C++ finding something in vector - c++

Question

I have an vector like this:
struct RIFT_MONSTER_SPAWN
{
DWORD dwWorldId;
D3DXVECTOR3 vPos;
};
vector<RIFT_MONSTER_SPAWN> vecMSpawn;
As you can see it will hold 2 values dwWorldId and D3DXVECTOR3 vPos;
vPos will hold x,y,z value.
Now what I want to do is looping true the vector and if the worldId matches the worldId that is beeing passed. It should return the vPos that is releated to the worldId.
If have use std::find find_all and count.
But it always returns the error
binary == no operator found which takes a left hand operator of type
So I am an bit stuck on this. Any help would be appreciated.
With kind regards.
Here is the code that is giving me problems
void CRiftMatch::GetMoverSpawnPoints(dwWorldId)
{
std::vector<RIFT_MONSTER_SPAWN> vecSpawn = CRiftMng::GetInstance()->m_vecMSpawnPoint;
std::vector<RIFT_MONSTER_SPAWN>::iterator it = std::find(vecSpawn.begin(), vecSpawn.end(), dwWorldId);
OUTPUTDEBUGSTRING("\n GetMoverSpawn %d", *it);
}
m_vecMSpawnPoint is defined in .h file as
vector<RIFT_MONSTER_SPAWN> m_vecMSpawnPoint;
Also to fill it i am using this code
while (Lua.TableLoop(-2))
{
RIFT_MONSTER_SPAWN rSpawnPoint;
rSpawnPoint.dwWorldId = static_cast<int>(CScript::GetDefineNum(Lua.GetFieldToString(-1, "dwWorldId")));
rSpawnPoint.vPos.x = static_cast<float>(Lua.GetFieldToNumber(-1, "x"));
rSpawnPoint.vPos.y = static_cast<float>(Lua.GetFieldToNumber(-1, "y"));
rSpawnPoint.vPos.z = static_cast<float>(Lua.GetFieldToNumber(-1, "z"));
m_vecMSpawnPoint.push_back(rSpawnPoint);
Lua.Pop(1);
}

Answer 1

You have to modify your struct to be able compare values during find:
struct RIFT_MONSTER_SPAWN
{
DWORD dwWorldId;
D3DXVECTOR3 vPos;
bool operator () ( const RIFT_MONSTER_SPAWN & m ) const
{
return m.dwWorldId == dwWorldId;
}
};
RIFT_MONSTER_SPAWN monsterToFind;
monsterToFind.dwWorldId = dwWorldId;
it = std::find_if( vecSpawn.begin(), vecSpawn.end(), monsterToFind);
Maybe just a type, but in your code, you have
void CRiftMatch::GetMoverSpawnPoints(dwWorldId)
but it should be
void CRiftMatch::GetMoverSpawnPoints(DWORD dwWorldId)

Answer 2

You could pass a predicate (which can be a lambda) to std::find_if so code
auto it = std::find_if(vecSpawn.begin(), vecSpawn.end(),
[&] (const struct RIFT_MONSTER_SPAWN& sp)
{return sp.dxWorldId == dwWorldIt;});
But in such a case I would simply use a for loop (because I find that more readable):
int ix=0;
for (auto&sp : vecSpawn) {
if (sp.dxWorldId == dwWorldIt)
return vecSpawn.begin() + ix;
ix++;
}

Answer 3

With range/v3, you may simply do
auto it = ranges::find(vecSpawn, dwWorldIt, &RIFT_MONSTER_SPAWN::dxWorldId);
else you have to use more verbose
auto it = std::find_if(vecSpawn.begin(), vecSpawn.end(),
[&](const RIFT_MONSTER_SPAWN& e) {
return e.dxWorldId == dwWorldIt;
});