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Path: sun.soe.clarkson.edu!cline From: cline@sun.soe.clarkson.edu (Marshall Cline) Newsgroups: comp.lang.c++ Subject: C++ FAQ: posting #4/4 Followup-To: comp.lang.c++ Date: 13 Apr 1996 17:41:36 GMT Organization: Paradigm Shift, Inc (technology consulting) Sender: cline@sun.soe.clarkson.edu Distribution: world Expires: +1 month Message-ID: <4kop0g$l61@library.erc.clarkson.edu> Reply-To: cline@parashift.com (Marshall Cline) NNTP-Posting-Host: sun.soe.clarkson.edu Summary: Please read this before posting to comp.lang.c++ Archive-name: C++-faq/part4_4 comp.lang.c++ Frequently Asked Questions list (with answers, fortunately). Copyright (C) 1991-96 Marshall P. Cline, Ph.D. Posting 4 of 4. Posting #1 explains copying permissions, (no)warranty, table-of-contents, etc ============================================================================== SECTION 17: Linkage-to/relationship-with C ============================================================================== Q111: How can I call a C function "f(int,char,float)" from C++ code? Tell the C++ compiler that it is a C function: extern "C" void f(int,char,float); Be sure to include the full function prototype. A block of many C functions can be grouped via braces, as in: extern "C" { void* malloc(size_t); char* strcpy(char* dest, const char* src); int printf(const char* fmt, ...); } ============================================================================== Q112: How can I include a C header file in my C++ code? If it's a standard header file, you don't have to do anything unusual. E.g., #include <stdio.h> If it's not one of the system-provided standard header files, you may need to wrap the '#include' line in an 'extern "C" {...}' construct (but please note that this is not necessary for the standard header files such as '<stdio.h>'): extern "C" { #include "my-C-code.h" } Note: If you have the ability to change the .h file, please see the next FAQ. ============================================================================== Q113: How can I modify a C header file so it can be #included in C++ code? If the C header file is a standard header (e.g., 'stdio.h'), you don't have to do anything; see two FAQs back. If you can't change the header file (e.g., if you don't have write access to the file), see the previous FAQ. If you are able to change the C header file, you should strongly consider adding the 'extern "C" {...}' logic inside the header file to make it easier for C++ users to #include it into their C++ code. Naturally you must wrap the 'extern "C" {' and '}' lines in an '#ifdef' so they won't be seen by normal C compilers. Step #1: put the following lines at the very top of your C header file: #ifdef __cplusplus extern "C" { #endif Step #2: put the following lines at the very bottom of your C header file: #ifdef __cplusplus } #endif ============================================================================== Q114: How can I create a C++ function "f(int,char,float)" that is callable by my C code? The C++ compiler must know that "f(int,char,float)" is to be called by a C compiler using the same "extern C" construct detailed in the previous FAQ. Then you define the function in your C++ module: extern "C" void f(int,char,float); //... void f(int x, char y, float z) { //... } The "extern C" line tells the compiler that the external information sent to the linker should use C calling conventions and name mangling (e.g., preceded by a single underscore). Since name overloading isn't supported by C, you can't make several overloaded fns simultaneously callable by a C program. Caveats and implementation dependencies: * your "main()" should be compiled with your C++ compiler (for static init). * your C++ compiler should direct the linking process (for special libraries). * your C and C++ compilers may need to come from same vendor and have compatible versions (i.e., needs same calling convention, etc.). ============================================================================== Q115: Why's the linker giving errors for C/C++ fns being called from C++/C fns? See the previous two FAQs on how to use "extern "C"." ============================================================================== Q116: How can I pass an object of a C++ class to/from a C function? Here's an example: /****** C/C++ header file: Fred.h ******/ #ifdef __cplusplus /*"__cplusplus" is #defined if/only-if compiler is C++*/ extern "C" { #endif #ifdef __STDC__ extern void c_fn(struct Fred*); /* ANSI-C prototypes */ extern struct Fred* cplusplus_callback_fn(struct Fred*); #else extern void c_fn(); /* K&R style */ extern struct Fred* cplusplus_callback_fn(); #endif #ifdef __cplusplus } #endif #ifdef __cplusplus class Fred { public: Fred(); void wilma(int); private: int a_; }; #endif "Fred.C" would be a C++ module: #include "Fred.h" Fred::Fred() : a_(0) { } void Fred::wilma(int a) { } Fred* cplusplus_callback_fn(Fred* fred) { fred->wilma(123); return fred; } "main.C" would be a C++ module: #include "Fred.h" int main() { Fred fred; c_fn(&fred); return 0; } "c-fn.c" would be a C module: #include "Fred.h" void c_fn(struct Fred* fred) { cplusplus_callback_fn(fred); } Passing ptrs to C++ objects to/from C fns will FAIL if you pass and get back something that isn't EXACTLY the same pointer. For example, DON'T pass a base class ptr and receive back a derived class ptr, since your C compiler won't understand the pointer conversions necessary to handle multiple and/or virtual inheritance. ============================================================================== Q117: Can my C function access data in an object of a C++ class? Sometimes. (First read the