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TURBO PASCAL 5.5: ANSWERS TO COMMON QUESTIONS --------------------------------------------- 1. Can I build programs bigger than 64K? The total size of a program's code is only limited by the memory you have available; but each unit (module) can be no larger than 64K, since it has to have its own code segment. The data segment is still no more than 64K, but the heap is unlimited just as in 3.0. In fact, we've rewritten the heap manager to make it much more efficient. There's no waste when allocating memory (in 3.0, all blocks were rounded up to a factor of 8), and you can install a heap error routine that gets called if an allocation request fails. All in all, 5.5's heap manager is much faster than version 3.0. 2. Can Turbo Pascal run on generic MS-DOS machines? TPC.EXE will run on generic machines when you use the /Q option. The System, Overlay, Dos, and Printer standard units will operate correctly on MS-DOS generic machines. Generated .EXE's are MS-DOS compatible as long as you don't use the special PC units (such as Crt, Graph, and Graph3). 3. Does Turbo Pascal 5.5 support large integers? Yes, TP 5.5 has virtually every incarnation of 8-, 16-, and 32-bit integers: shortint, integer, longint, byte, and word. 4. Will the toolboxes for 4.0 work with 5.5? Yes, all 4.0 versions of the toolboxes will work with Turbo Pascal 5.5. In a few cases, minor changes to compiler directives are recommended. Refer to the Turbo Pascal README file for more information. 5. Does Turbo Pascal version 5.5 support conditional compilation? Yes, Turbo 5.5 includes conditional compilation support. You use {$DEFINE ...} and {$UNDEF ...} for symbols and {$IFDEF ...}. Using the {$IFOPT ...} conditional directive, you can even test the settings of compiler directives like R-, N+, and others. For the command-line compiler, you can define symbols with the /D directive. In the integrated compiler, you can also define symbols via the Options/Compiler/Conditional Defines menu command. 6. How much of the 64K in the data segment is actually available to my program? The amount of data segment used by the run-time library depends on which standard units you use in your program. Here is the data segment usage (in bytes) for each unit: UNIT Data Size ---- --------- System 664 Overlay 24 Crt 20 Dos 6 Printer 256 Graph 1070 Turbo3 256 Graph3 0 ========= 2282 The total size of the data segment is 65,520 bytes. If you used only the System unit, the amount of data segment space left over would be 65520 - 664 = 64856 bytes 7. What is the largest global data structure you can allocate? The maximum size of a single variable that can be allocated on the heap is 65,521 bytes. 8. How do I find out how much code and data were generated by the compiler for a program or unit? If you are using the integrated environment, build your program or unit and then use the Get Info command in the Compile menu. This will bring up a window of information that includes the size of code and data. If you are using the command-line compiler, the size of generated code and data is displayed on the screen at the end of compilation. 9. Are the .OBJ files generated by Turbo C and Turbo Assembler compatible with 5.5? You can write Turbo C or Turbo Assembler routines and link the .OBJ files into your Turbo Pascal programs by using {$L} compiler directives. Turbo Pascal 5.5 generates .TPU (Turbo Pascal Unit) files, not .OBJ files. We've made that decision for many reasons: A. TP 5.5's .TPU files are smaller than .OBJ's, and they contain symbolic information important to the support of Pascal's strict type conventions (types, constants, etc.). B. .TPU files allow "smart linking" - elimination of unused code and data on a procedure-by-procedure basis. C. .TPU's allow built-in project management through version 5.5's Make and Build commands. D. .TPU's allow faster compilation speeds (34,000 lines per minute on a PS/2 Model 60). 10. Will the $L compiler directive work for compiler object files other than assembler? That depends on the language. TURBO requires all the code in the .OBJ to be in *one* CODE segment, and all the data to be in *one* DATA segment. With assembly language that's easy, but it may not work with some high-level language compilers. You can use Turbo C to generate .OBJ files for use by Turbo Pascal programs. An example, CPASDEMO.PAS is included on the distribution disks. 11. Does the built-in linker eliminate unused data? Yes. Unused code AND data are stripped when you compile to disk. 12. If two units use a third unit, does the third unit get included twice in my program? No. All your units are "linked" together when you compile your program. Only one copy of each procedure and function used is generated. There is NO duplication of run-time code. In fact, Turbo Pascal 5.5 has "smart linking," which eliminates any unused code and data from the final .EXE. 13. What happens if you attempt to link another unit in which the compiler directives are set differently? Compiler directives are local to the unit they are declared in. Thus, the compiler directives in one unit, or in the main program, have no effect on the directives set in another unit. 14. Can I create my own .TPL file? Yes, but Turbo Pascal will only use the TURBO.TPL library file. If you want to add your own units to the TURBO.TPL file, you can use the unit mover program (TPUMOVER.EXE). For example, you might want a customized version of TURBO.TPL for each of the programs you're developing. A corresponding configuration file for Turbo Pascal would specify a different Turbo directory and thus fetch the appropriate .TPL file for each of your projects. 