HDevelop User's Manual

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84 CHAPTER 4. CODE GENERATION One of these messages is always returned indicating the status of the operator. Normally, the result is À ÅË ÌÊÍ. Some operators return À ÅË ÁÄ like Ö Ñ or Ö ÖÓÒ to indicate that they could not open a file or there was no permission to read it. In this case the programmer has to check the return value and apply some adequate action. If the message À ÅË ÄË is ignored, errors like ÀÐÓÒ ÖÖÓÖ ¼ ÁÑ Ø ÑÒÑÒØ ÓØ¹Á × ÆÍÄÄ will happen in successive operators, because the predecessor operator did not calculate an appropriate value. Errors In the case of hard errors (i.e., no message as described above) the program stops with an error message. To prevent this behavior the HDevelop operators Ú ÖÖÓÖ ÚÖ and Ú ×Ø can be used to control the exception handling in the application. This works similarly in HDevelop and C++. One difference is caused by the dynamic evaluation of Ú ÖÖÓÖ ÚÖ in HDevelop. This means that each time the operator is executed (e.g., in a loop) the use of the error variable might change. In contrast to this, in C++ special code is added to store the return values of operators. This code will therefore be static and cannot change during program excecution. To understand how the code generation works let us have a look at a short example. Here at first the HDevelop program: Ú×Ø´³ÚÖÖÓÖ³µ ÚÖÖÓÖÚÖ´ÖÖÓÖ¸ØÖÙµ ØÖ×ÓÐ´Ñ¸ÖÓÒ¸½¼¼¸¾µ ÚÖÖÓÖÚÖ´ÖÖÓÖ¸Ð×µ ´ÖÖÓÖ ÀÅËÌÊÍµ ÛÖØ×ØÖÒ´ÏÒÓÛÁ¸³ÖÖÓÖ ÒÙÑÖ ³ · ÖÖÓÖµ ÜØ´µ Ò Ú×Ø´³ÚÖÖÓÖ³µ This program will be translated into ÀÌÙÔÐ ÖÖÓÖ ×Ø´ÚÖÖÓÖµ ÖÖÓÖ ØÖ×ÓÐ´Ñ¸²ÖÓÒ¸½¼¼¸¾µ ´ÖÖÓÖ ¾µ ß ÛÖØ×ØÖÒ´ÏÒÓÛÁ¸ÀÌÙÔÐ´ÖÖÓÖ ÒÙÑÖ µ · ÀÌÙÔÐ´ÖÖÓÖµµ ÜØ´½µ Ð ×Ø´ÚÖÖÓÖµ As can be seen, the operator Ú ÖÖÓÖ ÚÖ is eliminated and replaced by the use of the error variable later on. The points mentioned above might cause these two problems: ¯ If the second parameter of Ú ÖÖÓÖ ÚÖ cannot be derived from the program (because no constant Ð× or ØÖÙ are used but expressions, the value will be interpreted as ØÖÙ, HDevelop / 2000-11-16
4.1. CODE GENERATION FOR C++ 85 that means: “start to use the variable”. To avoid confusion use only the constants Ð× or ØÖÙ as values for the second parameter. ¯ The usage of a variable starts after the first call of Ú ÖÖÓÖ ÚÖ´ÖÖÎÖÐ¸ØÖÙµ. In C++ this means that all successive lines (i.e., lines “below”), until the first Ú ÖÖÓÖ ÚÖ´ÖÖÎÖÐ¸Ð×µ will have the assignment to ÖÖÎÖÐ. This might lead to a different behavior compared with HDevelop, if Ú ÖÖÓÖ ÚÖ is called inside a loop, because here the operators inside the loop before Ú ÖÖÓÖ ÚÖ might also use ÖÖÎÖÐ after the second excecution of the loop body. Therefore: Try not to use Ú ÖÖÓÖ ÚÖ inside a loop. Use it right at the beginning of the program. 4.1.4.2 Compiler errors Sometimes it happens that messages like º»ÜÑÔÐºÔÔ¸ ÐÒ ½ ÓÔÖÒ× ÓÖ ÒØ ÀÌÙÔÐ or º»ÜÑÔÐºÔÔ¸ ÐÒ ½ ÖÖÓÖ ÑÙÓÙ× ÐÐ º»ÜÑÔÐºÔÔ¸ ÐÒ ½ Ó× Ó ÀÌÙÔÐÓÔÖØÓÖ ´µ º»ÜÑÔÐºÔÔ¸ ÐÒ ½ ÀÌÙÔÐÓÔÖØÓÖ ´ÓÒ×Ø ÀÌÙÔÐ²µ ÓÒ×Ø º»ÜÑÔÐºÔÔ¸ ÐÒ ½ ÀÌÙÔÐÓÔÖØÓÖ ´ÓÙÐµ ÓÒ×Ø º»ÜÑÔÐºÔÔ¸ ÐÒ ½ ÀÌÙÔÐÓÔÖØÓÖ ´ÒØµ ÓÒ×Ø are reported by the compiler. Both errors are caused by conflicting operators. In this case one either has to change the HDevelop or the C++ program. To understand how, let us look at the code which caused the errors above. 1 For the first error the C++ program would look like this: ÀÌÙÔÐ Ì½¸Ì¾ Ì½ ¾ Ì¾ Because there is no operator ÒØ ÀÌÙÔÐ a compiler error is given. This error can be handled in two ways: 1. Do appropriate type casting in C++: Ì½ ÀÌÙÔÐ´¾µ Ì¾ 2. Change the order of the Operands in HDevelop and export the program again: Ì½ Ì¾ ¾ Both changes will do. The first one would be used by the code generation anyway. The second error mentioned above is caused by a similar reason. The program might look like this: ÀÌÙÔÐ Ì½¸Ì¾ ÐÓÒ ÚÐ Ì½ Ì¾ ÚÐ 1 Both concrete errors shown above are hypothetical, as they would be avoided by the automatic code generation in this special case. But they are good examples for similar errors that might be caused by conflicting operators. HALCON 6.0
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HALCON Version 6.0 MVTec Software G
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About This Manual This manual is a
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Contents 1 Introducing HDevelop 1 1
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Contents iii comment . . . . . . .
