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| 2 | ========================================================= |
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| 3 | Geant4 - an Object-Oriented Toolkit for Simulation in HEP |
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| 4 | ========================================================= |
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| 5 | |
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| 6 | ExampleP02 |
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| 7 | ---------- |
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| 8 | |
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| 9 | General description |
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| 10 | ------------------- |
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| 11 | |
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| 12 | This example shows how to store in a binary file and how to |
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| 13 | read back the geometry tree using the 'reflection' technique for |
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| 14 | persistency provided by the Reflex tool also included in ROOT. The |
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| 15 | Reflex tool allows to create a dictionary for the geometry classes, |
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| 16 | making then possible to save the entire tree in a .root file. |
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| 17 | |
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| 18 | The provided makefile produces the executable: 'exampleP02'. In order |
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| 19 | to run it one has to specify the argument, either 'write' or |
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| 20 | 'read'. In the first case the geometry is instaciated in the standard |
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| 21 | way and then saved into the root file (geo.root). In the second case, |
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| 22 | the geometry is read from geo.root file. |
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| 23 | |
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| 24 | |
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| 25 | Building and running the example |
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| 26 | -------------------------------- |
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| 27 | |
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| 28 | Before buidling and/or running the example you need to set the |
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| 29 | following environment variables: |
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| 30 | |
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| 31 | ROOTSYS - ROOT installation directory, it is required to run ROOT |
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| 32 | |
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| 33 | GCCXMLPATH - gccxml binary directory, it is needed by ROOT for the |
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| 34 | dictionary generation |
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| 35 | LD_LIBRARY_PATH - to include the ROOT library path and the path to |
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| 36 | the dictionary library, i.e., for tcsh UNIX shell: |
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| 37 | setenv LD_LIBRARY_PATH ${LD_LIBRARY_PATH}:$ROOTSYS/lib: |
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| 38 | $G4WORKDIR/tmp/$G4SYSTEM/exampleP01 |
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| 39 | |
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| 40 | The present version of the example requires that Geant4 headers are |
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| 41 | installed in a single directory referenced by G4INCLUDE, as the standard |
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| 42 | Geant4 installation procedure allows to do. |
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| 43 | |
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| 44 | Once those variables are set (together with the standard Geant4 setup) |
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| 45 | the example can be build by issueing the 'make' command. The final |
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| 46 | executable file can be found in the usual directory: |
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| 47 | |
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| 48 | $G4WORKDIR/bin/$G4SYSTEM/ |
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| 49 | |
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| 50 | |
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| 51 | Remark on dictionary generation |
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| 52 | ------------------------------- |
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| 53 | |
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| 54 | The dictionary is generated by ${ROOTSYS}/bin/genreflex |
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| 55 | tool. The header file including headers for all the classes we want to |
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| 56 | generate the dictionary for should be given as argument. Additionally, |
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| 57 | a so called selection file (xml) should be provided (with -s flag) to |
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| 58 | the genreflex tool (see the GNUmakefile). The role of this file is to |
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| 59 | specify which classes we want to generate the dictionary for. The |
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| 60 | selection file for our dictionary is in xml/ directory. Please refer |
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| 61 | to genreflex manual for more details concerning the usage of that |
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| 62 | tool. |
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| 63 | |
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| 64 | Concerning generating dictionary for the Geant4 objects, there are |
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| 65 | also two technical remarks that need to be made here. The gccxml tool |
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| 66 | (version 0.6.0_patch1) requires all the templated classes to be |
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| 67 | explicitely used somewhere in the included header files in order for |
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| 68 | the generation of the dictionary to be possible. For those templated |
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| 69 | classes for which it is not the case, the problem can be very easily |
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| 70 | solved by instaciating them in the headerfile which is given to |
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| 71 | genreflex (see includes/Classes.h) as argument. |
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| 72 | The second remark is that there is an unfortunate clash of names as |
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| 73 | far as G4String class is concerned. The header of G4String class |
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| 74 | defines __G4String which happens to be the name of a variable used |
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| 75 | within the generated dictionary code. The solution for that is to do |
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| 76 | #undef __G4String in include/Classes.h file. |
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| 77 | |
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| 78 | |
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