{"id":24117,"date":"2020-10-03T07:43:18","date_gmt":"2020-10-03T00:43:18","guid":{"rendered":"https:\/\/tom.ji42.com\/?p=24117"},"modified":"2020-10-03T07:43:18","modified_gmt":"2020-10-03T00:43:18","slug":"procedures-vs-functions","status":"publish","type":"post","link":"https:\/\/tom.tomwork.net\/?p=24117","title":{"rendered":"Procedures Vs Functions"},"content":{"rendered":"

In\u00a0Visual Foxpro<\/a>, you can declare procedural routines or\u00a0Object Oriented<\/a>\u00a0methods as either “PROCEDURE” or “FUNCTION”, and it has no impact on how that routine is handled by VFP, like this:<\/code><\/p>\n

PROCEDURE ThisIsMyProcedure\r\n  Messagebox( \"You are in a Procedure.\" )\r\nENDPROC\r\n\r\nFUNCTION ThisIsMyFunction\r\n  Messagebox( \"You are in a Function.\" )\r\nENDFUNC<\/pre>\n
<\/p>\n
\n
Differences between calling Procedures and Calling Functions<\/h2>\n
Functions return a result, Procedures do Not<\/h3>\n
If a routine does not include a RETURN statement to return a result, it will return .T. by default.<\/p>\n
The calling pattern determines whether a routine is a Procedure or a Function, not its “definition”<\/h3>\n
Even if your routine is defined as a PROCEDURE, you can still call it like a function, and it *is* a function. If you did not include a RETURN statement, the function will return .T. (as mentioned above). (Object Oriented<\/a>\u00a0methods must always be called “as functions”.)<\/p>\n
As discussed in\u00a0Parameters By Value Or Reference<\/a>, the way that you call a procedural routine also determines the handling of the parameters. This can be confusing, even with the information in the previously mentioned article.<\/p>\n
Here are your two options:
\n1) Use “DO … WITH” to call a routine and it will be considered a “procedure”.<\/b>
\nParameters will be passed “by reference” unless they are surrounded by parentheses, and there is no way to “explicitly” pass parameters “by reference”.
\n(Note that\u00a0Set UDFParms<\/a>\u00a0does NOT affect routines called by “DO … WITH”)<\/p>\n
For example:<\/code><\/p>\n
DO MyRoutine WITH ParamByRef, (ParamByValue)\r\nDO MyRoutine WITH @ThisDoesNotWork<\/pre>\n
or<\/p>\n
2) Omit “DO” and “WITH”, and surround all parameters in one pair of parentheses, and your routine will be considered a “function”.<\/b>
\nParameters will be passed “by value” unless:
\nA) You place an “@” in front of the parameter, or
\nB) You place (additional) parentheses around the parameter<\/p>\n
For example:<\/code><\/p>\n
SET UDFPARMS TO VALUE\r\nResult = MyRoutine( ParamByVal, @ParamByRef, (otherParamByVal) )\r\nMyRoutine( ParamByVal, @ParamByRef, (otherParamByVal) )\r\nSET UDFPARMS TO REFERENCE\r\nResult = MyRoutine( ParamByRef, @OtherParamByRef, (ParamByVal) )\r\nMyRoutine( ParamByRef, @OtherParamByRef, (ParamByVal) )<\/pre>\n
Contributors:\u00a0wgcs<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"
In\u00a0Visual Foxpro, you can declare procedural routines or\u00a0Object Oriented\u00a0methods as either “PROCEDURE” or “FUNCTION”, and it has no impact on how that routine is handled by VFP, like this: PROCEDURE ThisIsMyProcedure Messagebox( “You are in a Procedure.” ) ENDPROC FUNCTION ThisIsMyFunction Messagebox( “You are in a Function.” ) ENDFUNC<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_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}},"categories":[13],"tags":[],"class_list":["post-24117","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-6gZ","_links":{"self":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/24117","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=24117"}],"version-history":[{"count":1,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/24117\/revisions"}],"predecessor-version":[{"id":24118,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=\/wp\/v2\/posts\/24117\/revisions\/24118"}],"wp:attachment":[{"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=24117"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=24117"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/tom.tomwork.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=24117"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}