我目前正在试图获取一个C#委托C++函数指针,我看着example from Microsoft:防止委托
// MarshalDelegate1.cpp
// compile with: /clr
#include <iostream>
using namespace System;
using namespace System::Runtime::InteropServices;
#pragma unmanaged
// Declare an unmanaged function type that takes two int arguments
// Note the use of __stdcall for compatibility with managed code
typedef int (__stdcall *ANSWERCB)(int, int);
int TakesCallback(ANSWERCB fp, int n, int m) {
printf_s("[unmanaged] got callback address, calling it...\n");
return fp(n, m);
}
#pragma managed
public delegate int GetTheAnswerDelegate(int, int);
int GetNumber(int n, int m) {
Console::WriteLine("[managed] callback!");
return n + m;
}
int main() {
GetTheAnswerDelegate^ fp = gcnew GetTheAnswerDelegate(GetNumber);
GCHandle gch = GCHandle::Alloc(fp);
IntPtr ip = Marshal::GetFunctionPointerForDelegate(fp);
ANSWERCB cb = static_cast<ANSWERCB>(ip.ToPointer());
Console::WriteLine("[managed] sending delegate as callback...");
// force garbage collection cycle to prove
// that the delegate doesn't get disposed
GC::Collect();
int answer = TakesCallback(cb, 243, 257);
// release reference to delegate
gch.Free();
}
的调用的GCHandle ::的Alloc()是应该阻止垃圾收集器收集委托。但我的理解是,变量GetTheAnswerDelegate^fp已经使委托保持活着状态,因为它是一个根对象,并且即使当我删除对GCHandle的调用时,该例仍然有效。只有当我内联这样的代表实例:
IntPtr ip = Marshal::GetFunctionPointerForDelegate(gcnew GetTheAnswerDelegate(GetNumber));
然后我看到崩溃。
所以是微软的例子错误还是我错过了什么?
你是完全正确的!即使在调试器中运行发布版本(无GCHandle :: Alloc())也会崩溃。谢谢! – BugSlayer 2013-05-14 13:57:16