[33.1] Where can I get more information on using MFC and Visual C++? [33.2] How do I display text in the status bar using MFC? [33.3] How can I decompile an executable program back into C++ source code? [33.4] Where can I get information about the C++ compiler from {Borland, IBM, Microsoft, Semantic, Sun, etc.}? [33.5] How do compilers use "over-allocation" to remember the number of elements in an allocated array? [33.6] How do compilers use an "associative array" to remember the number of elements in an allocated array? [33.7] If name mangling was standardized, could I link code compiled with compilers from different compiler vendors? [33.8] GNU C++ (g++) produces big executables for tiny programs; Why? [33.9] Is there a yacc-able C++ grammar? [33.10] What is C++ 1.2? 2.0? 2.1? 3.0?
[33.1] Where can I get more information on using MFC and Visual C++? [Recently created (on 5/98). Click here to go to the next FAQ in the "chain" of recent changes.] The MFC/Visual C++ FAQ (http://www.stingray.com/mfc_faq) is maintained by Scot Wingo. [ Top | Bottom | Previous section | Next section ]
[33.2] How do I display text in the status bar using MFC? Use the following code snipped:
CString s = "Text"; CStatusBar* p = (CStatusBar*)AfxGetApp()->m_pMainWnd->GetDescendantWindow(AFX_IDW_STATUS_BAR); p->SetPaneText(1, s);
This works with MFC v.1.00 which hopefully means it will work with other versions as well. [ Top | Bottom | Previous section | Next section ]
[33.3] How can I decompile an executable program back into C++ source code? You gotta be kidding, right? Here are a few of the many reasons this is not even remotely feasible:
What makes you think the program was written in C++ to begin with? Even if you are sure it was originally written (at least partially) in C++, which one of the gazillion C++ compilers produced it? Even if you know the compiler, which particular version of the compiler was used? Even if you know the compiler's manufacturer and version number, what compile-time options were used? Even if you know the compiler's manufacturer and version number and compile-time options, what third party libraries were linked-in, and what was their version? Even if you know all that stuff, most executables have had their debugging information stripped out, so the resulting decompiled code will be totally unreadable. Even if you know everything about the compiler, manufacturer, version number, compile-time options, third party libraries, and debugging information, the cost of writing a decompiler that works with even one particular compiler and has even a modest success rate at generating code would be a monumental effort — on the par with writing the compiler itself from scratch.
But the biggest question is not how you can decompile someone's code, but why do you want to do this? If you're trying to reverse-engineer someone elses code, shame on you; go find honest work. If you're trying to recover from losing your own source, the best suggestion I have is to make better backups next time. [ Top | Bottom | Previous section | Next section ]
[33.4] Where can I get information about the C++ compiler from {Borland, IBM, Microsoft, Semantic, Sun, etc.}? [Recently corrected the URL for Borland C++ & HP C++; added GNU C++, Intel Reference C++, KAI C++, and Portland Group C++ (on 5/98). Click here to go to the next FAQ in the "chain" of recent changes.] In alphabetical order by vendor name:
Borland C++ 5.0 FAQs: http://www.turbopower.com/bcpp/ DJ C++ ("DJGPP"): http://www.delorie.com/ GNU C++ ("g++" or "GCC"): http://www.cygnus.com/ HP C++: http://www.hp.com/lang/cpp/ IBM VisualAge C++: http://www.software.ibm.com/ad/cset/ Intel Reference C++: http://developer.intel.com/design/perftool/icl24/ KAI C++: http://www.allys.cie.fr/ALLYS/KCC-english/v3.2/ Metrowerks C++: http://metrowerks.com or http://www.metrowerks.com Microsoft Visual C++: http://www.microsoft.com/visualc/ Portland Group C++: http://www.pgroup.com Silicon Graphics C++: http://www.sgi.com/Products/DevMagic/products/cplusplus.html Sun Visual WorkShopTM for C++: http://www.sun.com/workshop/visual Symantec C++: http://www.symantec.com/scpp/index_product.html Watcom C++: http://www.powersoft.com/products/languages/watccpl.html
[If anyone has other suggestions that should go into this list, please let me know; thanks; (cline@parashift.com)]. [ Top | Bottom | Previous section | Next section ]
[33.5] How do compilers use "over-allocation" to remember the number of elements in an allocated array? Recall that when you delete[] an array, the runtime system magically knows how many destructors to run. This FAQ describes a technique used by some C++ compilers to do this (the other common technique is to use an associative array). If the compiler uses the "over-allocation" technique, the code for p = new Fred[n] looks something like the following. Note that WORDSIZE is an imaginary machine-dependent constant that is at least sizeof(size_t), possibly rounded up for any alignment constraints. On many machines, this constant will have a value of 4 or 8. It is not a real C++ identifier that will be defined for your compiler.
