8 __gc References
Visual Studio .NET 2003
A __gc reference is similar to a C++ reference, except that the referenced object can be moved during execution by the garbage collector.
Example
// __gc_references.cpp
// compile with: /clr
#using <mscorlib.dll>
__gc class G {
public:
int i;
};
int main() {
G & g = *(new G);
g.i = 10;
System::Console::WriteLine(g.i);
}
Output
10
Characteristics
- The address of a __gc reference is a __gc pointer.
Example
// __gc_references2.cpp
// compile with: /clr
#using <mscorlib.dll>
__value struct G { int i; };
int main() {
G g;
G & v = g;
v.i = 4;
G __gc * p = & g; // __gc is optional
p -> i = 6;
System::Console::WriteLine(v.i);
}
Output
6
Where convenient, __gc references can be used instead of __gc pointers. Every __gc reference abides by all C++ rules for references. The default rules for the __gc and __nogc keywords on references are the same as for pointers: the reference is __gc whenever the modified type is managed.
Example
// __gc_references3.cpp
// compile with: /clr
#using <mscorlib.dll>
__value struct V { int i; };
__gc struct G { int i; };
void f( V & w ) { // __gc reference by default
w.i = 10;
};
void f( G & h ) { // __gc reference by default
h.i = 20;
};
int main() {
V v;
G * pG = new G;
f(v); //call f by reference
System::Console::WriteLine(v.i);
f(*pG); //call the other f by reference
System::Console::WriteLine(pG->i);
}
Output
10 20
