C++/CLI (C++ modified for Common Language Infrastructure) is a language specification created by Microsoft and intended to supersede Managed Extensions for C++. It is a complete revision that aims to simplify the older Managed C++ syntax, which is now deprecated. C++/CLI was standardized by Ecma as ECMA-372. It is currently available in Visual Studio 2005, 2008, 2010, 2012, 2013, 2015 and 2017, including the Express editions.
C++/CLI is not mentioned in 'The .NET Language Strategy' by Mads Torgersen, posted February 1, 2017.
C++/CLI should be thought of as a language of its own (with a new set of keywords, for example), instead of the C++ superset-oriented Managed C++ (MC++) (whose non-standard keywords were styled like
__value). Because of this, there are some major syntactic changes, especially related to the elimination of ambiguous identifiers and the addition of .NET-specific features.
Many conflicting syntaxes, such as the multiple versions of operator
new() in MC++, have been split: in C++/CLI, .NET reference types are created with the new keyword
gcnew (i.e. garbage collected new()). Also, C++/CLI has introduced the concept of generics from .NET (similar, for the most common purposes, to standard C++ templates, but quite different in their implementation).
In MC++, there were two different types of pointers:
__nogc pointers were normal C++ pointers, while
__gc pointers worked on .NET reference types. In C++/CLI, however, the only type of pointer is the normal C++ pointer, while the .NET reference types are accessed through a "handle", with the new syntax
ClassName^ (instead of
ClassName*). This new construct is especially helpful when managed and standard C++ code is mixed; it clarifies which objects are under .NET automatic garbage collection and which objects the programmer must remember to explicitly destroy.
A tracking reference in C++/CLI is a handle of a passed-by-reference variable. It is similar in concept to using "
*&" (reference to a pointer) in Standard C++, and (in function declarations) corresponds to the "
ref" keyword applied to types in C#, or "
ByRef" in Visual Basic .NET. C++/CLI uses a "
^%" syntax to indicate a tracking reference to a handle.
The following code shows an example of the use of tracking references. Replacing the tracking reference with a regular handle variable would leave the resulting string array with 10 uninitialized string handles, as only copies of the string handles in the array would be set, due to their being passed by value rather than by reference.
Note that this would be illegal in C#, which does not allow
foreach loops to pass values by reference. Hence, a workaround would be required.
Another change in C++/CLI is the introduction of the finalizer syntax
!ClassName(), a special type of nondeterministic destructor that is run as a part of the garbage collection routine. The C++ destructor syntax
~ClassName() also exists for managed objects, and better reflects the "traditional" C++ semantics of deterministic destruction (that is, destructors that can be called by user code with
In the raw .NET paradigm, the nondeterministic destruction model overrides the protected
Finalize method of the root
Object class, while the deterministic model is implemented through the
IDisposable interface method
Dispose (which the C++/CLI compiler turns the destructor into). Objects from C# or VB.NET code that override the Dispose method can be disposed of manually in C++/CLI with
delete just as .NET classes in C++/CLI can.
Operator overloading works analogously to standard C++. Every * becomes a ^, every & becomes an %, but the rest of the syntax is unchanged, except for an important addition: for .NET classes, operator overloading is possible not only for classes themselves, but also for references to those classes. This feature is necessary to give a ref class the semantics for operator overloading expected from .NET ref classes. (In reverse, this also means that for .NET framework ref classes, reference operator overloading often is implicitly implemented in C++/CLI.)
For example, comparing two distinct String references (String^) via the operator == will give true whenever the two strings are equal. The operator overloading is static, however. Thus, casting to Object^ will remove the overloading semantics.