15. What rules should I follow when writing an interrupt handler? The following is a list of rules to keep in mind when writing an interrupt handler: A. Use GetIntVec and SetIntVec to install/uninstall interrupt handlers B. Use the interrupt directive C. Be careful about reentrancy. Don't use any calls to DOS or to Turbo Pascal's overlay or heap management routines in your interrupt handler D. Interrupt procedures and functions must use the far call model (use the {$F+} option) E. Be proficient with the BIOS and assembly language before attempting to write an interrupt handler F. Make sure your interrupt handler is not in an overlaid unit. G. Neither static nor virtual methods can be used as interrupt handlers. 16. Does a procedure or function in a program have to be of a near or far call model? If you are using overlays or procedural variables, you should probably turn {$F+} on for all units and the main program (the extra overhead of always using far calls is usually quite small). Otherwise, Turbo Pascal automatically selects the correct call model. A routine is always a near call model unless 1) It is declared in the interface section of a unit 2) You override the default call model by using the {$F+} compiler option 3) It is an object method. Methods are always far calls. You should also use the {$F+} option to override the default call model if you are writing interrupt handlers, error handlers, exit procedures, or procedures or functions that will be called via a procedural variable. 17. How do I write reentrant code in Turbo Pascal? If a routine follows these rules, it is reentrant: A. All data is allocated on the stack. B. The routine doesn't use any global variables. C. The routine can be interrupted at any time without affecting the execution of the routine. D. The routine doesn't call any other routines that are not reentrant (e.g., DOS I/O). 18. What is the best approach to taking advantage of the new IEEE floating-point types? The new IEEE floating-point types are available when you compile your program with {$N+} and you have a math coprocessor; they are also available if you don't have a coprocessor, but specify {N+,E+}. The 8087 emulator has greater precision, but is significantly slower than the fast, 6-byte, software-only reals. When developing programs that will be compiled and run on machines without the 8087 coprocessor, consider the trade-offs of speed (built-in reals) vs. precision (8087 hardware/emulation) and make the appropriate choice. 19. What type is Comp? What is it useful for? The Comp type is a cross between an integer and a real type and is available when 8087 code is generated {$N+}. If no math coprocessor is available, specify {$N+,E+} and the emulator will support the Comp type. The compiler treats it as a real type without an exponent. Thus Comp is useful when you need to store extremely large numbers but don't need a decimal point. For example, you might use variables of type Comp to store amounts in cents and divide the value of the variable by 100 to determine what the value in dollars and cents would be. 20. How many significant digits do the 8087 floating-point types provide? Type Digits of precision -------- ------------------- single 7-8 double 15-16 extended 19-20 comp 19-20 21. Are the intermediate results of real number expressions stored in the 8087 registers? No. The user (8086) stack is used to store intermediate results of real number expressions. 22. How does rounding work with IEEE floating point? The 8087 math coprocessor uses a different method for rounding numbers than what you may be used to. In order to achieve a more even distribution of values, the 8087 uses a method sometimes called "Banker's Rounding." This method dictates that a number will always be rounded to the nearest EVEN number. Note that this is quite different than always rounding UP. Here are a couple of examples: Round(0.5) = 0 Round(1.5) = 2 23. How do you do I/O redirection? If you want to do DOS I/O redirection when running an .EXE file generated by Turbo Pascal, DON'T use the Crt unit. If you do, make sure you assign a null file name to the standard Output file handle: Assign(Output, ''); { Assign a null file name Output } ReWrite(Output); { Open the file for output } Any Write statement that does not specify a file variable will be redirected to the DOS standard output file. 24. How do you go about upgrading version 3.0 programs with lots of chain files? Chaining is not possible with .EXE files. Control can be passed to another program by use of the EXEC procedure in the DOS unit. You can also use 5.5's overlay manager to build very large programs. 