当托管句柄保存在托管容器(IList )中时,是否有必要在C ++ / CLI中使用GC :: KeepAlive?
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我对于何时需要在C ++ / CLI包装器代码中使用KeepAlive以及如何处理生存期感到困惑。请考虑以下代码,并记下我询问是否需要KeepAlive的地方。
// convert from managed to native string
inline std::string ToStdString(String^ source)
{
if (String::IsNullOrEmpty(source))
return std::string();
int len = ((source->Length+1) * 2);
/*** Do I need GC::KeepAlive(source) here? ***/
char *ch = new char[ len ];
bool result ;
{
pin_ptr<const wchar_t> wch = PtrToStringChars( source );
result = wcstombs( ch, wch, len ) != -1;
}
std::string target = ch;
delete ch;
if(!result)
throw gcnew Exception(\"error converting System::String to std::string\");
return target;
}
// convert from native to managed string
inline String^ ToSystemString(const std::string& source)
{
return gcnew String(source.c_str());
}
// unmanaged C++ class
struct NativeDog
{
std::string name;
std::string bark() const {return \"woof\";}
void eat(std::string& food) const {food.clear();}
};
typedef shared_ptr<NativeDog> NativeDogPtr;
// C++/CLI wrapper class
ref class ManagedDog
{
NativeDogPtr* base_;
NativeDog& base() {return **base_;}
ManagedDog() {base_ = new NativeDogPtr(new NativeDog);}
~ManagedDog() {if (base_) delete base_;}
!ManagedDog() {delete this;}
property String^ name
{
String^ get() {return ToSystemString(base().name);}
void set(String^ name)
{
base().name = ToStdString(name);
/*** Do I need GC::KeepAlive(name) here? ***/
}
}
String^ bark() {return ToSystemString(base().bark());}
void eat(String^ food)
{
std::string nativeFood = ToStdString(food);
base().eat(nativeFood);
food = ToSystemString(nativeFood);
/*** Do I need GC::KeepAlive(food) here? ***/
}
};
// unmanaged C++ class
struct NativeKennel
{
vector<NativeDogPtr> dogs;
};
// C++/CLI wrapper class
ref class ManagedKennel
{
NativeKennel* base_;
NativeKennel& base() {return *base_;}
IList<ManagedDog^>^ dogs;
void addDog(ManagedDog^ dog)
{
base().dogs.push_back(*dog->base_);
dogs->Add(dog);
/*** Do I need GC::KeepAlive(dog) here? Will the IList manage the ManagedDog lifetimes? ***/
}
};
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