Null object: Difference between revisions

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 =={{header|C++}}==
-C++'s access to null is (as in C) by way of a macro which simply evaluates to 0.
+In C++ non-pointer types do not support null. (C++ provides value semantics rather than reference semantics). When using pointers C++ permits checking for null by comparing the pointer to a literal of 0, or (as in C) by way of a macro (NULL) which simply expands to 0.
 <lang cpp>#include <iostream>
 #include <cstdlib>
-if (object == NULL) {
+if (object == 0) {
    std::cout << "object is null";
 }</lang>
+boost::optional is available for cases where the programmer wishes to pass by value, but still support a null value.
+<lang cpp>
+#include <boost/optional.hpp>
+#include <iostream>
+boost::optional<int> maybeInt()
+int main()
+{
+  boost::optional<int> maybe = maybeInt();
+  if(!maybe)
+    std::cout << "object is null\n";
+}
+</lang>
 =={{header|C sharp|C#}}==
 As with Java, any reference type may be null, and testing for nullity uses ordinary boolean operators.