What is gcnew?

Question

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.)

You can read about some of the C++/CLI features here: http://en.wikipedia.org/wiki/C%2B%2B/CLI — Mark Ingram, Oct 14 '08 at 19:24
the caret '^' acts like the '*' when declaring a managed type ie; std::string* str; // pointer to std::string - can be nulptr — user2796283, Apr 26 '16 at 10:37

score 76 · Accepted Answer · edited Oct 14 '08 at 19:26

76

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

edited Oct 14 '08 at 19:26

Chris Jester-Young

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answered Oct 14 '08 at 19:18

Steven A. Lowe

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@[Chris Jester-Young]: Thanks Chris, that's good to know how to fix the MS links – Steven A. Lowe Oct 14 '08 at 19:53
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Out of curiosity, how important is it to use `gcnew` with CLR types? Is it okay to statically declare a CLR type (ie use `System::String` instead of `System::String^`)? Will it correctly deallocate at the end of its lifetime/scope? – jliv902 Dec 01 '14 at 19:05
@jliv902: I doubt it - but I've been out of that sphere for a while! – Steven A. Lowe Dec 01 '14 at 23:08

Joel Coehoorn · Answer 2 · 2020-10-01T18:55:07.317

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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.

edited Oct 01 '20 at 18:55

answered Oct 14 '08 at 19:19

Joel Coehoorn

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upvoted (not that you need the points) because we posted the same answer at the same time – Steven A. Lowe Oct 15 '08 at 15:43

score 5 · Answer 3 · answered Apr 26 '16 at 11:04

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.

What is gcnew?

3 Answers3

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