checked_delete提升安全性

boost提供了一个安全的用于delete模板函数，在文件checked_delete.hpp中：

[cpp]
template<class T> inline void checked_delete(T * x)
{
    // intentionally complex - simplification causes regressions
    typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
    (void) sizeof(type_must_be_complete);
    delete x;
}
为什么？因为对一个incomplete type的指针运行delete操作结果是未定义的。
什么时候会出现incomplete type的指针，举个例子：

[cpp]
class B;

void Destroy(B* b) {
delete b;
}
如果你不调用这Destroy函数的话，G++不会报错，但是会显示警告：
[cpp]
main.cpp:30:12: warning: possible problem detected in invocation of delete operator: [enabled by default]
main.cpp:29:6: warning: ‘b’ has incomplete type [enabled by default]
main.cpp:27:7: warning: forward declaration of ‘class B’ [enabled by default]
main.cpp:30:12: note: neither the destructor nor the class-specific operator delete will be called, even if they are declared when the class is defined
mkdir -p build/Debug/GNU-Linux-x86
B就是一个incomplete type.
这是个警告，但不是错误，为什么？因为C++标准是允许的，只说结果未定义，各个编译器自己决定吧。

5.3.5/5:

"If the object being deleted has incomplete class type at the point of deletion and the complete class has a non-trivial destructor or a deallocation function, the behavior is undefined."

现在boost用typedef来进行编译期检查。这种typedef .... 在我前面分析boost::bind代码的时候曾经见过。数组不允许长度为-1，而incomplete type会导致这一个编译错误。www.zzzyk.com
因此这是一个在编译复杂的C++代码时非常安全的好工具，只是编译时多花点时间。

同样，还有一个很有用的工具用来安全的delete数组。

[cpp]
template<class T> inline void checked_array_delete(T * x)
{
    typedef char type_must_be_complete[ sizeof(T)? 1: -1 ];
    (void) sizeof(type_must_be_complete);
    delete [] x;
}

补充：综合编程 , 安全编程 ,