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Chapter 1 Introducing HDevelop In f
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1.2. EXAMPLE SESSION 3 Figure 1.1:
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1.2. EXAMPLE SESSION 5 Figure 1.2:
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1.3. ADDITIONAL SOURCES OF INFORMAT
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Chapter 2 Graphical User Interface
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2.3. MAIN WINDOW 11 Figure 2.1: The
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2.3. MAIN WINDOW 13 A security chec
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2.3. MAIN WINDOW 15 a directory whe
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2.3. MAIN WINDOW 17 Figure 2.7: The
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2.3. MAIN WINDOW 19 and not HDevelo
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2.3. MAIN WINDOW 21 Figure 2.10: Ma
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2.3. MAIN WINDOW 23 2.3.2.4 The Men
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2.3. MAIN WINDOW 25 Figure 2.13: On
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2.3. MAIN WINDOW 27 in a graphics w
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2.3. MAIN WINDOW 29 Figure 2.16: On
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2.3. MAIN WINDOW 31 Figure 2.17: Co
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Page 47 and 48: 2.3. MAIN WINDOW 39 output paramete
Page 49 and 50: 2.3. MAIN WINDOW 41 is registered i
Page 51 and 52: 2.3. MAIN WINDOW 43 ËÙ×ØÓÒ×
Page 53 and 54: 2.3. MAIN WINDOW 45 ÏÒÓÛ º ×
Page 55 and 56: 2.3. MAIN WINDOW 47 Figure 2.31: Th
Page 57 and 58: 2.5. OPERATOR WINDOW 49 The program
Page 59 and 60: 2.5. OPERATOR WINDOW 51 Please refe
Page 61 and 62: 2.6. VARIABLE WINDOW 53 operator ha
Page 63 and 64: 2.6. VARIABLE WINDOW 55 aspect rati
Page 65 and 66: 2.7. GRAPHICS WINDOW 57 Figure 2.38
Page 67 and 68: Chapter 3 Language The following ch
Page 69 and 70: 3.2. CONTROL TYPES AND CONSTANTS 61
Page 71 and 72: 3.4. OPERATIONS ON ICONIC OBJECTS 6
Page 73 and 74: 3.5. EXPRESSIONS FOR INPUT CONTROL
Page 85 and 86: 3.6. RESERVED WORDS 77 ÓÖ, ÜÓÖ
Page 87 and 88: 3.8. LIMITATIONS 79 In the followin
Page 89 and 90: Chapter 4 Code Generation The idea
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Page 97 and 98: 4.3. CODE GENERATION FOR C 89 4.3 C
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Page 103 and 104: 5.2. CAPILLARY VESSEL 95 ÚÐÓ×Û
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Page 107 and 108: 5.3. PARTICLES 99 each. Now it is e
Page 109 and 110: 5.4. ANNUAL RINGS 101 ÚÐÖÛÒÓ
Page 111 and 112: 5.5. BONDING 103 Figure 5.9: Exampl
Page 113 and 114: 5.7. DEVICES 105 Figure 5.11: Calib
Page 115 and 116: 5.7. DEVICES 107 Figure 5.13: Resis
Page 117 and 118: 5.8. CELL WALLS 109 Figure 5.15: Mi
Page 119 and 120: 5.10. EXCEPTION HANDLING 111 Figure
Page 121 and 122: 5.11. ROAD SCENE 113 any case. All
Page 123 and 124: 5.11. ROAD SCENE 115 tures. Hence a
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Page 127 and 128: 6.5. RESTRICTIONS 119 Figure 6.1: E
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Page 131 and 132: 4 APPENDIX A. CONTROL Attention For
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Page 135 and 136: 8 APPENDIX A. CONTROL ÚÙÔØÛÒ
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Page 139 and 140: 12 APPENDIX B. DEVELOP Attention If
Page 141 and 142: 14 APPENDIX B. DEVELOP Ú ÓÔÒ Û
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16 APPENDIX B. DEVELOP Ú Ò×ÔØ
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18 APPENDIX B. DEVELOP Parallelizat
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20 APPENDIX B. DEVELOP º ÀØ (inp
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22 APPENDIX B. DEVELOP ’black’
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24 APPENDIX B. DEVELOP Parameter º
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26 APPENDIX B. DEVELOP Parameter º
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28 APPENDIX B. DEVELOP If ÊÓÛ½
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30 APPENDIX B. DEVELOP Ú ×Ø ÛÒ
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32 APPENDIX B. DEVELOP Possible Suc
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34 APPENDIX B. DEVELOP See Also Ú
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36 APPENDIX B. DEVELOP HDevelop / 2
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38 APPENDIX C. GLOSSARY Operator wi
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40 Index Ú ×Ø ÔÖØ, 27, 39 Ú
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42 Index Operator Data base, 37 Nam
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44 Index HDevelop / 2000-11-16
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