previous FAQ on passing C++ objects to/from C functions.) You can safely access a C++ object's data from a C function if the C++ class: * has no virtual functions (including inherited virtual fns) * has all its data in the same access-level section (private/protected/public) * has no fully-contained subobjects with virtual fns If the C++ class has any base classes at all (or if any fully contained subobjects have base classes), accessing the data will TECHNICALLY be non-portable, since class layout under inheritance isn't imposed by the language. However in practice, all C++ compilers do it the same way: the base class object appears first (in left-to-right order in the event of multiple inheritance), and subobjects follow. Furthermore, if the class (or any base class) contains any virtual functions, you can often (but less than always) assume a "void*" appears in the object either at the location of the first virtual function or as the first word in the object. Again, this is not required by the language, but it is the way "everyone" does it. If the class has any virtual base classes, it is even more complicated and less portable. One common implementation technique is for objects to contain an object of the virtual base class (V) last (regardless of where "V" shows up as a virtual base class in the inheritance hierarchy). The rest of the object's parts appear in the normal order. Every derived class that has V as a virtual base class actually has a POINTER to the V part of the final object. ============================================================================== Q118: Why do I feel like I'm "further from the machine" in C++ as opposed to C? Because you are. As an OOPL, C++ allows you to model the problem domain itself, which allows you to program in the language of the problem domain rather than in the language of the solution domain. One of C's great strengths is the fact that it has "no hidden mechanism": what you see is what you get. You can read a C program and "see" every clock cycle. This is not the case in C++; old line C programmers (such as many of us once were) are often ambivalent (can anyone say, "hostile") about this feature, but they soon realize that it provides a level of abstraction and economy of expression which lowers maintenance costs without destroying run-time performance. Naturally you can write bad code in any language; C++ doesn't guarantee any particular level of quality, reusability, abstraction, or any other measure of "goodness." C++ doesn't try to make it impossible for bad programmers to write bad programs; it enables reasonable developers to create superior software. ============================================================================== SECTION 18: Pointers to member functions ============================================================================== Q119: Is the type of "ptr-to-member-fn" different from "ptr-to-fn"? Yep. Consider the following function: int f(char a, float b); If this is an ordinary function, its type is: int (*) (char,float); If this is a method of class Fred, its type is: int (Fred::*)(char,float); ============================================================================== Q120: How do I pass a ptr to member fn to a signal handler, X event callback, etc? Don't. Because a member function is meaningless without an object to invoke it on, you can't do this directly (if The X Windows System was rewritten in C++, it would probably pass references to OBJECTS around, not just pointers to fns; naturally the objects would embody the required function and probably a whole lot more). As a patch for existing software, use a top-level (non-member) function as a wrapper which takes an object obtained through some other technique (held in a global, perhaps). The top-level function would apply the desired member function against the global object. E.g., suppose you want to call Fred::memfn() on interrupt: class Fred { public: void memfn(); static void staticmemfn(); //a static member fn can handle it //... }; //wrapper fn remembers the object on which to invoke memfn in a global: Fred* object_which_will_handle_signal; void Fred_memfn_wrapper() { object_which_will_handle_signal->memfn(); } main() { /* signal(SIGINT, Fred::memfn); */ //Can NOT do this signal(SIGINT, Fred_memfn_wrapper); //Ok signal(SIGINT, Fred::staticmemfn); //Also Ok } Note: static member functions do not require an actual object to be invoked, so ptrs-to-static-member-fns are type compatible with regular ptrs-to-fns (see ARM ["Annotated Reference Manual"] p.25, 158). ============================================================================== Q121: Why do I keep getting compile errors (type mismatch) when I try to use a member function as an interrupt service routine? This is a special case of the previous two questions, therefore read the previous two answers first. Non-static member functions have a hidden parameter that corresponds to the 'this' pointer. The 'this' pointer points to the instance data for the object. The interrupt hardware/firmware in the system is not capable of providing the 'this' pointer argument. You must use "normal" functions (non class members) or static member functions as interrupt service routines. One possible solution is to use a static member as the interrupt service routine and have that function look somewhere to find the instance/member pair that should be called on interrupt. Thus the effect is that a normal method is invoked on an interrupt, but for technical reasons you need to call an intermediate function first. ============================================================================== Q122: Why am I having trouble taking the address of a