FlatBuffers中VectorLength返回size_t而Vector::size返回uoffset_t的原因是什么

该类型差异有时会在64位编译场景下引发问题。若没有特殊的设计考量，建议为VectorLength()和Vector::size()统一索引类型。

如下示例中，调用print_first_n_of_inventory时传入VectorLength的返回值就需要做强制类型转换：

#include <flatbuffers/flatbuffers.h>
#include <tests/monster_test_generated.h>
#include <iostream>

using namespace flatbuffers;
using namespace MyGame::Example;

void print_first_n_of_inventory(const Vector<uint8_t> * pInventory, uoffset_t n)
{
    for (uoffset_t i = 0; i < n; ++i)
    {
        auto val = pInventory->Get(i);
        std::cout << val << "\n";
    }
}

int main(int, char * argv[])
{
    auto * pMonster = GetMonster(argv[1]);
    auto * pInventory = pMonster->inventory();

    print_first_n_of_inventory(pInventory, 2);
    print_first_n_of_inventory(pInventory, pInventory->size());

    // warning C4267: 'argument': conversion from 'size_t' to 'flatbuffers::uoffset_t', possible loss of data
    print_first_n_of_inventory(pInventory, VectorLength(pInventory));

    return 0;
}

当前调用VectorLength时会触发C4267编译告警，提示存在size_t到uoffset_t转换的数据丢失风险。

内容的提问来源于stack exchange，提问作者Stefan F.