dynamic array in cpp

hello,

my problem is that i have a code in matlab and i want to rewrite it in cpp

in the matlab code i have dynamic arrays
with that i mean that too many times rows or columns of the table are deleted or a new one is inserted



but in cpp we know that the dimensions of an array are constant

what do you suggest me to use??
vector or lists or do it with array??

I think, you could use Linked List :wave:

An array is simply a block of memory. The dimensions of an array is directly related to the size of this block. If you want to resize your array, you need to allocate a larger memory block.

Quote:

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Originally Posted by Atheist

An array is simply a block of memory. The dimensions of an array is directly related to the size of this block. If you want to resize your array, you need to allocate a larger memory block.

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But in VB6, we could dynamically increment the array size by using the ReDim keyword...! So, how does VB dynamically allocate memory in this manner ? :confused:

Quote:

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Originally Posted by akhileshbc

But in VB6, we could dynamically increment the array size by using the ReDim keyword...! So, how does VB dynamically allocate memory in this manner ? :confused:

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VB6 will reallocate the memory block with a new size. If the Preserve keyword is used, the contents from the original memory block will be copied to the new memory block.

Code:

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'VB
Dim i(10) As Integer
'C
int *i = (int*)malloc(10 * sizeof(int));

'VB
ReDim i(20)
'C
free(i);
i = (int*)malloc(20 * sizeof(int));

'VB
ReDim Preserve i(40)
'C
i = (int*)realloc(i, 40 * sizeof(int))

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(Yes, I am aware that the VB array declarations will be 1 element larger than the C ones).

Quote:

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Originally Posted by akhileshbc

But in VB6, we could dynamically increment the array size by using the ReDim keyword...! So, how does VB dynamically allocate memory in this manner ? :confused:

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how you do dynamic allocation in vb.net, does it use the same ReDim?

Quote:

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Originally Posted by Aash

how you do dynamic allocation in vb.net, does it use the same ReDim?

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While this really is the wrong forum section for this kind of question; yes, ReDim is used to redimension arrays in VB.NET. That said, you normally wouldn't use arrays if you know that the size will change, you would use a collection such as a List(Of T).

Quote:

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Originally Posted by Atheist

While this really is the wrong forum section for this kind of question; yes, ReDim is used to redimension arrays in VB.NET. That said, you normally wouldn't use arrays if you know that the size will change, you would use a collection such as a List(Of T).

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Thanks :)

Thanks Atheist..:wave:

But I'm having another doubt...

When a array is being declared it allocates or reserves that space (consecutive memory locations)... But when we try to reallocate or extend the reserved space, what happens if there's no vacant space ?

For example, reserved for array from memory(assumption) location 2000 to 2010.
But from 2015 onwards, there's other data stored. So, if we try to enlarge the array space to 20 more, wouldn't it overlap ? :confused:

realloc() will extend the memory block if possible. If it isn't possible (That is, if the new memory block would overlap other reserved space) it will move the memory block to another address.
If the allocation can not be made at all, meaning that there is no more space, NULL is returned.

Quote:

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Originally Posted by Atheist

realloc() will extend the memory block if possible. If it isn't possible (That is, if the new memory block would overlap other reserved space) it will move the memory block to another address.
If the allocation can not be made at all, meaning that there is no more space, NULL is returned.

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Thanks..:wave: Got it...:thumb:

Sorry for hijacking this thread...:blush:

Quote:

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Originally Posted by Aash

how you do dynamic allocation in vb.net, does it use the same ReDim?

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An example would be:

vb.net Code:

Dim myUsers as new list(of string) '~~~ you could list of integers, long, etc..
 
myusers.add("Atheist")
myusers.add("Aash")
myusers.add("ABC")
'etc..
 
if myusers.contains("Aash") then messagebox.show("Hey, you are there !")
 
messagebox.show("Total number of items = " & myusers.count)
 
'~~~ there are several other useful methods like toarray() which will convert the items to an array, binarysearch(), etc....

PS: I have handwritten this code because my VS2010 is showing some "unhandled exception", when I try to open it..:D
:wave:

Quote:

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Originally Posted by akhileshbc

Thanks..:wave: Got it...:thumb:

Sorry for hijacking this thread...:blush:


An example would be:

vb.net Code:

Dim myUsers as new list(of string) '~~~ you could list of integers, long, etc..
 
myusers.add("Atheist")
myusers.add("Aash")
myusers.add("ABC")
'etc..
 
if myusers.contains("Aash") then messagebox.show("Hey, you are there !")
 
messagebox.show("Total number of items = " & myusers.count)
 
'~~~ there are several other useful methods like toarray() which will convert the items to an array, binarysearch(), etc....

PS: I have handwritten this code because my VS2010 is showing some "unhandled exception", when I try to open it..:D
:wave:

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Thanks Akhilesh :)