我需要调整 m_Array 的大小,它说在添加 11 时在 valgrind 中出现问题。元素 m_Max = 10 m_Len = 10 我可以使用 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++;
这里是涉及到的附加代码:
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 friend ...
==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==
然后它写了另一个 couts 然后它说这个
==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
是这样的:
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 CAccount 的内容 memcpy 到新数组。
问题是,由于您只使用了 memcpy 而没有处理数据所有权的复制构造函数,对象的新旧版本都指向相同的 m_Trans
数据。
一旦调用 delete[] m_Array;
,旧对象的析构函数就会被调用,它们会删除 m_Trans
删除[] m_Trans;
现在新对象指向已被删除的 m_Trans
数据,因此访问指针将导致未定义的行为。
解决这个问题最干净的方法是使用
memcpy ( tmp, m_Array, m_Len * sizeof(CAccount));
做
std::copy(m_Array, m_Array + m_Len, tmp)
这会在新对象上调用 opreator=,因此您也需要正确地进行设置:
CAccount
{
public:
CAccount::CAccount(const CAccount& account)
: m_trans(<initialisation code here>)
{
<Copy the data from the account>
}
这个解决方案是最干净但不是最理想的,因为您正在复制数据,您可以只切换数据的所有者,但如果您不追求性能,这会更好。
关于c++ - 调整 C++ 类动态数组的大小,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23033331/