C++ function? This is a corollary to the previous FAQ. Long answer: In C++, member fns have an implicit parameter which points to the object (the "this" ptr inside the member fn). Normal C fns can be thought of as having a different calling convention from member fns, so the types of their ptrs (ptr-to-member-fn vs ptr-to-fn) are different and incompatible. C++ introduces a new type of ptr, called a ptr-to-member, which can be invoked only by providing an object (see ARM ["Annotated Reference Manual"] 5.5). NOTE: do NOT attempt to "cast" a ptr-to-mem-fn into a ptr-to-fn; the result is undefined and probably disastrous. E.g., a ptr-to- member-fn is NOT required to contain the machine addr of the appropriate fn (see ARM, 8.1.2c, p.158). As was said in the last example, if you have a ptr to a regular C fn, use either a top-level (non-member) fn, or a "static" (class) member fn. ============================================================================== Q123: How do I declare an array of pointers to member functions? Keep your sanity with "typedef". class Fred { public: int f(char x, float y); int g(char x, float y); int h(char x, float y); int i(char x, float y); //... }; typedef int (Fred::*FredPtr)(char x, float y); Here's the array of pointers to member functions: FredPtr a[4] = { &Fred::f, &Fred::g, &Fred::h, &Fred::i }; To call one of the member functions on object "fred": void userCode(Fred& fred, int methodNum, char x, float y) { //assume "methodNum" is between 0 and 3 inclusive (fred.*a[methodNum])(x, y); } You can make the call somewhat clearer using a #define: #define callMethod(object,ptrToMethod) ((object).*(ptrToMethod)) callMethod(fred, a[methodNum]) (x, y); ============================================================================== SECTION 19: Container classes and templates ============================================================================== Q124: How can I build a <favorite container> of objects of different types? You can't, but you can fake it pretty well. In C/C++ all arrays are homogeneous (i.e., the elements are all the same type). However, with an extra layer of indirection you can give the appearance of a heterogeneous container (a heterogeneous container is a container where the contained objects are of different types). There are two cases with heterogeneous containers. The first case occurs when all objects you want to store in a container are publically derived from a common base class. You can then declare/define your container to hold pointers to the base class. You indirectly store a derived class object in a container by storing the object's address as an element in the container. You can then access objects in the container indirectly through the pointers (enjoying polymorphic behavior). If you need to know the exact type of the object in the container you can use 'dynamic_cast<>' or 'typeid()'. You'll probably need the virtual constructor (a.k.a. cloning) idiom to copy a container of disparate object types. The downside of this approach is that it makes memory management a little more problematic (who "owns" the pointed-to objects? if you 'delete' these pointed-to objects when you destroy the container, how can you guarantee that no one else has a copy of one of these pointers? if you don't 'delete' these pointed-to objects when you destroy the container, how can you be sure that someone else will eventually do the 'delete'ing?). It also makes copying the container more complex (may actually break the container's copying functions since you don't want to copy the pointers, at least not when the container "owns" the pointed-to objects). The second case occurs when the object types are disjoint -- they do not share a common base class. The approach here is to use a handle class. The container is a container of handle objects (by value or by pointer, your choice; by value is easier). Each handle object knows how to "hold on to" (i.e. ,maintain a pointer to) one of the objects you want to put in the container. You can use either a single handle class with several different types of pointers as instance data, or a hierarchy of handle classes that shadow the various types you wish to contain (requires the container be of handle base clsss pointers). The downside of this approach is that it opens up the handle class(es) to maintenance every time you change the set of types that can be contained. The benefit is that you can use the handle class(es) to encapsulate most of the ugliness of memory management and object lifetime. Thus using handle objects may be beneficial even in the first case. [Adapted with permission from an email from Phil Staite, pstaite@vnet.ibm.com]. ============================================================================== Q125: How can I insert/access/change elements from a linked list/hashtable/etc? I'll use an "inserting into a linked list" as a prototypical example. It's easy to allow insertion at the head and tail of the list, but limiting ourselves to these would produce a library that is too weak (a weak library is almost worse than no library). This answer will be a lot to swallow for novice C++'ers, so I'll give a couple of options. The first option is easiest; the second and third are better. [1] Empower the "List" with a "current location," and methods such as advance(), backup(), atEnd(), atBegin(), getCurrElem(), setCurrElem(Elem), insertElem(Elem), and removeElem(). Although this works in small examples, the notion of "a" current position makes it difficult to access elements at two or more positions within the List (e.g., "for all pairs x,y do the following..."). [2] Remove the above methods from the List itself, and move them to a