Method GetOptionalFieldOffset

Libs/flatbuffers/flatbuffers.h:2680–2688

This gets the field offset for any of the functions below it, or 0 if the field was not present.

  // This gets the field offset for any of the functions below it, or 0
  // if the field was not present.
  voffset_t GetOptionalFieldOffset(voffset_t field) const {
    // The vtable offset is always at the start.
    auto vtable = GetVTable();
    // The first element is the size of the vtable (fields + type id + itself).
    auto vtsize = ReadScalar<voffset_t>(vtable);
    // If the field we're accessing is outside the vtable, we're reading older
    // data, so it's the same as if the offset was 0 (not present).
    return field < vtsize ? ReadScalar<voffset_t>(vtable + field) : 0;
  }

  template<typename T> T GetField(voffset_t field, T defaultval) const {
    auto field_offset = GetOptionalFieldOffset(field);