Question

I have a function(in some library) whose signature is this:

extern LIB3DSAPI void lib3ds_mesh_calculate_face_normals(Lib3dsMesh *mesh, float (*face_normals)[3]);

what does it expect in second argument?

I tried this:

        float   *norm_verts[3];
        norm_verts=(float(*)[3])malloc(3*sizeof(float[3])*mesh->nfaces);
        lib3ds_mesh_calculate_face_normals(mesh, norm_faces);

on the second line, it says Expression must be modifiable value and the third line says argument of type float** is incompatible with parameter of type float(*)[3]

My intuition was that float* [3] is just 3 pointers but why the hell is the * wrapped in brackets?

Answer 1

The * is wrapped in brackets to give it tighter binding. The 2nd arg to lib3ds_mesh_calculate_face_normals is read “face_normals is a pointer to an array of 3 float`.

Try:

float   (*norm_verts)[3];
norm_verts=(float(*)[3])malloc(sizeof(*norm_verts)*mesh->nfaces);
lib3ds_mesh_calculate_face_normals(mesh, norm_vets);