通用內存分配崩潰過度編碼新的和刪除在C + +

Question

我有以下代碼。當我刪除分配的內存時，下面的代碼崩潰了，即Rational :: deleteMemPool（）;

獲取輸出

內存池值是00000000內存池值是003462E8內存池值003462E8

//這裏刪除崩潰，雖然我們有有效的指針。

任何人都可以幫助我什麼是bug？

#include <string> 
#include <iostream> 


template < class T > 
class MemoryPool { 
public: 
    MemoryPool (size_t size = EXPANSION_SIZE); 
    ~MemoryPool(); 
    inline void* alloc (size_t size); // Allocate a T element from the free list. 
    inline void free (void *someElement); // Return a T element to the free list. 
private: 
    MemoryPool<T> *next; // next element on the free list. 
    enum { EXPANSION_SIZE = 32}; // If the freeList is empty, expand it by this amount. 
    void expandTheFreeList(int howMany = EXPANSION_SIZE); // Add free elements to the free list 
}; 

template < class T > MemoryPool <T> :: MemoryPool (size_t size) { 
    expandTheFreeList(size); 
} 

template < class T > MemoryPool <T> :: ~MemoryPool() { 
    MemoryPool<T> *nextPtr = next; 
    for (nextPtr = next; nextPtr != NULL; nextPtr = next) { 
     next = next->next; 
     delete [] nextPtr; 
    } 
} 

template < class T > inline void* MemoryPool <T> :: alloc (size_t) { 
    if (!next) { 
     expandTheFreeList(); 
    } 

    MemoryPool<T> *head = next; 
    next = head->next; 
    return head; 
} 

template < class T > inline void MemoryPool <T> :: free (void *doomed) { 

    MemoryPool<T> *head = static_cast <MemoryPool<T> *> (doomed); 
    head->next = next; 
    next = head; 
} 

template < class T > void MemoryPool <T> :: expandTheFreeList(int howMany) { 
    // We must allocate an object large enough to contain the next pointer. 
    size_t size = (sizeof(T) > sizeof(MemoryPool<T> *)) ? sizeof(T) : sizeof(MemoryPool<T> *); 
    void *pNewAlloc = new char[size]; 
    MemoryPool<T> *runner = static_cast <MemoryPool<T> *> (pNewAlloc); 
    next = runner; 
    for (int i = 0; i < howMany ; i++) { 
     void *pNewAlloc = new char[size]; 
     runner->next = static_cast <MemoryPool<T> *> (pNewAlloc); 
     runner = runner->next; 
    } 
    runner->next = 0; 
} 

class Rational { 
public: 
    Rational (int a = 0, int b = 1) : n(a), d(b) {} 
    void *operator new(size_t size) { return memPool->alloc(size); } 
    void operator delete(void *doomed,size_t size) { memPool->free(doomed); } 

    static void newMemPool() { 
     std::cout << "mempool value is " << Rational::memPool << std::endl; 
     memPool = new MemoryPool <Rational>; 
     std::cout << "mempool value is " << Rational::memPool << std::endl; 
    } 
    static void deleteMemPool() { 
     std::cout << "mempool value is " << Rational::memPool << std::endl; 
     delete memPool; 
    } 

private: 
    int n; // Numerator 
    int d; // Denominator 
    static MemoryPool <Rational> *memPool; 
}; 

MemoryPool <Rational> *Rational::memPool = 0; 
int main() { 

    Rational *array[1000]; 

    Rational::newMemPool(); 


    // Start timing here 
    for (int j = 0; j < 1; j++) { 
     for (int i = 0; i < 10; i++) { 
      array[i] = new Rational(i); 
     } 

     for (int i = 0; i < 10; i++) { 
      delete array[i]; 
     } 
    } 

    // Stop timing here 
    Rational::deleteMemPool(); 

} 

堆棧跟蹤：

Stack trace:> 
ReadParsing.exe!Rational::deleteMemPool() Line 75 C++ 
ReadParsing.exe!main() Line 107 C++ 
ReadParsing.exe!__tmainCRTStartup() Line 586 + 0x19 bytes C 
ReadParsing.exe!mainCRTStartup() Line 403 C 
kernel32.dll!7c817077() 

Answer 1

你有你如何在你的記憶池中刪除塊有問題。當您分配塊時，您在expandTheFreeList(i)中使用new char[size]。

但是，當你刪除那些塊，您使用delete [] nextPtr：

template < class T > MemoryPool <T> :: ~MemoryPool() { 
    MemoryPool<T> *nextPtr = next; 
    for (nextPtr = next; nextPtr != NULL; nextPtr = next) { 
     next = next->next; 
     delete [] nextPtr;  // <-- problem 
    } 
} 

而且由於nextPtr是一個memoryPool<T>*，你釋放了錯誤的事情（和它結束了遞歸到這個destrcutor啓動）。

改變這個問題行：

delete [] reinterpret_cast<char*>(nextPtr); 

似乎使事情不會崩潰。當然，可能還有其他問題。