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Multi-dimensional array and pointers in C++?
Hi, In 1D I can declare an array like,
int *image = new int[W*H];
But in 2D how can I declare an array?
int *image = new int[W][H]; -- is it wrong??
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Nobody answered this correctly, here or at the duplicated question. I can't post my answer here, because this question is closed, but you can see it here: stackoverflow.com/questions/3367426/….TonyK– TonyK2011-06-03 11:40:21 +00:00Commented Jun 3, 2011 at 11:40
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@TonyK Both Nawaz and me did in fact answer this question correctly. Your way also works but I find it needlessly complicated, and at any rate inferior to using proper C++ classes.Konrad Rudolph– Konrad Rudolph2011-06-03 13:31:03 +00:00Commented Jun 3, 2011 at 13:31
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@Konrad: I suspect that your real objection to my answer is that it is needlessly simple.TonyK– TonyK2011-06-03 16:05:13 +00:00Commented Jun 3, 2011 at 16:05
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@TonyK Nothing of that sort. In fact, using vectors is vastly simpler. Now, what would your objection to our answers be?Konrad Rudolph– Konrad Rudolph2011-06-03 20:03:32 +00:00Commented Jun 3, 2011 at 20:03
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@Konrad: You only have to look at Nawaz's answer to see that it's ten times more complicated than mine. Your answer is fine, except that it didn't answer the OP's question: "How do I do this?" "DO NOT DO THIS!"TonyK– TonyK2011-06-03 20:27:18 +00:00Commented Jun 3, 2011 at 20:27
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4 Answers
int *image = new int[W][H]; -- is it wrong??
It will NOT compile. You should compile your code first, to know the answer of your question.
I think you want to do this:
//memory allocation
int **image = new int*[W];
for(size_t i = 0 ; i < W ; i++ )
image[i] = new int[H];
//use it as
for(size_t i = 0 ; i < W ; i++ )
for(size_t j = 0 ; j < H ; j++ )
image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H
//memory deallocation
for(size_t i = 0 ; i < W ; i++ )
delete [] image[i];
delete [] image;
But then why do all these when you've std::vector? You could use it which will do all these nasty thing itself. Here is how you should be using std::vector:
std::vector<std::vector<int> > image(W, std::vector<int>(H));
for(size_t i = 0 ; i < W ; i++ )
for(size_t j = 0 ; j < H ; j++ )
image[i][j] = some_value;
int value = image[20][30]; //get value at (20,30) assuming 20 < W and 30 < H
4 Comments
user570593
How can I declare a multi dimensional array??
Xeo
Heh, I just wanted to blame you for not trying to compiler yourself. :P At that time, the
NOT was not there.
Ozair Kafray
+1 for asking the questioner to compile.
Sarfaraz Nawaz
@Xeo: Hehe.. I had edited that within 3 seconds.. but you're faster than me :D
Since this is a question about C++:
Do not use C-style arrays or pointers (neither for 1D nor 2D arrays). Use the C++ data types, such as vector:
vector<int> image(W * H); // 1D array
vector<vector<int> > image(W, vector<int>(H)); // “2D” nested array.
This requires the vector standard header.
Comments
int** image = new int*[H];
for(int i = 0; i < H; i++)
image[i] = new int[W];
Comments
I use something like
int ** image....
