Once upon a time, x. Base wasnt a programming language, it. Users of x. Base tools. Fox. Base, d. Base, and similar tools to manage their data. Base. was steadily improved and finally developed into a full blown programming. Fox. Pro became a professional development environment which reached. Fox. Pro 2. 52. 6. Almost ten years ago in 1. A procedural programming language became an object. Visual Fox. Pro is not just an object oriented environment. Delphi or Visual Basic. NET. Visual Fox. Pro still contains its roots. Just. try to run a Turbo Pascal 3. Delphi 7. 0. What about your GW BASIC. Visual Basic. NET But Foxbase Till today you can run code. Visual Fox. Pro that you have written in the eighties. Screen output. doesnt look as nice, but you can still run code in VFP 8 almost 2. Visual Fox. Pro is almost fully backward compatible. Thinking. about it this means that a good deal of the code in Fox. Pro and Fox. Base is still. Select. Doc Page 1 82696 The Basics of Querying in FoxPro with SQL SELECT Lesson I Single Table Queries The idea behind a query is to take a large database. Visual Fox. Pro. This means that object orientation sits on top of. Fox. Pro, and not vice versa. Many strange behaviors of Visual Fox. Pro only become. explainable if you think how you would have done something in Fox. Base, only to. realize that Visual Fox. Pro doesnt do it any different. One warning in advance The following articles tries to. Visual Fox. Pro works internally. The actual internals of Fox. Pro are. the intellectual property of Microsoft and are not publicly disclosed. Everyone. who really knows how Visual Fox. Pro works inside is prohibited to talk about. Non Disclosure Agreement NDA. Ive collected the following. Some information are in the MSDN. Library that Microsoft publishes quarterly some articles only exist in older. MSDN Library. Other information come from sample code that. Microsoft ships. Most pieces, however, come from tests and observation, not. Especially. differences in the behavior of various versions allow to make conclusions on. VFP. Some of the following structures have been extended. Fox. Pro. The Name Table Index NTIIn Visual Fox. Objectoriented programming OOP is a programming paradigm based on the concept of objects, which may contain data, in the form of fields, often known as. Once upon a time, xBase wasnt a programming language, it was a tool to automatically retrieve and manipulate data. Users of xBase tools werent primarily developers. Pro we can name various items. To those items. Visual Fox. Pro assigns something called a name. These items are variables. Each of these elements has got a label and a. The visibility scope of a variable, for instance, depends on its type. A field name must be unique. Whenever you create a variable, open a table, and so on. Visual Fox. Pro creates a new entry in an internal list, the Name Table. The position inside this list is the Name Table Index or NTI for short. In this list, every name is assigned a unique number between 1 and 6. Theres just a single global list. This is why you can only create up to 6. Since aliases and. Visual Fox. Pro 6. The management of this list has been optimized in the. Fox. Pro. When you release a name by closing a table or. Visual Fox. Pro doesnt remove the. It only marks the entry as invalid, just like it does with. Items are finally removed by a process called Garbage. Cmigration%5Cwhitepapers/vfp_rgk.GIF' alt='How To Create A Simple Program In Foxpro Game' title='How To Create A Simple Program In Foxpro Game' />Collection. This term refers to the process of removing invalid entries in. Visual Fox. Pro. executes the garbage collection in its idle loop. This loop is entered. Visual Fox. Pro is in a waiting condition caused by READ, READ EVENTS. INKEY, or WAIT WINDOW. This is still true if you use the command with the. You can use this trick to force Visual Fox. How To Create A Simple Program In Foxpro SoundsPro to. WAIT WINDOW NOWAIT. It wasnt until Visual Fox. Pro 7. 0 that SYS1. Code Visual to Flowchart is an automatic program Flow chart generator, it supports most programming languages and Visio,Word,Excel,PowerPoint,PNG and BMP output formats. Taming the Visual FoxPro report preview window How to improve the way your VFP reports appear on the screen. When you preview a report in Visual FoxPro, the output. Fox. Pro 2. 6. at least. SYS1. 10. 4 manually triggers a garbage collection. Its not the same. Visual Fox. Pro does more. Windows. messages. During program execution, Visual Fox. Pro is not in an idle loop and. Until Visual Fox. Pro 5. 0 this. had the effect that more and more entries in the name table have been marked as. This had far reaching consequences on performance, but also. Every time a new entry is added to the name table, Visual Fox. Pro. has to search all existing entries to find conflicting names. For variables. this means to check if a new variable with a lower scope already exist, because. PUBLIC variable when a LOCAL variable of the. For aliases this means to verify that the alias name is not in. This search process caused exponential. While you could measure the creation of the first object. Visual Fox. Pro already minutes to. Application that never reach an idle state like import. Some. functions, too, demanded a new entry in the name table, like the REQUERY. The slow down wasnt the only problem. The. closer an application came to the limit, the more instable it became. If you. were lucky, Visual Fox. Pro issued a too many names error, but. Visual Fox. Pro 6. When. the number of items in the name table approaches the 9. Visual Fox. Pro. automatically initiates a garbage collection. In a program that creates 6. A major improvement came in Visual Fox. Pro 7. 0. All previous. When you create two labels. LOCAL lo. Label. 1, lo. Label. 2lo. Label. Create. ObjectLabello. Label. 2 Create. ObjectLabelVisual Fox. Pro adjusts the name property. The first label is. Label. 1, for the second label Label. Name results in. Label. To make this happen, Visual Fox. Pro registered each object. The consequence is that each object creation takes longer. You can bypass this to a certain degree by assigning a. Informix Update Statistics Drop Distribution Database. SYS2. 01. 5 in the Init event. Nonetheless, this behavior limits. In Visual Fox. Pro 3. When that limit has been reached, you cant even open the. Form Designer as it also tries to create objects. Visual Fox. Pro 7. CREATEOBJECT or NEWOBJECT, nor do they. Therefore you can create far more than. Visual Fox. Pro 6. The disadvantage. A small price to pay. Variables, Arrays and Objects. One of the most frequently asked questions that developers. Visual Fox. Pro can only manage up to 6. The answer is a definite. NO. One array counts as a single variable, no matter how many elements it. Because the number of elements is limited to 6. Even in Visual Fox. Pro. you can stores masses of data in memory. Due to performance reasons no real. The reason for all of. Actually, Visual Fox. Pro only. knows to deal, with variables simple variables, that is. The support of. arrays, and later objects, has been fitted into this design. But what is a variable in Visual Fox. Pro Variables in Fox. Pro. can store values of any data type. However, as Visual Fox. Pro is written in C. Fox. Pro variables, as well, have to be stored in a C format at some. Visual Fox. Pro stores variables in a C structure. Even though the. following structure comes from the Library Construction Kit, its probably close. Visual Fox. Pro uses internally, if not even identical typedef struct   char        evtype  char        evpadding  short        evwidth  unsigned    evlength  long        evlong  double      evreal  CCY         evcurrency  MHandle      evhandle  unsigned long evobject Value In addition to the type, theres an entry for each supported. Visual Fox. Pro uses different fields depending on which data type. The structure explains why strings can contain any characters. Visual Fox. Pro deals with. The actual string and objects are not stored directly in. To access strings, Visual Fox. Pro. uses a so called memory handle which will be explained in just a moment. Objects are identified using a not closer documented 3. It might. surprise that arrays are not mentioned at all. Every time a program creates a new memory variable, Visual. Fox. Pro allocates a memory block with the above structure. Its address has to be. Saving these information is the job of the name table. Every entry in the name. The list is limited.