{"id":25920,"date":"2022-02-13T21:05:19","date_gmt":"2022-02-13T14:05:19","guid":{"rendered":"https:\/\/tom.ji42.com\/?p=25920"},"modified":"2022-02-13T21:05:19","modified_gmt":"2022-02-13T14:05:19","slug":"empty-function-vfox","status":"publish","type":"post","link":"https:\/\/tom.tomwork.net\/?p=25920","title":{"rendered":"EMPTY( ) Function – VFOX"},"content":{"rendered":"
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Visual FoxPro 9.0 Language Reference<\/span><\/td>\n<\/tr>\n
EMPTY( ) Function<\/span><\/td>\n<\/tr>\n
See Also\u00a0<\/a>\u0412\u00a0\u00a0Example<\/a>\u0412<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\n\n
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<\/div>\n

Determines whether an expression evaluates to empty.<\/p>\n

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<\/th>\n<\/tr>\n
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EMPTY(eExpression<\/i>)<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Parameters<\/h4>\n
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eExpression<\/i><\/dt>\n<\/dl>\n
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Specifies the expression that\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0evaluates. You can specify an expression with\u00a0Character<\/b>,\u00a0Numeric<\/b>,\u00a0Date<\/b>,\u00a0Varbinary<\/b>,\u00a0Blob<\/b>, or\u00a0Logical<\/b>\u00a0type, or the name of a\u00a0Memo<\/b>\u00a0or\u00a0General<\/b>\u00a0field in an open table.<\/dd>\n<\/dl>\n<\/div>\n
Return Value<\/span><\/h1>\n
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Logical.\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0returns True (.T.) if the expression\u00a0eExpression<\/i>\u00a0evaluates to empty; otherwise,\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0returns False (.F.).<\/p>\n
When expression types evaluate to the values in the following table,\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0returns True (.T.).<\/p>\n
<\/h3>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Expression type<\/th>\nEvaluates to<\/th>\n<\/tr>\n
Blob<\/b><\/td>\nEmpty (0h) or contains only zero bytes, for example, 0h00, 0h000000, and so on<\/td>\n<\/tr>\n
Character<\/b><\/td>\nEmpty string, spaces, tabs, carriage returns, linefeeds, or any combination of these<\/td>\n<\/tr>\n
Currency<\/b><\/td>\n0<\/td>\n<\/tr>\n
Date<\/b><\/td>\nEmpty, for example, CTOD(”)<\/td>\n<\/tr>\n
DateTime<\/b><\/td>\nEmpty, for example, CTOT(”)<\/td>\n<\/tr>\n
Double<\/b><\/td>\n0<\/td>\n<\/tr>\n
Float<\/b><\/td>\n0<\/td>\n<\/tr>\n
General<\/b><\/td>\nEmpty (no OLE object)<\/td>\n<\/tr>\n
Integer<\/b><\/td>\n0<\/td>\n<\/tr>\n
Logical<\/b><\/td>\nFalse (.F.)<\/td>\n<\/tr>\n
Memo<\/b><\/td>\nEmpty (no contents)<\/td>\n<\/tr>\n
Numeric<\/b><\/td>\n0<\/td>\n<\/tr>\n
Varbinary<\/b><\/td>\nEmpty (0h) or contains only zero bytes, for example, 0h00, 0h000000, and so on<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
Remarks<\/span><\/h1>\n
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You cannot use\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0to determine whether a variable object reference is empty. For example, a variable can contain an object reference for a form. If the form is closed by clicking Close from the form’s pop-up menu or by issuing\u00a0CLEAR WINDOWS<\/b>, the variable contains the null value.<\/p>\n
The following program example demonstrates how to use\u00a0TYPE(\u0412\u00a0)<\/b>\u00a0and\u00a0ISNULL(\u0412\u00a0)<\/b>\u00a0to determine if a variable object reference is valid.<\/p>\n
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\u0412<\/th>\nCopy Code<\/span><\/th>\n<\/tr>\n
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goMyForm = CREATEOBJECT('Form')\r\nWAIT WINDOW IIF(TYPE('goMyForm') = 'O' AND !ISNULL(goMyForm), ;\r\n   'goMyForm has valid object reference',;\r\n   'goMyForm does not have valid object reference')<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
Example<\/span><\/h1>\n
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The following example opens the\u00a0customer<\/code>\u00a0table in the\u00a0testdata<\/code>\u00a0database.\u00a0FOR … ENDFOR<\/b>\u00a0is used to create a loop in which\u00a0EMPTY(\u0412\u00a0)<\/b>\u00a0s used to determine if\u00a0TAG(\u0412\u00a0)<\/b>\u00a0returns the empty string. The name of each structural index tag is displayed with its candidate status.<\/p>\n
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\u0412<\/th>\nCopy Code<\/span><\/th>\n<\/tr>\n
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CLOSE DATABASES\r\nOPEN DATABASE (HOME(2) + 'data\\testdata')\r\nUSE customer     && Open customer table\r\n\r\nFOR nCount = 1 TO TAGCOUNT( )\r\n   IF !EMPTY(TAG(nCount))  && Checks for empty string\r\n   ? TAG(nCount)  && Display tag name\r\n   ? CANDIDATE(nCount)  && Display candidate status\r\n   ELSE\r\n      EXIT  && Exit the loop when no more tags are found\r\n   ENDIF\r\nENDFOR<\/pre>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
See Also<\/span><\/h1>\n
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Other Resources<\/h4>\n
Functions<\/a>
\nLEN( ) Function<\/a>
\nTYPE(\u0412\u00a0) Function<\/a>
\nISNULL(\u0412\u00a0) Function<\/a><\/p>\n<\/div>\n<\/div>\n
Send\u00a0comments<\/a>\u00a0about this topic to Microsoft. \u0412\u00a9 Microsoft Corporation. All rights reserved.<\/div>\n<\/div>\n
 <\/p>\n","protected":false},"excerpt":{"rendered":"
Visual FoxPro 9.0 Language Reference EMPTY( ) Function See Also\u00a0\u0412\u00a0\u00a0Example\u0412 Determines whether an expression evaluates to empty. EMPTY(eExpression)<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[13],"tags":[],"class_list":["post-25920","post","type-post","status-publish","format-standard","hentry","category-13"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p6cOVM-6K4","_links":{"self":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/25920","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=25920"}],"version-history":[{"count":1,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/25920\/revisions"}],"predecessor-version":[{"id":25921,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/25920\/revisions\/25921"}],"wp:attachment":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=25920"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=25920"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=25920"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}