/* In C */
FooSeq foo_seq = ...;
void *app_buffer;
...
long length = FooSeq_get_length(&foo_seq);
if (length > APP_BUFFER_SIZE) {

  // print ERROR message

}
memcpy(app_buffer, FooSeq_get_reference(&foo_seq,0), length * sizeof(Foo));

// In C++
FooSeq foo_seq;
void *app_buffer;
...
long length = foo_seq.length();
if (length > APP_BUFFER_SIZE) {

  // print ERROR message

}
memcpy(app_buffer, &foo_seq[0], length * sizeof(Foo));