Passing two-dimensional array via pointer

by

If you insist on the above declaration of foo, i.e.

void foo(float **pm)

and on using a built-in 2D array, i.e.

float m[4][4];

then the only way to make your foo work with m is to create an extra “row index” array and pass it instead of m

...
float *m_rows[4] = { m[0], m[1], m[2], m[3] };
foo(m_rows);

There no way to pass m to foo directly. It is impossible. The parameter type float ** is hopelessly incompatible with the argument type float [4][4].

Also, since C99 the above can be expressed in a more compact fashion as

foo((float *[]) { m[0], m[1], m[2], m[3] });

P.S. If you look carefully, you’ll that this is basically the same thing as what Carl Norum suggested in his answer. Except that Carl is malloc-ing the array memory, which is not absolutely necessary.

More Related Contents:

  1. C 3d array pointer decay with & and without &
  2. whats the difference between dynamic memory allocation and normal memory allocation?
  3. C array pointer increment
  4. Value changing when I pass array into function
  5. C pointer to array/array of pointers disambiguation
  6. C: differences between char pointer and array [duplicate]
  7. Create a pointer to two-dimensional array
  8. What exactly is the array name in c?
  9. How to pass a 2D array by pointer in C?
  10. Should I use char** argv or char* argv[]?
  11. Efficiency: arrays vs pointers
  12. Pass a two dimensional array to a function of constant parameter
  13. Pointer vs array in C, non-trivial difference
  14. Changing array inside function in C
  15. Does C99 guarantee that arrays are contiguous?
  16. What’s a modern term for “array/pointer equivalence”?
  17. Is it possible to allocate array inside function and return it using reference?
  18. C – SizeOf Pointers
  19. Why can´t we assign a new string to an char array, but to a pointer?
  20. C pointers and arrays/ ‘sizeof’ operator [duplicate]
  21. Doesn’t a 2D array decay to pointer to pointer
  22. How to include a dynamic array INSIDE a struct in C?
  23. Are a, &a, *a, a[0], &a[0] and &a[0][0] identical pointers?
  24. How can I return a character array from a function in C?
  25. “int *nums = {5, 2, 1, 4}” causes a segmentation fault
  26. Array of size 0 at the end of struct [duplicate]
  27. C difference between *[] and **
  28. Reliably determine the number of elements in an array
  29. Difference between dereferencing pointer and accessing array elements
  30. Difference between pointer to pointer and pointer to array?

Leave a Comment