Null object: Difference between revisions
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(Move BASIC and part of ActionScript to Undefined values.) |
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trace("object is null");</lang> |
trace("object is null");</lang> |
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ActionScript also has |
ActionScript also has an '''undefined''' value: see [[Undefined values#ActionScript]]. |
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<lang actionscript>var foo; // untyped |
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var bar:*; // explicitly untyped |
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trace(foo + ", " + bar); // outputs "undefined, undefined" |
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if (foo == undefined) |
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trace("foo is undefined"); // outputs "foo is undefined"</lang> |
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=={{header|Ada}}== |
=={{header|Ada}}== |
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Ada.Text_Io.Put_line("object is null"); |
Ada.Text_Io.Put_line("object is null"); |
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end if;</lang> |
end if;</lang> |
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=={{header|ALGOL 68}}== |
=={{header|ALGOL 68}}== |
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In ALGOL 68 the NIL yields a name that does not refer to any value. NIL can never be |
In ALGOL 68 the NIL yields a name that does not refer to any value. NIL can never be |
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display dialog "x is null" |
display dialog "x is null" |
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end if</lang> |
end if</lang> |
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=={{header|AutoHotkey}}== |
=={{header|AutoHotkey}}== |
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<lang AutoHotkey>If (object == null) |
<lang AutoHotkey>If (object == null) |
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MsgBox, object is null</lang> |
MsgBox, object is null</lang> |
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=={{header|BASIC}}== |
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Classic BASIC does have the concept of un-initialised or undefined variables. |
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=={{header|C}}== |
=={{header|C}}== |
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C has the null pointer, written as "0", whose internal representation is often, [http://c-faq.com/null/varieties.html though not always], the same as integer zero. It is (supposedly) garanteed to be pointing to nothing, so receiving one of those likely means you are not looking at an object--<i>but</i>, there are occasions where changing content of a null pointer actually does something (say, on DOS); and a function that's supposed to return a pointer on success doesn't always return a 0 otherwise (e.g. mmap returns -1 for failure). |
C has the null pointer, written as "0", whose internal representation is often, [http://c-faq.com/null/varieties.html though not always], the same as integer zero. It is (supposedly) garanteed to be pointing to nothing, so receiving one of those likely means you are not looking at an object--<i>but</i>, there are occasions where changing content of a null pointer actually does something (say, on DOS); and a function that's supposed to return a pointer on success doesn't always return a 0 otherwise (e.g. mmap returns -1 for failure). |
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