This builds off of the monster schema example. If I partially fill a flatbuffer such as in the official test.cpp.
Relevant lines also copied below
// Create a mostly empty FlatBuffer.
flatbuffers::FlatBufferBuilder nested_builder;
auto nmloc = CreateMonster(nested_builder, nullptr, 0, 0,
nested_builder.CreateString("NestedMonster"));
FinishMonsterBuffer(nested_builder, nmloc);
How can I modify the inventory part of the schema from nested_builder after already calling FinishMonsterBuffer(nested_builder, nmloc);?
Things I've tried (related to test.cpp):
std::string bfbsfile;
bool found = flatbuffers::LoadFile( "./monster_schema.bfbs", true, &bfbsfile );
const reflection::Schema& schema = *reflection::GetSchema( bfbsfile.c_str() );
auto root_table = schema.root_table();
auto fields = root_table->fields();
// The above works fine I've tested the fields and verified the schema.
// I'm unsure of the code below.
// First we put the FlatBuffer inside an std::vector.
std::vector<uint8_t> resizingbuf(
nested_builder.GetBufferPointer(),
nested_builder.GetBufferPointer() + nested_builder.GetSize());
// Get the root.
// This time we wrap the result from GetAnyRoot in a smartpointer that
// will keep rroot valid as resizingbuf resizes.
auto rroot = flatbuffers::piv(flatbuffers::GetAnyRoot(resizingbuf.data()),
resizingbuf);
// Now lets try to extend a vector by 100 elements (0 -> 110).
auto &inventory_field = *fields->LookupByKey("inventory");
// I don't think this works either if it doesn't already exist.
auto rinventory = flatbuffers::piv(
flatbuffers::GetFieldV<uint8_t>(**rroot, inventory_field), resizingbuf);
// This line silently fails probably because *rinventory is probably a nullptr
// but I don't know how to set it after having already
// called FinishMonsterBuffer(nested_builder, nmloc);.
flatbuffers::ResizeVector<uint8_t>(schema, 110, 50, *rinventory,
&resizingbuf);
// Try to print it but prints nothing.
// printf("%hhu", rinventory->Get(10));
Apologies in advance for the title I'm not quite sure how to phrase the exact problem or question. Let me know if more context is needed or part of the question doesn't make sense.
Disclaimer: Flatbuffers doesn't generally allow mutating a vector after the buffer has been finished. However, we do have some advanced APIs in the reflection API for doing such mutations, but are generally slow and not recommended.
We don't support the case of resizing a null vector. We store null within the vtable and there is no data/size information in the buffer related to a null vector. Therefore there is nothing to resize.
You may try inserting a empty vector instead, as that should place the necessary data/size information into the buffer that can be later resized.