Why use array size 1 instead of pointer?

Question

In one C++ open source project, I see this.

struct SomeClass {
  ...
  size_t data_length;
  char data[1];
  ...
}

What are the advantages

Answer 1

This is usually a quick(and dirty?) way of avoiding multiple memory allocations and deallocations, though it's more C stylish than C++.

That is, instead of this:

struct SomeClass *foo = malloc(sizeof *foo);
foo->data = malloc(data_len);
memcpy(foo->data,data,data_len);

....
free(foo->data);
free(foo);

You do something like this:

struct SomeClass *foo = malloc(sizeof *foo + data_len);
memcpy(foo->data,data,data_len);

...
free(foo);

In addition to saving (de)allocation calls, this can also save a bit of memory as there's no space for a pointer and you could even use space that otherwise could have been struct padding.