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