{"content":{"id":684,"title":"'Build Your Own Lisp' Solutions: 4.7","body":"\u003cp\u003e\u003cb\u003eQ:\u003c/b\u003e What does the preprocessor command \u003ci\u003e#ifndef\u003c/i\u003e do?\u003c/p\u003e\r\n\u003cbr\u003e\r\n\u003cp\u003e\u003cb\u003eA:\u003c/b\u003e Checks if a token has already been defined earlier in the file, or in a previous file, then includes anything between it and \u003ci\u003e#else\u003c/i\u003e or \u003ci\u003e#endif\u003c/i\u003e.\u003c/p\u003e","publication_date":"2019-06-01T00:00:00.000Z","created_at":"2019-05-01T18:38:12.000Z","updated_at":"2019-06-01T02:44:45.000Z","user_id":1,"rating":null},"tags":"\u003ca class=\"changeable-title\" href=\"/q?tag=c\"\u003ec\u003c/a\u003e \u003ca class=\"changeable-title\" href=\"/q?tag=lisp\"\u003elisp\u003c/a\u003e \u003ca class=\"changeable-title\" href=\"/q?tag=build_your_own_lisp\"\u003ebuild_your_own_lisp\u003c/a\u003e \u003ca class=\"changeable-title\" href=\"/q?tag=answers\"\u003eanswers\u003c/a\u003e \u003ca class=\"changeable-title\" href=\"/q?tag=programming\"\u003eprogramming\u003c/a\u003e"}

'Build Your Own Lisp' Solutions: 4.7

Q: What does the preprocessor command #ifndef do?


A: Checks if a token has already been defined earlier in the file, or in a previous file, then includes anything between it and #else or #endif.