Occasional SEGFAULT in my c++ code with flatbuffers - c++

Question

I'm working on my C++ project with flatbuffers. I started with google's online example and wrote a google test. However, this test sometimes failed with SEGFAULT.
Following are the code snippets.
// moster.fbs
namespace MyGame.Sample;
enum Color:byte { Red = 0, Green, Blue = 2 }
union Equipment { Weapon } // Optionally add more tables.
struct Vec3 {
x:float;
y:float;
z:float;
}
table Monster {
pos:Vec3; // Struct.
mana:short = 150;
hp:short = 100;
name:string;
friendly:bool = false (deprecated);
inventory:[ubyte]; // Vector of scalars.
color:Color = Blue; // Enum.
weapons:[Weapon]; // Vector of tables.
equipped:Equipment; // Union.
path:[Vec3]; // Vector of structs.
}
table Weapon {
name:string;
damage:short;
}
root_type Monster;
// test.cpp
#include <fstream>
#include <string>
#include "gtest/gtest.h"
#include "monster_generated.h"
using namespace MyGame::Sample;
void WriteMonsterToFile(const std::string& filename)
{
// Build up a serialized buffer algorithmically:
flatbuffers::FlatBufferBuilder builder;
// First, lets serialize some weapons for the Monster: A 'sword' and an 'axe'.
auto weapon_one_name = builder.CreateString("Sword");
short weapon_one_damage = 3;
auto weapon_two_name = builder.CreateString("Axe");
short weapon_two_damage = 5;
// Use the `CreateWeapon` shortcut to create Weapons with all fields set.
auto sword = CreateWeapon(builder, weapon_one_name, weapon_one_damage);
auto axe = CreateWeapon(builder, weapon_two_name, weapon_two_damage);
// Create a FlatBuffer's `vector` from the `std::vector`.
std::vector<flatbuffers::Offset<Weapon>> weapons_vector;
weapons_vector.push_back(sword);
weapons_vector.push_back(axe);
auto weapons = builder.CreateVector(weapons_vector);
// Second, serialize the rest of the objects needed by the Monster.
auto position = Vec3(1.0f, 2.0f, 3.0f);
auto name = builder.CreateString("MyMonster");
unsigned char inv_data[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
auto inventory = builder.CreateVector(inv_data, 10);
// Shortcut for creating monster with all fields set:
auto orc = CreateMonster(builder, &position, 150, 80, name, inventory,
Color_Red, weapons, Equipment_Weapon, axe.Union());
builder.Finish(orc); // Serialize the root of the object.
// We now have a FlatBuffer we can store on disk or send over a network.
std::ofstream outfile(filename, std::ios::binary);
outfile.write((char*)builder.GetBufferPointer(), builder.GetSize());
outfile.flush();
outfile.close();
}
TEST(FlatbuffersTest, Monster)
{
WriteMonsterToFile("monster.bin");
// ** file/network code goes here :) **
std::ifstream infile;
infile.open("monster.bin", std::ios::binary | std::ios::in);
infile.seekg(0, std::ios::end);
int length = infile.tellg();
infile.seekg(0, std::ios::beg);
char* data = new char[length];
infile.read(data, length);
infile.close();
// Get access to the root:
auto monster = GetMonster(data);
delete[] data;
// Get and test some scalar types from the FlatBuffer.
EXPECT_EQ(monster->hp(), 80);
EXPECT_EQ(monster->mana(), 150);
EXPECT_EQ(monster->name()->str(), "MyMonster");
// Get and test a field of the FlatBuffer's `struct`.
auto pos = monster->pos();
EXPECT_EQ(pos->z(), 3.0f);
// Get a test an element from the `inventory` FlatBuffer's `vector`.
auto inv = monster->inventory();
EXPECT_EQ(inv->Get(9), 9);
// Get and test the `weapons` FlatBuffers's `vector`.
std::string expected_weapon_names[] = {"Sword", "Axe"};
short expected_weapon_damages[] = {3, 5};
auto weps = monster->weapons();
for (unsigned int i = 0; i < weps->size(); i++) {
EXPECT_EQ(weps->Get(i)->name()->str(), expected_weapon_names[i]);
EXPECT_EQ(weps->Get(i)->damage(), expected_weapon_damages[i]);
}
// Get and test the `Equipment` union (`equipped` field).
EXPECT_EQ(monster->equipped_type(), Equipment_Weapon);
auto equipped = static_cast<const Weapon*>(monster->equipped());
EXPECT_EQ(equipped->name()->str(), "Axe");
EXPECT_EQ(equipped->damage(), 5);
}
test output:
$ ctest --rerun-failed --output-on-failure
Test project /root/cpcos/build_linux64
Start 3: FlatbuffersTest.Monster
1/1 Test #3: FlatbuffersTest.Monster ..........***Exception: SegFault 0.01 sec
Running main() from /home/conan/w/BuildSingleReference/.conan/data/gtest/1.11.0/_/_/build/7320405f83ec32d8556b524cdda87ee295bb7b84/source_subfolder/googletest/src/gtest_main.cc
Note: Google Test filter = FlatbuffersTest.Monster
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from FlatbuffersTest
[ RUN ] FlatbuffersTest.Monster
/root/cpcos/tests/flatbuffers_gtest.cpp:71: Failure
Expected equality of these values:
monster->hp()
Which is: 100
80
0% tests passed, 1 tests failed out of 1
Total Test time (real) = 0.04 sec
The following tests FAILED:
3 - FlatbuffersTest.Monster (SEGFAULT)
Errors while running CTest
I compiled the code and ran it many times, strangely, it sometimes PASS while sometimes failed with SEGFAULT.
What did I do wrong?
Thanks.