Question

在我的程序中，我使用全局变量alloc_ptr first_alloc = NULL;，并使用结构和函数进行内存管理：

typedef struct alloc_struct
{
    void* ptr;
    struct alloc_struct* prev;
} *alloc_ptr;

void *alloc(unsigned long size)
{
    alloc_ptr tmp = new struct alloc_struct;
    tmp->ptr = new char[size];
    tmp->prev = first_alloc;
    first_alloc = tmp;
    return tmp->ptr;
}

void free_one(void* ptr)
{
    alloc_ptr tmp = first_alloc;
    alloc_ptr tmp2 = tmp;
    while(tmp != NULL)
    {
        if(ptr == tmp->ptr)
        {
            delete[] tmp->ptr;
            if(tmp == first_alloc)
            {
                first_alloc = tmp->prev;
            }
            else
            {
                tmp2->prev = tmp->prev;
            }
            delete tmp;
            break;
        }
        tmp2 = tmp;
        tmp = tmp->prev;
    }
}

void free_all()
{
    alloc_ptr tmp;
    while (first_alloc != NULL)
    {
        delete[] first_alloc->ptr;
        tmp = first_alloc->prev;
        delete first_alloc;
        first_alloc = tmp;
    }
    first_alloc = NULL;
}

我使用valgrind尝试了我的程序，并在函数Mismatched free() / delete / delete []和free_one中收到了很多错误free_all。如果我更改delete和delete[]则无效。这有什么问题？

感谢您的任何建议。

Answer 1

尝试使用g ++ 6.3.0，编译器会生成以下内容要求两行分配/释放ptr：

tmp->ptr = new char[size];
=> _Znam which is operator new[](unsigned long)/__builtin_vec_new

delete[] tmp->ptr;
=> _ZdlPv which is operator delete(void*)/__builtin_delete

所以，Valgrind抱怨似乎是正确的。

g ++还会发出警告，例如：

warning: deleting ‘void*’ is undefined [-Wdelete-incomplete]
             delete[] tmp->ptr;

因此，您的代码是未定义的行为，编译器可以做任何事情，并且已经决定生成触发valgrind错误的东西。

C ++ - valgrind - 不匹配的free（）/ delete / delete []

1 个答案: