What I am asking about is the well known "last member of a struct has variable length" trick. It goes something like this:
struct T {
int len;
char s[1];
};
struct T *p = malloc(sizeof(struct T) + 100);
p->len = 100;
strcpy(p->s, "hello world");
Because of the way that the struct is laid out in memory, we are able to overlay the struct over a larger than necessary block and treat the last member as if it were larger than the 1 char specified.
So the question is: Is this technique technically undefined behavior?. I would expect that it is, but was curious what the standard says about this.
PS: I am aware of the C99 approach to this, I would like the answers to stick specifically to the version of the trick as listed above.