C++ function information

[mackerel]

Hi, in this link otland/forgottenserver

you can see the function I need help with (just some explanation).

There are 3 if statements that are important to me but I am just curious about 1

The first one will execute once you deselect the target by yourself. The third one will execute if you cannot select the target, in this case that could be an NPC. But I am not sure about the second one as I couldn't really print anything to the console

this one here:

Creature* attackCreature = getCreatureByID(creatureId);
if (!attackCreature) {

If anyone could provide me with some info that would be great

if (player->getAttackedCreature() && creatureId == 0) {
        player->setAttackedCreature(nullptr);
        player->sendCancelTarget();
        return;
    }

    Creature* attackCreature = getCreatureByID(creatureId);
    if (!attackCreature) {
        player->setAttackedCreature(nullptr);
        player->sendCancelTarget();
        return;
    }

    ReturnValue ret = Combat::canTargetCreature(player, attackCreature);
    if (ret != RETURNVALUE_NOERROR) {
        player->sendCancelMessage(ret);
        player->sendCancelTarget();
        player->setAttackedCreature(nullptr);
        return;
}

 

[samco]

Hi, in this link otland/forgottenserver

you can see the function I need help with (just some explanation).

There are 3 if statements that are important to me but I am just curious about 1

The first one will execute once you deselect the target by yourself. The third one will execute if you cannot select the target, in this case that could be an NPC. But I am not sure about the second one as I couldn't really print anything to the console

this one here:

Creature* attackCreature = getCreatureByID(creatureId);
if (!attackCreature) {

If anyone could provide me with some info that would be great

if (player->getAttackedCreature() && creatureId == 0) {
        player->setAttackedCreature(nullptr);
        player->sendCancelTarget();
        return;
    }

    Creature* attackCreature = getCreatureByID(creatureId);
    if (!attackCreature) {
        player->setAttackedCreature(nullptr);
        player->sendCancelTarget();
        return;
    }

    ReturnValue ret = Combat::canTargetCreature(player, attackCreature);
    if (ret != RETURNVALUE_NOERROR) {
        player->sendCancelMessage(ret);
        player->sendCancelTarget();
        player->setAttackedCreature(nullptr);
        return;
}

I think its just a control in case the creature is killed at the same moment you target it.

 

[mackerel]

I think its just a control in case the creature is killed at the same moment you target it.

hmm maybe, there is no way to test it though

 

[jo3bingham]

To expand on what @samco said, the main purpose of getCreatureById() is to make sure a creature with that id actually exists in memory. If it exists, a pointer to the creature is returned, otherwise nullptr is returned. Without the check to see if a valid pointer is returned [if (!attackCreature)] then Combat::canTargetCreature() would crash the server because of a null-pointer-dereference.

One way you could test this is to craft your own AttackCreature packet client-side and pass an invalid creature id (like 0). There's multiple ways of doing this, but none are simple unless you know how to inject a DLL into the client and hook the AttackCreature packet constructor, or set up a proxy and capture the AttackCreature packet and modify it.

 

[samco]

To expand on what @samco said, the main purpose of getCreatureById() is to make sure a creature with that id actually exists in memory. If it exists, a pointer to the creature is returned, otherwise nullptr is returned. Without the check to see if a valid pointer is returned [if (!attackCreature)] then Combat::canTargetCreature() would crash the server because of a null-pointer-dereference.

One way you could test this is to craft your own AttackCreature packet client-side and pass an invalid creature id (like 0). There's multiple ways of doing this, but none are simple unless you know how to inject a DLL into the client and hook the AttackCreature packet constructor, or set up a proxy and capture the AttackCreature packet and modify it.

Or if you are compiling in VS, just attach the process to the debugger, and set the attackCreature to null

 

[jo3bingham]

Or if you are compiling in VS, just attach the process to the debugger, and set the attackCreature to null

This would work as well. @mackerel if you do this, make sure you use a Debug build as a Release build can give you some unexpected behaviour with the debugger.

 

[mackerel]

thank you guys, very helpful