Assign a pointer by a pointer to multidimensional array in function [duplicate]

Question

void print_first_n_row(double **matrix, int n, int row_size) {
 double (*abc)[row_size];
 abc=matrix;}

I am having assignment from incompatible pointer type [-Wincompatible-pointer-types] abc=matrix error. How can I solve this?

Answer 1

A matrix is an abstract data type. How you implement it is an implementation detail.

In this answer I detailed how you could implement such a type in C.

Multi-dimensional arrays don't really exist in C. C just have arrays of arrays, or arrays of pointers -or other types, including arrays of scalars. Check by reading n1570 (the C11 standard).

I am having assignment from incompatible pointer type [-Wincompatible-pointer-types] abc=matrix error. How can I solve this?

Either think in abstract data types terms, or read more about C dynamic memory allocation (consider using flexible array members) and about the C programming language.

You'll find many examples of matrix-related source code on github or gitlab and elsewhere.

Answer 2

Note: This answer is just regarding the error message, not the logic behind passing pointers to a matrix.

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"I am having assignment from incompatible pointer type [-Wincompatible-pointer-types] abc=matrix error. How can I solve this?"

double (*abc)[row_size]; - abc is a pointer to an array of double.

double **matrix - matrix is a pointer to a pointer to double.

There is a mismatch. * vs. **.

You can´t assign the value of a pointer to a pointer to double to a pointer to an array of double.

Change double (*abc)[row_size]; to double **abc or double (**abc)[row_size]; or just use matrix if abc isn´t needed otherwise.