25. Are overlays supported in 5.5? Yes! See the example program OVRDEMO.PAS and refer to the Turbo Pascal manual for information on overlays. 26. Is there any support in Turbo Pascal 5.5 for file and record locking? There's a standard variable in the System unit called FileMode, which you can use to assign an open mode for use in all subsequent Resets. There are no record-locking routines implemented in the standard version, but they are easily implemented through MsDos calls. 27. Does Turbo 5.5 support procedural parameters? Yes. See PROCVAR.PAS, DIRDEMO.PAS, and refer to the Reference Guide for a complete description. 28. Can you use identifiers other than scalar in the case statement? Case statements allow the following ordinal types: Char, Boolean, ShortInt, Byte, Integer, Word, and user-defined enumeration. 29. Is the run-time license policy the same as in version 3.0? YES, there are no royalties! 30. C has static variables, is there anything similar in 5.5? You can declare private global variables in the implementation part of a unit. Such variables are only visible within that unit. Like other globals, they retain their values across calls. Typed constant declarations declared within a procedure or function also behave exactly like C's static variables. They are local in scope but since they are allocated in the data segment, they retain their values from call to call. 31. What Turbo Pascal 3.0 code will cause the most problems converting to version 5.5? With our UPGRADE program (see appropriate Appendix in your manual), it's not very difficult to port your code to 5.5. It depends a lot on the type of programs you write. The passing of parameters on the stack is done much more efficiently now, so changes will have to be made to inline machine code and assembly language. Most of the changes are optional: using new types, breaking your program into modules to take advantage of separate compilation. (The UPGRADE program has a special option to help you "unitize" your program too. It does all the "typing" for you.) Some stricter type-checking is performed in version 5.5. For example, the Dos unit now defines the often-seen registers record type (AX, BX...); MsDos and Intr now take this type. In this case, you can type-cast or change the type identifier and recompile. 32. What books can I read that will help me with Turbo Pascal 5.5? The Turbo Pascal Tutor is an excellent reference to Turbo Pascal. Also, Osborne/McGraw Hill has a line of books about Borland's products. 33. How do I use .BIN files provided by third-party vendors with 5.5? We've included a utility on your distribution disk called BINOBJ.EXE, which converts binary files into .OBJ files that are linkable to your Turbo Pascal 5.5 programs. In general this will only work if the binary files contain data, not code. Contact your third-party vendor to see if they also provide .OBJ versions of their programs. 34. Why does TURBO sometimes try to read from another drive when I run it? When you leave Turbo Pascal, it saves the name and path of the file you were last editing in a pick list. The next time you load Turbo, it checks this pick list and tries to load the file you were last editing. If the file you were last editing was in another drive, Turbo will try to read from that drive. This also occurs if you have installed another drive as your Turbo Directory. 35. Does Turbo Pascal 5.5 support EMS? Yes, Turbo Pascal 5.5 will use up to 64K of EMS for storing the edit buffer. In addition, you can instruct the Overlay unit to place your overlaid units in EMS. Finally, EMS.PAS on the distribution disk shows you how to access EMS memory from a Turbo Pascal program. 36. How can I allocate my own I/O buffer for a text file? You can use the procedure SetTextBuf to allocate your own text file buffer either in the data segment or on the heap. 37. Why aren't the new settings used after I install TURBO.EXE using the TINST.EXE program? You probably have a .TP file in the current or Turbo directory being loaded and the settings in the .TP file override the settings installed by TINST. Delete the .TP file. 38. What is the largest string supported? A string can be 255 characters long. You can write your own routines to handle strings with lengths greater than 255 characters. 39. Can I still write to file 'Con' without changes? The 'Con' file is no longer supported, but you can still write to the screen with a simple Write with no file variable. The file system has been completely redesigned to allow you to write your own text file device drivers. With these, you can implement a Pascal-like text-file interface to any device, such as serial ports, windowing systems, memory, etc. 40. What is constant merging? For example, when you use the same string constant more than once in a program block, the compiler only saves one copy of this string. In the generated program, a pointer is created that references the one copy of this string in the generated .EXE file. 41. Have Turbo Pascal 3.0 run-time error codes changed in Turbo Pascal 5.5? Yes, error codes have changed; refer to Appendix I in the Reference Guide. The Turbo3 unit contains a version 3.0 compatible IOResult function.