// Original code: Fred* p = new Fred[n]; char* tmp = (char*) operator new[] (WORDSIZE + n * sizeof(Fred)); Fred* p = (Fred*) (tmp + WORDSIZE); *(size_t*)tmp = n; size_t i; try { for (i = 0; i < n; ++i) new(p + i) Fred(); // Placement new } catch (...) { while (i-- != 0) (p + i)->~Fred(); // Explicit call to the destructor operator delete[] ((char*)p - WORDSIZE); throw; }
Then the delete[] p statement becomes:
// Original code: delete[] p; size_t n = * (size_t*) ((char*)p - WORDSIZE); while (n-- != 0) (p + n)->~Fred(); operator delete[] ((char*)p - WORDSIZE);
Note that the address passed to operator delete[] is not the same as p. Compared to the associative array technique, this technique is faster, but more sensitive to the problem of programmers saying delete p rather than delete[] p. For example, if you make a programming error by saying delete p where you should have said delete[] p, the address that is passed to operator delete(void*) is not the address of any valid heap allocation. This will probably corrupt the heap. Bang! You're dead! [ Top | Bottom | Previous section | Next section ]
[33.6] How do compilers use an "associative array" to remember the number of elements in an allocated array? Recall that when you delete[] an array, the runtime system magically knows how many destructors to run. This FAQ describes a technique used by some C++ compilers to do this (the other common technique is to over-allocate). If the compiler uses the associative array technique, the code for p = new Fred[n] looks something like this (where arrayLengthAssociation is the imaginary name of a hidden, global associative array that maps from void* to "size_t"):
// Original code: Fred* p = new Fred[n]; Fred* p = (Fred*) operator new[] (n * sizeof(Fred)); size_t i; try { for (i = 0; i < n; ++i) new(p + i) Fred(); // Placement new } catch (...) { while (i-- != 0) (p + i)->~Fred(); // Explicit call to the destructor operator delete[] (p); throw; } arrayLengthAssociation.insert(p, n);
Then the delete[] p statement becomes:
// Original code: delete[] p; size_t n = arrayLengthAssociation.lookup(p); while (n-- != 0) (p + n)->~Fred(); operator delete[] (p);
Cfront uses this technique (it uses an AVL tree to implement the associative array). Compared to the over-allocation technique, the associative array technique is slower, but less sensitive to the problem of programmers saying delete p rather than delete[] p. For example, if you make a programming error by saying delete p where you should have said delete[] p, only the first Fred in the array gets destructed, but the heap may survive (unless you've replaced operator delete[] with something that doesn't simply call operator delete, or unless the destructors for the other Fred objects were necessary). [ Top | Bottom | Previous section | Next section ]
[33.7] If name mangling was standardized, could I link code compiled with compilers from different compiler vendors? Short answer: Probably not. In other words, some people would like to see name mangling standards incorporated into the proposed C++ ANSI standards in an attempt to avoiding having to purchase different versions of class libraries for different compiler vendors. However name mangling differences are one of the smallest differences between implementations, even on the same platform. Here is a partial list of other differences:
Number and type of hidden arguments to member functions.
is this handled specially? where is the return-by-value pointer passed?
Assuming a v-table is used:
what is its contents and layout? where/how is the adjustment to this made for multiple and/or virtual inheritance?
How are classes laid out, including:
location of base classes? handling of virtual base classes? location of v-pointers, if they are used at all?
Calling convention for functions, including:
where are the actual parameters placed? in what order are the actual parameters passed? how are registers saved? where does the return value go? does caller or callee pop the stack after the call? special rules for passing or returning structs or doubles? special rules for saving registers when calling leaf functions?
How is the run-time-type-identification laid out? How does the runtime exception handling system know which local objects need to be destructed during an exception throw?
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[33.8] GNU C++ (g++) produces big executables for tiny programs; Why? libg++ (the library used by g++) was probably compiled with debug info (-g). On some machines, recompiling libg++ without debugging can save lots of disk space (approximately 1 MB; the down-side: you'll be unable to trace into libg++ calls). Merely strip-ping the executable doesn't reclaim as much as recompiling without -g followed by subsequent strip-ping the resultant a.out's. Use size a.out to see how big the program code and data segments really are, rather than ls -s a.out which includes the symbol table. [ Top | Bottom | Previous section | Next section ]
[33.9] Is there a yacc-able C++ grammar? There used to be a yacc grammar that was pretty close to C++. As far as I am aware, it has not kept up with the evolving C++ standard. For example, the grammar doesn't handle templates, "exceptions", nor run-time-type-identification, and it deviates from the rest of the language in some subtle ways. It is available at http://srawgw.sra.co.jp/.a/pub/cmd/c++grammar2.0.tar.gz [ Top | Bottom | Previous section | Next section ]
[33.10] What is C++ 1.2? 2.0? 2.1? 3.0? These are not versions of the language, but rather versions of cfront, which was the original C++ translator implemented by AT&T. It has become generally accepted to use these version numbers as if they were versions of the language itself. Very roughly speaking, these are the major features:
2.0 includes multiple/virtual inheritance and pure virtual functions 2.1 includes semi-nested classes and delete[] pointerToArray 3.0 includes fully-nested classes, templates and i++ vs. ++i 4.0 will include exceptions
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