How to Understand a Class Structure ?
The class structure and Object-Orientation make possible more modular programming. However, programs consisting of several hundred classes and several hundred thousand lines of code may be difficult to understand, in particular for novice users. ROOT provides a set of tools to help understanding an existing class structure, a data structure in memory or files.
- TClass::Draw can be used to draw the inheritance tree for a given object. All ROOT classes are documented with their associated inheritance tree (see for example TPaveText). This tree can be generated interactively via the command: object->DrawClass() or by selecting the DrawClass item when pointing with the right moose button to an object in a canvas. The tree is automatically generated when a given class is processed through the documentation tool (class THtml). For example:
- TObject::Inspect can be used to view the contents of a given object. A table is shown where, for each data member, its name, current value and its title are given.
- TObject::Dump is the same as TObject::Inspect, except that the output is on stdout. An object dump can be written to a file. Example: Produces the following dump of the object f:
TFile f("hsimple.root"); // connects a file f.Dump(); // dump the object f
fBEGIN 64 First used byte in file fEND 459500 Last used byte in file fVersion 9010 File format version fCompress 1 (=1 file is compressed, 0 otherwise) fOption.*fData READ fUnits 4 Number of bytes for file pointers fSeekFree 459414 Location on disk of free segments structure fNbytesFree 86 Number of bytes for free segments structure fWritten 0 Number of objects written so far fSumBuffer 0 Sum of buffer sizes of objects written so far fSum2Buffer 0 Sum of squares of buffer sizes of objects written so far *fStream ->4033f690 Input file stream identifier *fOStream ->0 Output stream (output on same file as fStream) *fFree ->0 Free segments linked list table fModified 1 true if directory has been modified fWritable 0 true if directory is writable fDatimeC.fDatime 139248235 Date (relative to 1995) + time fDatimeM.fDatime 139248246 Date (relative to 1995) + time fNbytesKeys 307 Number of bytes for the keys fNbytesName 120 Number of bytes in TNamed at creation time fSeekDir 64 Location of directory on file fSeekParent 0 Location of parent directory on file fSeekKeys 459107 Location of Keys record on file *fFile ->4033f508 pointer to current file in memory *fKeys ->4033f628 Pointer to keys list in memory *fMother ->0 pointer to mother of the list *fIndex ->0 Index of the list *fListHead ->4033f5f0 Pointer to Objects in this directory fName.*fData hsimple.root fTitle.*fData fUniqueID 0 object unique identifier fBits 50331649 bit field status word
- The ROOT general object browser (see TBrowser) can be used to browse collections such as the list of classes, geometries, files and TTrees. A browser can be started from the Start Browser item in the canvas View menu or by creating a browser object. Example: TBrowser b. More than one browser can be active at any time.
- TFile::ls can be used to list objects in a file or directory.
- list->ls() lists objects in a collection pointed by list.
- list->Dump() dumps all objects in a collection pointed by list.
- TFile::Map dumps the structure of a file. One line is printed for every record written to the file with the following information: For example, to see the map of the file generated by the tutorial hsimple, you can type the following commands:
- Date/Time when the object was written. - Position of the object (starting byte number). - Number of bytes occupied by the object. - Object class name. - Compression factor (if file is compressed).
TFile f("hsimple.root"); // connect file f.Map();This produces the following output:970106/120943 At:64 N=150 TFile 970106/120944 At:214 N=28909 TBasket CX = 1.11 970106/120945 At:29123 N=29046 TBasket CX = 1.10 970106/120946 At:58169 N=29021 TBasket CX = 1.10 970106/120946 At:87190 N=28994 TBasket CX = 1.10 970106/120947 At:116184 N=29069 TBasket CX = 1.10 970106/120948 At:145253 N=29101 TBasket CX = 1.10 970106/120948 At:174354 N=29019 TBasket CX = 1.10 970106/120949 At:203373 N=28930 TBasket CX = 1.11 970106/120949 At:232303 N=29040 TBasket CX = 1.10 970106/120950 At:261343 N=29001 TBasket CX = 1.10 970106/120951 At:290344 N=29035 TBasket CX = 1.10 970106/120951 At:319379 N=29003 TBasket CX = 1.10 970106/120952 At:348382 N=29008 TBasket CX = 1.10 970106/120953 At:377390 N=29049 TBasket CX = 1.10 970106/120953 At:406439 N=29025 TBasket CX = 1.10 970106/120953 At:435464 N=455 TH1F CX = 1.80 970106/120954 At:435919 N=1724 TH2F CX = 4.33 970106/120954 At:437643 N=1850 TProfile CX = 1.55 970106/120954 At:439493 N=19614 TNtuple CX = 1.74 970106/120954 At:459107 N=307 TFile 970106/121159 At:459414 N=86 TFile
- gObjectTable->Print(). ROOT keeps tracks of all objects created into a special table in memory. In the development phase of a program, it is frequent to create objects and forget to delete them (memory leaks). Printing the object table shows the number of instances for each class currently active in memory. It also shows the total number of bytes occupied by these objects. Example: gObjectTable->Print(); produces the following output:
Object statistics class cnt on heap size total size heap size ============================================================================ TH1F 1 1 448 448 448 TObject 11 11 12 132 132 TFileType 6 6 36 216 216 TRint 1 1 116 116 116 TClassTable 1 1 12 12 12 TObjectTable 1 1 12 12 12 THashList 5 5 40 200 200 THashTable 5 5 36 180 180 TList 24 24 36 864 864 TStyle 1 1 328 328 328 TGeometry 1 1 64 64 64 TGaxis 1 0 124 124 0 TAxis 6 3 88 528 264 TUnixSystem 1 1 256 256 256 TPostScript 1 1 764 764 764 TOrdCollection 4 4 40 160 160 TEnv 1 1 24 24 24 TBenchmark 1 1 52 52 52 TSignalHandler 1 1 20 20 20 TFileHandler 2 2 20 40 40 TCint 1 1 208 208 208 TFile 1 1 160 160 160 TROOT 1 0 244 244 0 TClass 6 6 64 384 384 TKey 4 4 80 320 320 TStopwatch 1 0 56 56 0 TGuiFactory 2 2 28 56 56 TGXW 1 1 84 84 84 TRandom 1 1 32 32 32 TGX11 1 1 176 176 176 ---------------------------------------------------------------------------- Total: 94 88 3660 6260 5572 ============================================================================
THtml html; html.MakeClass(myclass);
If a data member is a pointer to another object, one can click on the pointer and, in turn, inspect the pointed object,etc.
