為什么我得到 munmap_chunk(): invalid pointer: error

Question

因此，當我嘗試在 class 字符中的“setweapon”function 中“刪除”先前分配的武器行為時，我正在做一些分配並突然面臨這個“無效指針”錯誤。 有人可以就可能出現的問題給出一些指示嗎？

#include <iostream>
using namespace std;

class WeaponBehaviour{
public:
    virtual void useWeapon() = 0;
};

class SwordBehaviour : public WeaponBehaviour {
public:
    void useWeapon()
    {
        cout << "slash slash"<< endl;
    }
};
class BowAndArrowBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        cout << "suss suss"<< endl;
    }
};

class KnifeBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        cout << "chak chakk"<< endl;
    }
};
class AxeBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        cout << "chop chop"<< endl;
    }
};



class Character{
protected:
    WeaponBehaviour* weaponBehaviour;
public:
    Character(){

    }
    ~Character(){
        if(weaponBehaviour != NULL)
        {
            delete weaponBehaviour;
        }
    }
    void setWeapon(WeaponBehaviour* newWeapon)
    {
        if(weaponBehaviour!= NULL )
            delete weaponBehaviour;

        weaponBehaviour = newWeapon;
    }
    void fight()
    {
        weaponBehaviour->useWeapon();
    }
};

class King : public Character
{
public:
    King(){
        setWeapon(new SwordBehaviour);
    }
};

class Queen : public Character
{
public:
    Queen(){
        setWeapon(new KnifeBehavior);
    }
};

int main() {
    King king ;
    king.fight();
    Queen queen ;
    queen.fight();
    queen.setWeapon(new AxeBehavior);
    queen.fight();
    return 0;
}

我得到的錯誤是

* `Cpp-design-patters/Debug/strategy-pattern' 中的錯誤：munmap_chunk()：無效指針：0x0000000000400f50 * ======= 回溯：========/lib/x86_64-linux -gnu/libc.so.6(+0x777e5)[0x7ff746d757e5] /lib/x86_64-linux-gnu/libc.so.6(cfree+0x1a8)[0x7ff746d82698]

Answer 1

您需要將weaponBehaviour初始化為nullptr否則weaponBehaviour將有一個未定義的（可能是非空的）值和

if(weaponBehaviour!= NULL)
  delete weaponBehaviour;

將通過 if 語句並刪除無效指針。

您的編譯器還應該警告您（如果您已打開警告）您有一個沒有虛擬析構函數的虛擬 class。 當通過WeaponBehaviour指針刪除 object 時，這會導致未定義的行為。 WeaponBehaviour的正確聲明是：

class WeaponBehaviour{
public:
    virtual WeaponBehaviour() {}
    virtual void useWeapon() = 0;
};

它不會在您的代碼中造成問題（還），但您應該了解三/五的規則。

以上所有問題都可以通過使用std::unique_ptr來解決，並使您的代碼更簡單、更安全：

#include <iostream>
#include <memory>

class WeaponBehaviour{
public:
    virtual ~WeaponBehaviour(){}
    virtual void useWeapon() = 0;
};

class SwordBehaviour : public WeaponBehaviour {
public:
    void useWeapon()
    {
        std::cout << "slash slash\n";
    }
};
class BowAndArrowBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        std::cout << "suss suss\n";
    }
};

class KnifeBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        std::cout << "chak chakk\n";
    }
};
class AxeBehavior : public WeaponBehaviour {
public:
    void useWeapon()
    {
        std::cout << "chop chop\n";
    }
};



class Character{
protected:
    std::unique_ptr<WeaponBehaviour> weaponBehaviour;
public:
    void setWeapon(std::unique_ptr<WeaponBehaviour>&& newWeapon)
    {
        weaponBehaviour = std::move(newWeapon);
    }
    void fight()
    {
        weaponBehaviour->useWeapon();
    }
};

class King : public Character
{
public:
    King(){
        setWeapon(std::make_unique<SwordBehaviour>());
    }
};

class Queen : public Character
{
public:
    Queen(){
        setWeapon(std::make_unique<KnifeBehavior>());
    }
};

int main() {
    King king ;
    king.fight();
    Queen queen ;
    queen.fight();
    queen.setWeapon(std::make_unique<AxeBehavior>());
    queen.fight();
    return 0;
}