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I have a 3 dimensional array and want to create a pointer to the 2nd dimension.

uint32_t m0[4096][256][8];
uint32_t (*m1)[256][8] = &m0[0];
uint32_t *m2 = m1[2];      //<- warning: initialization from incompatible pointer type

// do something with m2[0], m2[1].... m2[7]

Obviously there is something with the above code. What is it?

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3 Answers 3

Reset to default
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m1[2] is *(m1+2).
Type of *(m1+2) is the same as the type of *m1, which is unit32_t [256][8].

For that reason, the following line is wrong.

uint32_t* m2 = m1[2];

What you need to use is:

uint32_t* m2 = (*m1)[2];
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5 Comments

fixed the line, made no difference, same error message
@poby, not sure why. It works for me on my desktop and online at ideone.com/pHYTZz.
This is weird! It actually works only if the m2[0] = 10; line is included. If I don't do an assignation, I get the above error.
@poby, the error is probably about an unused variable, but that's only a guess.
@R.Sahu, yeah you're right, I didn't notice the error was different.
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your 2nd dimension is not uint32_t * it's simply m[n], or exactly as you've declared m1. m1[n] is uint32_t[8]

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That's not possible because the second dimension's values aren't stored next to each other in memory.

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1 Comment

From the accepted answer I take that @poby means a flattened array of the last two dimensions. My answer isn't relevant

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