What is gcnew?

62
votes

I stumbled across this code and am too proud to go and ask the author what it means.

Hashtable^ tempHash = gcnew Hashtable(iterators_);

IDictionaryEnumerator^ enumerator = tempHash->GetEnumerator();

What is gcnew and how important is it to use that instead of simply new? (I'm also stumped by the caret; I asked about that over here.)

3
.netc++-cli
You can read about some of the C++/CLI features here: en.wikipedia.org/wiki/C%2B%2B/CLI – Mark Ingram
the caret '^' acts like the '' when declaring a managed type ie; std::string str; // pointer to std::string - can be nulptr – user2796283

3 Answers

77
votes

gcnew is for .NET reference objects; objects created with gcnew are automatically garbage-collected; it is important to use gcnew with CLR types

48
votes

gcnew is an operator, just like the new operator, except you don't need to delete anything created with it; it's garbage collected. You use gcnew for creating .Net managed types, and new for creating unmanaged types.

5
votes

The caret '^' acts simarly to the '*' in C/C++ when declaring a type;

// pointer to new std::string object -> memory is not garbage-collected
std::string* strPtr = new std::string;

// pointer to System::String object -> memory is garbage-collected
System::String^ manStr = gcnew System::String;

I use the term 'pointer' when describing the managed object as a managed object can be compared to 'nullptr' just like a pointer in C/C++. A reference in C/C++ can not be compared to 'nullptr' as it is the address of an existing object.

Managed objects use automatic-reference-counting meaning that they are destroyed automatically when they have a reference count of zero although if two or more unreachable objects refer to eachother, you will still have a memory leak. Be warned that automatic reference counting is not free performance wise so use it wisely.