in code -- in fact, any array that can be coerced into a Variant can be unwrapped. The code is in this thread: Nice article, very good explanations. Just like to add, about getting array addresses, see this page: Fantastic article, really helped my understanding of how this worked and allowed me to start moving memory around and passing variables to API calls etc with more confidence.

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Variant used only with arrays of variants. A count of the number of dimensions in the array. Size of each element in the array. A pointer to the first data element in the array.

Array is allocated on the stack. Array is statically allocated. Array is embedded in a structure. Array may not be resized or reallocated. Bits reserved for future use. The number of elements in the dimension. The lower bound of the dimension. Data Area Pointed to by pvData in Array "Base".