2d array pointer

What's wrong with this?

Code:

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    double  coslu[8][] = 0;

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devstudio complains about a missing subscript or some nonsense.
How do I fix it.

Sensible suggestions only please

The array needs to have a fixed size. For instance:

Code:

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double  coslu[8][8] = {0.0}; //initialize all elements to 0.0

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Laitinen

if youre going to allocate that 2-d array later just do

double coslu** = 0;

if youre trying to initialize all values to 0 then first off you need definite bounds for the array in both dimensions and then you have to loop through and set them all to 0 manually

Quote:

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Originally Posted by laitinen

The array needs to have a fixed size. For instance:

Code:

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double  coslu[8][8] = {0.0}; //initialize all elements to 0.0

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Laitinen

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I'm not defining an array.

Quote:

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Originally Posted by c94wjpn

I'm not defining an array.

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ok mind telling us what you're trying to do?

Quote:

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Originally Posted by Ultimate Hammer

if youre going to allocate that 2-d array later just do

double coslu** = 0; /// error stars in the wrong place

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you are defining a pointer to an array of pointers.
From looking at the memory blocks in a debugger, it is clear that

double coslu1[8][8];

does not create an array of pointers.

hence

double** p = coslu1;

will not succeed.

Quote:

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Originally Posted by Ultimate Hammer

ok mind telling us what you're trying to do?

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Trying to define a pointer to a 2d array which has a stride of 8.
If I know that my doubles are in a consecutive memory block at location p, and the stride is 8, then the notations

p[y][x]
and
p[y*8 + x]

should be equivalent, and hence I should be able to define

double * q = 0; ///ok

also

double q[][8] = 0; /// not ok.

Quote:

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Originally Posted by c94wjpn

Trying to define a pointer to a 2d array which has a stride of 8.
If I know that my doubles are in a consecutive memory block at location p, and the stride is 8, then the notations

p[y][x]
and
p[y*8 + x]

should be equivalent, and hence I should be able to define

double * q = 0; ///ok

also

double q[][8] = 0; /// not ok.

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What are you trying to do by assigning it to 0?

An array is not just a pointer, it occupies a space on the stack. So it cannot (or should not) be NULLed, if that's what you're trying to do. If you're trying to initialize all elements of the array to 0, how is the compiler supposed to know how many elements there are if you don't explicitly supply a second dimension?

Quote:

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Originally Posted by Hermit

What are you trying to do by assigning it to 0?

An array is not just a pointer, it occupies a space on the stack. So it cannot (or should not) be NULLed, if that's what you're trying to do. If you're trying to initialize all elements of the array to 0, how is the compiler supposed to know how many elements there are if you don't explicitly supply a second dimension?

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engage your brain please.

I can set a pointer to NULL if I want to - I'm not accessing it yet.

I have explicitly supplied a second dimension :

double q[][8] = 0; /// not ok. THE 8 IS THE SECOND DIMENSION.

sensible responses only

Quote:

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Originally Posted by c94wjpn

engage your brain please.

I can set a pointer to NULL if I want to - I'm not accessing it yet.

I have explicitly supplied a second dimension :

double q[][8] = 0; /// not ok. THE 8 IS THE SECOND DIMENSION.

sensible responses only

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I meant both dimensions. If one dimension is omitted, then the compiler at least needs to be able to deduce that dimension from the initialization list. For example:

Code:

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double q[][8] = { {0.0}, {0.0}, {0.0} }; // okay, first dimension is 3

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This is only relevant if you're actually aiming at initialization. I don't know what to suggest if you're determined to somehow NULL an array on the stack. It can't be done, and there's no reason to do it.

And please, drop the condescending tone. Your question is vague at best and if you'd like a sensible answer you'd do best to be a little cooperative.

Quote:

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Originally Posted by Hermit

I meant both dimensions. If one dimension is omitted, then the compiler at least needs to be able to deduce that dimension from the initialization list. For example:

Code:

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double q[][8] = { {0.0}, {0.0}, {0.0} }; // okay, first dimension is 3

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This is only relevant if you're actually aiming at initialization. I don't know what to suggest if you're determined to somehow NULL an array on the stack. It can't be done, and there's no reason to do it.

And please, drop the condescending tone. Your question is vague at best and if you'd like a sensible answer you'd do best to be a little cooperative.

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well I think I've outgrown codeguru. Maybe I should quit.

I'm not creating an array. I'm creating a pointer to a memory block.

I think I shall take my problem elsewhere.

Quote:

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Originally Posted by c94wjpn

well I'm not creating an array.

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So why did you post this:

Code:

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double  coslu[8][] = 0;

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?

What is that supposed to mean? Tell us in your own words what that is supposed to do or what you thought it would do, if it isn't trying to create an array.

Quote:

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I'm creating a pointer to a memory block.

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I see no "*" syntax anywere in the declaration above. So you are not creating a pointer to anything in your initial post. You are doing something with trying to declare an array -- what exactly is still a mystery.

Quote:

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I think I shall take my problem elsewhere.

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Unless you explain a little better what you're trying to do, expect the same, if not worse responses from whatever site you take your very vague question to.

Regards,

Paul McKenzie

I think this guy has no idea of what is talking about, that is all. Let him go elsewhere. He probably guilts other people for his ignorance and in his frustration he just pretends to know what is going on, now don't ask me why he made any question in the first place (needs a psicologist's help not a programmer's)

Are you trying to do something like this?

Code:

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double  coslu[8][8];

double *p_coslu = &coslu[0][0]; // Pointer to the start of the 8x8 block of doubles.

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And that would be just like:

double coslu[8][8];

double *p_coslu = coslu;

I'm thinking, guessing from what he wrote on the title he wanted this:

double * P_coslu = &coslu[8][0]; // 2nd array?