How to Convert a Multidimensional Array to Pointers for Use in C Library Functions?

Converting Multidimensional Arrays to Pointers in C

In C , multidimensional arrays and pointers to arrays provide different mechanisms to represent and manipulate data structures. Understanding how to interconvert between these representations is crucial for effective programming.

Consider a scenario where you have a program with a 4x4 double-precision floating-point matrix stored in a multidimensional array startMatrix. You want to compute its inverse using a library function that takes double pointers (double **) as input.

The intuitive approach might be to simply cast the startMatrix to a double pointer:

<code class="cpp">MatrixInversion((double**)startMatrix, 4, (double**)inverseMatrix));</code>

However, this approach is incorrect. Double pointers and multidimensional arrays are not interchangeable data structures.

The correct approach is to create an array of pointers to the beginning of each row in startMatrix. For example, you can create index arrays startRows and inverseRows as follows:

<code class="cpp">double *startRows[4] = { startMatrix[0], startMatrix[1], startMatrix[2], startMatrix[3] };
double *inverseRows[4] = { /* same for inverseMatrix */ };</code>

These arrays serve as indices into the matrices, making them compatible with the library function:

<code class="cpp">MatrixInversion(startRows, 4, inverseRows);</code>

Once the inversion is complete, the result will be stored in inverseMatrix correctly. This indirect approach provides a bridge between multidimensional arrays and pointers, enabling you to use specialized functions that require pointer-based input.

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