c++ - 调整C++类的动态数组的大小

我需要调整m_Array的大小，这就是说添加11时valgrind中的问题。element m_Max = 10 m_Len = 10
我被允许使用cstdio，cstdlib，cstring和iostream。

/* m_Len is length of array and m_Max is maximal length */
resizing in CAccount::NewAccount

if ( m_Len >= m_Max )
{
     if (m_Max == 0) m_Max = 5;
     m_Max *= 2;
     CAccount * tmp = new CAccount[m_Max];
     memcpy ( tmp, m_Array, m_Len * sizeof(CAccount));
     delete[] m_Array;
     m_Array = tmp;
}
m_Array[m_Len] = x;
m_Len++;

这是与此相关的附加代码：

CAccount
{
 public:
  ~CAccount ( void )
  {
    delete[] m_Trans;
  }
private:
 struct Transaction
 {
   int a;
   const char * b;
   const char * c;
 }
Transaction * m_Trans;


}


CAccount * m_Array;

这就是valgrind所说的

我的喊话...

==2458== Invalid read of size 4
==2458==    at 0x8048D67: CAccount::AddTransaction(int const&, char const*, char const*) (bank_test.cpp:121)
==2458==    by 0x8049645: CBank::Transaction(char const*, char const*, int, char const*) (bank_test.cpp:268)
==2458==    by 0x8049946: main (bank_test.cpp:327)
==2458==  Address 0x434b150 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==
==2458== Invalid free() / delete / delete[] / realloc()
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048D9A: CAccount::AddTransaction(int const&, char const*, char const*) (bank_test.cpp:121)
==2458==    by 0x8049645: CBank::Transaction(char const*, char const*, int, char const*) (bank_test.cpp:268)
==2458==    by 0x8049946: main (bank_test.cpp:327)
==2458==  Address 0x434b150 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==
==2458== Invalid read of size 4
==2458==    at 0x8048D67: CAccount::AddTransaction(int const&, char const*, char const*) (bank_test.cpp:121)
==2458==    by 0x8049678: CBank::Transaction(char const*, char const*, int, char const*) (bank_test.cpp:269)
==2458==    by 0x8049946: main (bank_test.cpp:327)
==2458==  Address 0x434b188 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==
==2458== Invalid free() / delete / delete[] / realloc()
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048D9A: CAccount::AddTransaction(int const&, char const*, char const*) (bank_test.cpp:121)
==2458==    by 0x8049678: CBank::Transaction(char const*, char const*, int, char const*) (bank_test.cpp:269)
==2458==    by 0x8049946: main (bank_test.cpp:327)
==2458==  Address 0x434b188 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==

然后写另一个提示，然后说

==2458== Invalid read of size 4
==2458==    at 0x8048AD7: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804922E: CBank::~CBank() (bank_test.cpp:224)
==2458==    by 0x80499F0: main (bank_test.cpp:381)
==2458==  Address 0x434b348 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==
==2458== Invalid free() / delete / delete[] / realloc()
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804922E: CBank::~CBank() (bank_test.cpp:224)
==2458==    by 0x80499F0: main (bank_test.cpp:381)
==2458==  Address 0x434b348 is 0 bytes inside a block of size 4 free'd
==2458==    at 0x402B598: operator delete[](void*) (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==2458==    by 0x8048B0A: CAccount::~CAccount() (bank_test.cpp:92)
==2458==    by 0x804951E: CBank::NewAccount(char const*, int) (bank_test.cpp:254)
==2458==    by 0x804991B: main (bank_test.cpp:323)
==2458==
==2458==
==2458== HEAP SUMMARY:
==2458==     in use at exit: 0 bytes in 0 blocks
==2458==   total heap usage: 17 allocs, 27 frees, 1,268 bytes allocated
==2458==
==2458== All heap blocks were freed -- no leaks are possible
==2458==
==2458== For counts of detected and suppressed errors, rerun with: -v
==2458== ERROR SUMMARY: 20 errors from 6 contexts (suppressed: 0 from 0)

最佳答案

这是发生了什么：

CAccount * tmp = new CAccount[m_Max];

您创建了20个新对象CAccount。

memcpy ( tmp, m_Array, m_Len * sizeof(CAccount));

您将10个旧对象的内容存储到了新数组中。

问题是，由于仅使用memcpy而不使用复制构造函数来处理数据的所有权，因此对象的新旧版本都指向相同的m_Trans数据。

调用delete[] m_Array;后，将调用旧对象上的析构函数，它们将删除m_Trans

delete[] m_Trans;

现在，新对象指向已删除的m_Trans数据，因此访问指针将导致未定义的行为。

解决此问题的最干净方法是使用而不是

memcpy ( tmp, m_Array, m_Len * sizeof(CAccount));

做

std::copy(m_Array, m_Array + m_Len, tmp)

这将在新对象上调用opreator =，因此您也需要正确进行设置：

CAccount
{
public:
  CAccount::CAccount(const CAccount& account)
  : m_trans(<initialisation code here>)
{
  <Copy the data from the account>
}

该解决方案是最干净的，但次优，因为您正在复制数据，您可以只切换数据的所有者，但是如果您不追求性能，那就更好。