C 在结构上调用free会引发运行时错误
我基于创建了一个简单的对象系统。然后,我决定通过添加一个函数来扩充代码,以便在怪物死亡时释放所有关于它的内存:C 在结构上调用free会引发运行时错误,c,struct,function-pointers,free,C,Struct,Function Pointers,Free,我基于创建了一个简单的对象系统。然后,我决定通过添加一个函数来扩充代码,以便在怪物死亡时释放所有关于它的内存: void Monster_destroy(void *self) { Monster* monster=self; if(&(monster->proto)) free(&(monster->proto)); free(monster); } 我在这里使用的函数如下: int Monster_attack(void*
void Monster_destroy(void *self)
{
Monster* monster=self;
if(&(monster->proto))
free(&(monster->proto));
free(monster);
}
我在这里使用的函数如下:
int Monster_attack(void* self,int damage)
{
Monster* monster=self;
char* desc=monster->proto.description;
printf("You attack %s!\n", desc);
monster->hit_points-=damage;
if(monster->hit_points>0)
{
printf("It is still alive\n");
return 0;
}
else
{
printf("It is dead\n");
monster->proto.destroy(monster);
return 1;
}
}
struct Monster
{
Object proto;
int hit_points;
};
typedef struct Monster Monster;
typedef struct
{
char *description;
int (*init)(void *self);
void (*describe)(void* self);
void (*destroy)(void* self);
void* (*move)(void* self,Direction direction);
int (*attack)(void* self,int damage);
}Object;
void Monster_destroy(void *self)
{
Monster* monster = self;
if(&(monster->proto) != NULL)
free(&(monster->proto));
monster->proto = NULL;//Important
}
我得到以下错误:
==4699== Invalid free() / delete / delete[] / realloc()
==4699== at 0x4C2B83A: free (vg_replace_malloc.c:468)
==4699== by 0x40080F: Monster_destroy (ex19.c:15)
==4699== by 0x400A2C: Room_attack (ex19.c:96)
==4699== by 0x400ACA: Map_attack (ex19.c:118)
==4699== by 0x400E20: process_input (ex19.c:175)
==4699== by 0x400F52: main (ex19.c:211)
==4699== Address 0x51fd500 is 0 bytes inside a block of size 56 free'd
==4699== at 0x4C2B83A: free (vg_replace_malloc.c:468)
==4699== by 0x400803: Monster_destroy (ex19.c:14)
==4699== by 0x400A2C: Room_attack (ex19.c:96)
==4699== by 0x400ACA: Map_attack (ex19.c:118)
==4699== by 0x400E20: process_input (ex19.c:175)
==4699== by 0x400F52: main (ex19.c:211)
==4699==
我有一个怪物看起来像这样的系统:
int Monster_attack(void* self,int damage)
{
Monster* monster=self;
char* desc=monster->proto.description;
printf("You attack %s!\n", desc);
monster->hit_points-=damage;
if(monster->hit_points>0)
{
printf("It is still alive\n");
return 0;
}
else
{
printf("It is dead\n");
monster->proto.destroy(monster);
return 1;
}
}
struct Monster
{
Object proto;
int hit_points;
};
typedef struct Monster Monster;
typedef struct
{
char *description;
int (*init)(void *self);
void (*describe)(void* self);
void (*destroy)(void* self);
void* (*move)(void* self,Direction direction);
int (*attack)(void* self,int damage);
}Object;
void Monster_destroy(void *self)
{
Monster* monster = self;
if(&(monster->proto) != NULL)
free(&(monster->proto));
monster->proto = NULL;//Important
}
对象
是一个如下所示的结构:
int Monster_attack(void* self,int damage)
{
Monster* monster=self;
char* desc=monster->proto.description;
printf("You attack %s!\n", desc);
monster->hit_points-=damage;
if(monster->hit_points>0)
{
printf("It is still alive\n");
return 0;
}
else
{
printf("It is dead\n");
monster->proto.destroy(monster);
return 1;
}
}
struct Monster
{
Object proto;
int hit_points;
};
typedef struct Monster Monster;
typedef struct
{
char *description;
int (*init)(void *self);
void (*describe)(void* self);
void (*destroy)(void* self);
void* (*move)(void* self,Direction direction);
int (*attack)(void* self,int damage);
}Object;
void Monster_destroy(void *self)
{
Monster* monster = self;
if(&(monster->proto) != NULL)
free(&(monster->proto));
monster->proto = NULL;//Important
}
这就是我现在使用“怪物”的方式:
if(monster && monster->hit_points>0)
{
monster->proto.attack(monster,damage);
return 1;
}
else
{
//dont even call Monster_attack because Monster has no hit_points
printf("You flail at the air and hit nothing,Idiot\n");
if(monster)
monster->proto.destroy(monster);
return 0;
}
在
struct Monster
中,proto
不是动态分配的,因此您不必释放它
尝试不使用以下行:
if(&(monster->proto))
free(&(monster->proto));
在函数Monster\u destroy
中
请记住,只有在指针上使用过
malloc()
时,才在指针上使用free()
。在struct Monster
中,proto是对象
不是对象*
所以在Monster\u destroy()
函数中这样释放内存是无效的
if(&(monster->proto))
free(&(monster->proto));
事实上,您没有专门为proto
分配内存,因此不需要释放它
但是,如果为
proto->description
分配了内存,则需要使用free(proto->description)
释放内存。我认为应该这样编写:
int Monster_attack(void* self,int damage)
{
Monster* monster=self;
char* desc=monster->proto.description;
printf("You attack %s!\n", desc);
monster->hit_points-=damage;
if(monster->hit_points>0)
{
printf("It is still alive\n");
return 0;
}
else
{
printf("It is dead\n");
monster->proto.destroy(monster);
return 1;
}
}
struct Monster
{
Object proto;
int hit_points;
};
typedef struct Monster Monster;
typedef struct
{
char *description;
int (*init)(void *self);
void (*describe)(void* self);
void (*destroy)(void* self);
void* (*move)(void* self,Direction direction);
int (*attack)(void* self,int damage);
}Object;
void Monster_destroy(void *self)
{
Monster* monster = self;
if(&(monster->proto) != NULL)
free(&(monster->proto));
monster->proto = NULL;//Important
}
上次对monster变量执行的释放是无用的(充其量),因为您正在将一个地址传递到堆栈中(当函数返回该地址时,会通过将sp寄存器移回自动删除该地址)
您应该只在动态分配的内存上使用free,就像您使用“malloc”或“new”创建的内存一样。当您声明变量时,它们从系统堆栈获得内存。但当您声明指针并为它们分配内存时,它是从堆中分配的。这就是为什么您可以使用从堆(动态)分配的
free()
释放内存。但是您不能尝试使用free删除堆栈中分配的内存。我认为最后这个free(monster)是没有用的,因为它只是堆栈上的一个指针(您没有在堆上分配它)。虽然您发布的代码的答案听起来是正确的,我想指出一个事实,Valgrind显示的调用堆栈与怪物攻击
无关,尽管存在房间攻击
。你确定你有正确的函数吗?哦,等等,我把Monster_destroy的调用从Monster_攻击改为Room_攻击,因为我想看看它是否在那里工作。因为proto
不是动态分配的,所以你不能对它使用free()
。因此,您的代码是错误的。在释放description
后,如何将proto
设置为NULL
,正如上面的一个答案所述,当从类型“void*”分配给类型“Object”时,它会给我不兼容的类型。