I have a few const arrays of the same base type but different sizes, and I need to point to them in the const records. The code below compiles successfully, but finishes with error.
Return Multiple Values from a Delphi Function. Search the site GO. Computer Science. Delphi Programming Basics. Function WhereAmI(const townName: string): TLatitudeLongitude. Understanding and Implementing Array Data Types in Delphi. • In Delphi, the following syntax is used to declare an array of. Const arr5: array[0.4] of integer = (-200,-100,0,100,200). Arrays in Delphi. I would like to declare a multidimension array of constant values. I want to do something like this: const A: Array[1.2,1.2] of real = ( 1.0,2.0, 3.0,4.0); It will work for a one dimensional array but it does not for multidimensional arrays.
In my code I need to access data from the cOffsetsA/B arrays having a pointer to the record. I tried to do it like this:
and this causes error - 'Access violation .. read of address 000000..'
Can anybody explain is wrong here and how to fix it, how should it be done?
Probably I will also have to add the _length field in the record, which will hold the size of the array the pointer is pointing to; this is not a problem.
Best regards,LUK
While the use of constants like this are okay in Delphi, I just want to add that it's in general not a very good idea to do things this way. Personally, if this code is in some unit, I would use something like this: (D2007 and higher)
Thus, the record gets a constructor which will fill it with the proper data. As a disadvantage, you can't declare it as a const anymore, if you want to use the constructor to fill it with data. However, you can solve this by using the following code in the Initialization section:
This code will declare the record as a global variable instead of constant, and fill it with your data.
Your constructor could look like this:
Which will fill the record with your data. Priyanka chopra husband name. However, you don't have to use the constructor to create records this way! It's just an added function.
To make it even more interesting, you can add properties for the two points and array, making the fields themselves private and only declaring read method for the properties. This way, you can still make sure it's content is read-only and stays read-only.
But what's the risk of using your code? Well, since you declare them all as constants, there isn't much risk, unless you allow assignable typed constants. ({$J+} is declared..) In that case, a piece of code could change a value in cOffsetsA and it would also change in cRec1. Is that what you want?
Anyway, by using a constructor and by initializing them in code, you make your code more dynamic. However, it still continues to stay a simple record type and the additional properties and methods won't change it's structure or size.
You will need Delphi 2007 or better for this, though..
It looks like I found the answer myself:
is a dynamic array type and setLength must be used with any variable of this type to allocate the memory. What I need is a pointer to an existing constant array, so the only thing which must be changed in order to fix the problem is the declaration of this type. It should look like:
and yes, I have to add the _length field in the records as low(pMyRec^.aOffsets^), high(..) and length(..) do not work.
Best regards,LUK
This question already has an answer here:
I have KnownFolderPath IDs declared as consts:
Backuptrans android whatsapp transfer crack. I want to define an ordered list of folder ids at compile time. I know I can do the following:
But this is not convenient maintainable code so I would like to rather use the names defined before. But this gives me compiler errors in Delphi XE3 (const expression expected):
I could define the FOLDERIDs as const strings like
but than I would have to convert the ids with StringToGUID() everywehere in the code. Isn't it somehow possible to define an ordered static / const list of const objects before runtime in Delphi?
This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.
In order to use the ID constants by name in the array declaration, you need to remove the TGuid type from the ID constant declarations, making them 'True constants' instead of 'Typed constants':
This is covered in Embarcadero's documentation:
True Constants
A true constant is a declared identifier whose value cannot change. For example:
declares a constant called MaxValue that returns the integer 237. The syntax for declaring a true constant is:
where identifier is any valid identifier and constantExpression is an expression that the compiler can evaluate without executing your program.
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Constant Expressions
A constant expression is an expression that the compiler can evaluate without executing the program in which it occurs. Constant expressions include numerals; character strings; true constants; values of enumerated types; the special constants True, False, and nil; and expressions built exclusively from these elements with operators, typecasts, and set constructors.
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Typed Constants
Typed constants, unlike true constants, can hold values of array, record, procedural, and pointer types. Typed constants cannot occur in constant expressions.
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Array Constants
To declare an array constant, enclose the values of the elements of the array, separated by commas, in parentheses at the end of the declaration. These values must be represented by constant expressions.
It is often useful to declare typed constants as well, which you can do without repeating the values, eg:
Alternatively, so the TGuid typed constants can match the Win32 API naming scheme:
Sadly the answer appears to be no. You an do the following
but then you would need to assign like this
Not sure if that is acceptable. You could put a class wrapper around it if you wish.