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Crash (this was nullptr, access violation)


I already got some Access Violation but I can't figure out why I get one this one time. On VS Debug I got a this was nullptr error, but I don't use pointer in the method so I don't get why I get it. And on error stacks side, I got an Access Violation.

The problem is here (AC_MovementManager.cpp):

 void UAC_MovementManager::SetMovementMode(const EMovementEnum& NewValue)
     if (MovementMode == NewValue) return; // It crashes here
     PrevMovementMode = MovementMode;
     MovementMode = NewValue;

Here is the previous stack (LabyrinthCharacter.cpp):

 void ALabyrinthCharacter::OnMovementModeChanged(EMovementMode PrevMovementMode, uint8 PreviousCustomMode)
     Super::OnMovementModeChanged(PrevMovementMode, PreviousCustomMode);
     if (CharacterMovement->MovementMode == MOVE_Walking || CharacterMovement->MovementMode == MOVE_NavWalking) MovementComponent->SetMovementMode(EMovementEnum::MM_Grounded);
     else if (CharacterMovement->MovementMode == MOVE_Falling) MovementComponent->SetMovementMode(EMovementEnum::MM_Falling);

MovementMode is declared as below (AC_MovementManager.h):

 UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "State Values")
         EMovementEnum MovementMode;

and initialized as EMovementEnum::MM_Grounded in UAC_MovementManager() (constructor).

EMovementEnum is declared (and included) in a separate header as following:

 enum class EMovementEnum : uint8
     MM_None UMETA(DisplayName = "None"),
     MM_Grounded UMETA(DisplayName = "Grounded"),
     MM_Falling UMETA(DisplayName = "Falling"),
     MM_Ragdoll UMETA(DisplayName = "Ragdoll")
Product Version: UE 4.20
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asked Aug 28 '18 at 09:30 PM in C++ Programming

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avatar image Shadowriver Aug 28 '18 at 09:55 PM

Move back in call stack and see if "MovementComponent" is not invalid pointer, i case of invalid pointer function may still pass but they may operate on junk data and eventually crash in midway of it

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