类静态指针的申请和释放

如果类有一个静态成员指针变量，在进程中执行new或malloc操作分配了内存，进程退出前并不需要调用new或malloc，因为系统会自动进行释放。但这个静态成员指针变量需要多少分配，又应该如果处理呢，最近在项目代码中看到这样的例子，和大家分享一下。

#include <unistd.h>
#include <stdio.h>

class CPointer
{
public:
CPointer(){};
~CPointer(){};
public:
static char * m_p;
};

char * CPointer::m_p = NULL;

void proc()
{
for(int i = 0; i < 10; i++)
{
CPointer::m_p = new char[1024*1024];
sleep(1);
}
}

int main(int argc, char ** argv)
{
proc();
return 0;
}

用valgrind执行，会发现内存泄漏，如下所示，当然，这是很显然的，多次new但没有delete。

valgrind --tool=memcheck --leak-check=full ./a.out

==3893== LEAK SUMMARY:
==3893== definitely lost: 5,242,880 bytes in 5 blocks.
==3893== possibly lost: 4,194,304 bytes in 4 blocks.
==3893== still reachable: 1,048,576 bytes in 1 blocks.
==3893== suppressed: 0 bytes in 0 blocks.
==3893== Reachable blocks (those to which a pointer was found) are not shown.
==3893== To see them, rerun with: --show-reachable=yes

那应该如何解决呢，当然是应该delete，但是类的静态成员在类的生命周期中是不能delete的，感兴趣的朋友可以试下，进程会core。

但是可以把静态指针赋给另一个局部指针，把局部指针释放掉，这样，即保存了静态指针，同时，资源也得释放。修改代码如下：

#include <unistd.h>
#include <stdio.h>

class CPointer
{
public:
CPointer(){};
~CPointer(){};
public:
static char * m_p;
};

char * CPointer::m_p = NULL;

void proc()
{
for(int i = 0; i < 10; i++)
{
if (NULL != CPointer::m_p)
{
char * p = CPointer::m_p;
delete []p;
p = NULL;
CPointer::m_p = NULL;
}
CPointer::m_p = new char[1024*1024];
sleep(1);
}
}

int main(int argc, char ** argv)
{
proc();
return 0;
}

再用valgrind执行，问题解决。

==3912== LEAK SUMMARY:
==3912== definitely lost: 0 bytes in 0 blocks.
==3912== possibly lost: 0 bytes in 0 blocks.
==3912== still reachable: 1,048,576 bytes in 1 blocks.
==3912== suppressed: 0 bytes in 0 blocks.
==3912== Reachable blocks (those to which a pointer was found) are not shown.
==3912== To see them, rerun with: --show-reachable=yes