On Tue, May 14, 2013 at 9:41 AM, Olivier Langlois <olivier@olivierlanglois.net> wrote:
On Tue, 2013-05-14 at 08:52 +0200, Martti Kühne wrote:
Sorry if this is OT and a dumb question, but are you sure you want
On Mon, May 13, 2013 at 8:20 PM, LANGLOIS Olivier PIS -EXT <olivier.pis.langlois@transport.alstom.com> wrote: [...]
struct B { int numelem; /* * Old C trick to define a dynamically sizable array just by allocating * sizeof(B) + (numelem-1)*sizeof(A) memory. */ A item[1]; };
one item vs.
That is a old C trick when STL container did not exist. The other options would be to replace the 1 item array with pointer but then you would have to do 2 malloc. 1 for struct B 1 for the array of A.
Maybe my usage of B array did obfuscate the pattern. An another way to use it is:
B *p = (B *)malloc(sizeof(B) + (numelem-1)*sizeof(A));
That way you can define dynamically the say of the 'item' array. This pattern dates back way before C99 standard which did, I think, introduce dynamic array where you could write
B array[var];
C99 variable-length arrays are put on the stack, they're just a standard alloca. The standard/valid way of having a flexible-length struct member is `array[]` without a given size - no workaround is needed.