这篇文章会有点大,所以提前抱歉。无论如何,在调试模式(Visual Studio 2010)下运行我的程序时出现异常,我不太明白为什么会发生:
Unhandled exception at 0x5524ad4a (msvcp100d.dll) in CppTest1.exe: 0xC0000005: Access violation reading location 0xfeeefef2.
我对 C++ 很陌生,我正在尝试实现一个类似 pimpl 的模式类结构,如下所示:
声明.h
#include <vector>
class A
{
public:
struct aStruct
{
std::string aString;
std::vector<std::string> moreStrings;
};
A();
~A();
void addSomething(aStruct thing);
private:
class Implementation;
Implementation* instance;
};
class B
{
public:
B();
~B();
void doWork();
private:
class Implementation;
Implementation* instance;
};
class A::Implementation
{
public:
Implementation();
~Implementation();
void addSomething(aStruct thing);
private:
std::vector<A::aStruct> bunchOfStructs;
};
class B::Implementation
{
public:
Implementation();
~Implementation();
void doWork();
private:
A member;
};
主文件
#include "declaration.h"
A::A() : instance(new Implementation) {}
A::~A() { delete instance; }
void A::addSomething(aStruct thing) { instance->addSomething(thing);}
A::Implementation::Implementation() {}
A::Implementation::~Implementation() {}
void A::Implementation::addSomething(aStruct thing) { bunchOfStructs.push_back(thing);}
B::B() : instance(new Implementation) {}
B::~B() {delete instance;}
B::Implementation::Implementation() { doWork();}
B::Implementation::~Implementation() {}
void B::Implementation::doWork()
{
A a;
member = a;
}
int main( int argc, char* argv[] )
{
B b;
return 0;
}
现在,当代码转义主块时,会调用 B 的析构函数,这反过来又会删除 Implementation,后者又会调用其持有的 Implementation 实例的析构函数,依此类推,直到 A 的实例中持有的向量 bundleOfStructs 的析构函数叫做。这就是失败的地方。
调用堆栈如下所示:
msvcp100d.dll!std::_Container_base12::_Orphan_all() Line 201 + 0x12 bytes C++
CppTest1.exe!std::vector<A::aStruct,std::allocator<A::aStruct> >::_Tidy() Line 1304 + 0xb bytes C++
CppTest1.exe!std::vector<A::aStruct,std::allocator<A::aStruct> >::~vector<A::aStruct,std::allocator<A::aStruct> >() Line 706 C++
CppTest1.exe!A::Implementation::~Implementation() Line 8 + 0x2b bytes C++
CppTest1.exe!A::Implementation::`scalar deleting destructor'() + 0x2b bytes C++
CppTest1.exe!A::~A() Line 4 + 0x50 bytes C++
CppTest1.exe!B::Implementation::~Implementation() Line 14 + 0x2b bytes C++
CppTest1.exe!B::Implementation::`scalar deleting destructor'() + 0x2b bytes C++
CppTest1.exe!B::~B() Line 12 + 0x50 bytes C++
CppTest1.exe!main(int argc, char * * argv) Line 24 + 0x12 bytes C++
据我了解 0xfeeefeee 是调试期间 Visual Studio 中使用的填充模式。异常消息表明我正在尝试访问已经删除的内容?但我不太明白为什么会这样。在我认为之前,某些东西显然已经被破坏了。如果不是因为分配member = a
,代码将运行。此外,如果我在没有模式的情况下实现它,它似乎运行良好。例如:
这个工程.h
#include <vector>
class C
{
public:
struct aStruct
{
std::string aString;
std::vector<std::string> moreStrings;
};
C();
~C();
void addSomething(aStruct thing);
private:
std::vector<C::aStruct> bunchOfStructs;
};
class D
{
public:
D();
~D();
void doWork();
private:
C member;
};
主文件
#include "thisworks.h"
C::C() {}
C::~C() {}
void C::addSomething(aStruct thing) { bunchOfStructs.push_back(thing); }
D::D() { doWork(); }
D::~D() {}
void D::doWork()
{
C c;
member = c;
}
int main( int argc, char* argv[] )
{
D d;
return 0;
}
现在我意识到可能有更好的方法可以做到这一点,但是因为我仍在尝试学习 C++,而且我已经投入了一些时间试图弄清楚为什么这是一个问题,我真的很想了解问题。