Pointers and release build in Visual Studio

问题

I have a weird problem when I create a release build with Visual Studio 2008. I was wondering if one of you could help me understand what is going on.

Description: I have a class member function which returns a pointer to a structure stored in the class:

const MyStruct * Myclass::getPointer() { 
    return mystruct_variable; // this is properly initialyzed 
}

One another point worth pointing out is that this class/method is in a dll, and I export it to use in a separate executable project. When I make a release build and try to use the above mentioned method, the run crashes depending on if the getPointer() method is inlined (i.e. placed in the header file part of the class) or not (placed in the cpp file).

The usage is:

const MyStruct * cf = myclassObj.getPointer();
int n = cf->size_t;
std::cout<<n<<std::endl;

When MyClass::getPointer() is inlined in the header the assembly looks like:

const MyStruct * cf = myclassObj.getPointer();
  012514A8  mov         esi,dword ptr [ebx+794h] 
int n =cf->size_t;
  012514AE  mov         eax,dword ptr [esi+20h] 
std::cout<<n<<std::endl;
  012514B1  mov         ecx,dword ptr [__imp_std::endl (1252038h)] 
  012514B7  push        ecx  
  012514B8  mov         ecx,dword ptr [__imp_std::cout (125203Ch)] 
  012514BE  push        eax  
  012514BF  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (1252048h)] 
  012514C5  mov         ecx,eax 
  012514C7  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (1252044h)] 

The same code when the class method for getPointer() is not inlined, and placed in the corresponding cpp file gives:

const MyStruct * cf = myclassObj.getPointer();
  00DA14A8  mov         ecx,ebx 
  00DA14AA  call        dword ptr [__imp_MyClass::getPointer(0DA2104h)] 
int n =cf->size_t;
std::cout<<n<<std::endl;
  00DA14B0  mov         ecx,dword ptr [__imp_std::endl (0DA2038h)] 
  00DA14B6  mov         esi,eax 
  00DA14B8  mov         eax,dword ptr [esi+20h] 
  00DA14BB  push        ecx  
  00DA14BC  mov         ecx,dword ptr [__imp_std::cout (0DA203Ch)] 
  00DA14C2  push        eax  
  00DA14C3  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (0DA2048h)] 
  00DA14C9  mov         ecx,eax 
 00DA14CB  call        dword ptr [__imp_std::basic_ostream<char,std::char_traits<char> >::operator<< (0DA2044h)] 

Any thoughts why the two cases have different assembly set? Am I doing something wrong? Thanks!

回答1:

If you link against a C++ DLL you must make sure all the compiler flags are exactly the same. Otherwise the size of structures, virtual tables etc. might be different and the code fails with an invalid access to memory. Inlining of course overcomes this as the code is inside the exe file, not in the dll, and thus compiled with the correct flags.

Simply put - for a release build use release DLL, for a debug build use debug DLL.

来源：https://stackoverflow.com/questions/11592775/pointers-and-release-build-in-visual-studio