How to: Use Tracking References and Value Types
The following sample shows simple boxing through a tracking reference to a value type:
Example
// tracking_reference_valuetypes_1.cpp
// compile with: /clr
using namespace System;
int main() {
int i = 10;
int % j = i;
Object ^ o = j; // j is implicitly boxed and assigned to o
}
The following sample shows you can have both tracking references and native references to value types.
// tracking_reference_valuetypes_2.cpp
// compile with: /clr
using namespace System;
int main() {
int i = 10;
int & j = i;
int % k = j;
i++; // 11
j++; // 12
k++; // 13
Console::WriteLine(i);
Console::WriteLine(j);
Console::WriteLine(k);
}
13 13 13
The following sample shows that tracking references can be used with value types and native types.
// tracking_reference_valuetypes_3.cpp
// compile with: /clr
value struct G {
int i;
};
struct H {
int i;
};
int main() {
G g;
G % v = g;
v.i = 4;
System::Console::WriteLine(v.i);
System::Console::WriteLine(g.i);
H h;
H % w = h;
w.i = 5;
System::Console::WriteLine(w.i);
System::Console::WriteLine(h.i);
}
4 4 5 5
The following sample shows that you can bind a tracking reference to a value type on the garbage-collected heap.
// tracking_reference_valuetypes_4.cpp
// compile with: /clr
using namespace System;
value struct V {
int i;
};
void Test(V^ hV) { // hv boxes another copy of original V on GC heap
Console::WriteLine("Boxed new copy V: {0}", hV->i);
}
int main() {
V v; // V on the stack
v.i = 1;
V ^hV1 = v; // v is boxed and assigned to hV1
v.i = 2;
V % trV = *hV1; // trV is bound to boxed v, the v on the gc heap.
Console::WriteLine("Original V: {0}, Tracking reference to boxed V: {1}", v.i, trV.i);
V ^hV2 = trV; // hv2 boxes another copy of boxed v on the GC heap
hV2->i = 3;
Console::WriteLine("Tracking reference to boxed V: {0}", hV2->i);
Test(trV);
v.i = 4;
V ^% trhV = hV1; // creates tracking reference to boxed type handle
Console::WriteLine("Original V: {0}, Reference to handle of originally boxed V: {1}", v.i, trhV->i);
}
Original V: 2, Tracking reference to boxed V: 1 Tracking reference to boxed V: 3 Boxed new copy V: 1 Original V: 4, Reference to handle of originally boxed V: 1