On 28/02/15 16:27, Manuel López-Ibáñez wrote: > cam_xyz[0] is type 'double [3]', thus I don't think you should cast it > to 'double *', but in this respect I am just going by intuition, not > by an actual reference to the standard. On the other hand, > &cam_xyz[0][0] should have type 'double *', and the standard does say > that the data is contiguously allocated, yet the c-faq says that > ((double *)(&cam_xyz[0][0]))[j] "is not in strict conformance with the > ANSI C Standard; according to an official interpretation" > (http://c-faq.com/aryptr/ary2dfunc2.html), although without a > reference to the standard, I have no idea what that means. Here we go. :-) ANSI defines E1[E2] as (*((E1)+(E2))) and (therefore) cam_xyz[i][j] as *((*(cam_xyz+i))+j) ISO/IEC 9899:1999, 6.5.1 Primary expressions: "Successive subscript operators designate an element of a multidimensional array object. If E is an n-dimensional array (n ≥ 2) with dimensions i × j × . . . × k, then E (used as other than an lvalue) is converted to a pointer to an (n − 1)-dimensional array with dimensions j × . . . × k. If the unary * operator is applied to this pointer explicitly, or implicitly as a result of subscripting, the result is the pointed-to (n − 1)-dimensional array, which itself is converted into a pointer if used as other than an lvalue." Therefore the result of the inner *(cam_xyz+i) is a one-dimensional array. You have no permission to dereference beyond the end of that array, and any attempt to do so is UB. Andrew.
