Saturday, May 22, 2010

Multidimensional arrays with GCC's variable length arrays

GCC's extensions allow you to do some crazy things with multidimensional arrays. For C99, GCC implements variable-length arrays. So a declaration like this:

int matrix[a][b + 1];

Can be passed by reference to a function with this prototype:

void foo(int a, int b, int matrix[a][b+1]);

Or, if you want to get really crazy, you can use forward declarations and change around the parameter order:

void foo(int a; int b; int matrix[a][b+1], int a, int b);

No malloc needed! Much better than the old way.