Trailing Array Idiom

Question

What is Trailing Array Idiom ?

P.S : Googling this term gives The vectors are implemented using the trailing array idiom, thus they are not resizeable without changing the address of the vector object itself.

Answer 1

If you mean the trailing array idiom mentioned in the GCC source code (where your quote comes from), it seems to refer to the old C trick to implement a dynamic array:

typedef struct {
    /* header */
    size_t nelems;

    /* actual array */
    int a[1];
} IntVector;

where an array would be created with

IntVector *make_intvector(size_t n)
{
    IntVector *v = malloc(sizeof(IntVector) + sizeof(int) * (n-1));
    if (v != NULL)
        v->nelems = n;
    return v;
}