separate class, "ListPosition." ListPosition would act as a "current position" within a List. This allows multiple positions within the same List. ListPosition would be a friend of List, so List can hide its innards from the outside world (else the innards of List would have to be publicized via public methods in List). Note: ListPosition can use operator overloading for things like advance() and backup(), since operator overloading is syntactic sugar for normal methods. [3] Consider the entire iteration as an atomic event, and create a class template to embodies this event. This enhances performance by allowing the public access methods (which may be virtual fns) to be avoided during the inner loop. Unfortunately you get extra object code in the application, since templates gain speed by duplicating code. For more, see [Koenig, "Templates as interfaces," JOOP, 4, 5 (Sept 91)], and [Stroustrup, "The C++ Programming Language Second Edition," under "Comparator"]. ============================================================================== Q126: What's the idea behind "templates"? A template is a cookie-cutter that specifies how to cut cookies that all look pretty much the same (although the cookies can be made of various kinds of dough, they'll all have the same basic shape). In the same way, a class template is a cookie cutter to description of how to build a family of classes that all look basically the same, and a function template describes how to build a family of similar looking functions. Class templates are often used to build type safe containers (although this only scratches the surface for how they can be used). ============================================================================== Q127: What's the syntax / semantics for a "function template"? Consider this function that swaps its two integer arguments: void swap(int& x, int& y) { int tmp = x; x = y; y = tmp; } If we also had to swap floats, longs, Strings, Sets, and FileSystems, we'd get pretty tired of coding lines that look almost identical except for the type. Mindless repetition is an ideal job for a computer, hence a function template: template<class T> void swap(T& x, T& y) { T tmp = x; x = y; y = tmp; } Every time we used "swap()" with a given pair of types, the compiler will go to the above definition and will create yet another "template function" as an instantiation of the above. E.g., main() { int i,j; /*...*/ swap(i,j); //instantiates a swap for "int" float a,b; /*...*/ swap(a,b); //instantiates a swap for "float" char c,d; /*...*/ swap(c,d); //instantiates a swap for "char" String s,t; /*...*/ swap(s,t); //instantiates a swap for "String" } (note: a "template function" is the instantiation of a "function template"). ============================================================================== Q128: What's the syntax / semantics for a "class template"? Consider a container class of that acts like an array of integers: //this would go into a header file such as "Array.h" class Array { public: Array(int len=10) : len_(len), data_(new int[len]){} ~Array() { delete [] data_; } int len() const { return len_; } const int& operator[](int i) const { data_[check(i)]; } int& operator[](int i) { data_[check(i)]; } Array(const Array&); Array& operator= (const Array&); private: int len_; int* data_; int check(int i) const { if (i < 0 || i >= len_) throw BoundsViol("Array", i, len_); return i; } }; Just as with "swap()" above, repeating the above over and over for Array of float, of char, of String, of Array-of-String, etc, will become tedious. //this would go into a header file such as "Array.h" template<class T> class Array { public: Array(int len=10) : len_(len), data_(new T[len]) { } ~Array() { delete [] data_; } int len() const { return len_; } const T& operator[](int i) const { data_[check(i)]; } T& operator[](int i) { data_[check(i)]; } Array(const Array<T>&); Array& operator= (const Array<T>&); private: int len_; T* data_; int check(int i) const { if (i < 0 || i >= len_) throw BoundsViol("Array", i, len_); return i; } }; Unlike template functions, template classes (instantiations of class templates) need to be explicit about the parameters over which they are instantiating: main() { Array<int> ai; Array<float> af; Array<char*> ac; Array<String> as; Array< Array<int> > aai; } // ^^^-- note the space; do NOT use "Array<Array<int>>" // (the compiler sees ">>" as a single token). ============================================================================== Q129: What is a "parameterized type"? Another way to say, "class templates." A parameterized type is a type that is parameterized over another type or some value. List<int> is a type ("List") parameterized over another type ("int"). ============================================================================== Q130: What is "genericity"? Yet another way to say, "class templates." Not to be confused with "generality" (which just means avoiding solutions which are overly specific), "genericity" means class templates. ============================================================================== SECTION 20: Libraries ============================================================================== Q131: Where can I get a copy of "STL"? "STL" is the "Standard Templates Library". You can get a copy from: An STL site: ftp://ftp.cs.rpi.edu/pub/stl STL HP official site: ftp://butler.hpl.hp.com/stl/ Mirror site in Europe: http://www.maths.warwick.ac.uk/ftp/mirrors/c++/stl/ STL code alternate: ftp://ftp.cs.rpi.edu/stl STL code + examples: http://www.cs.rpi.edu/~musser/stl.html STL hacks for GCC-2.6.3 are part of the GNU libg++ package 2.6.2.1 or later (and they may be in an earlier version as well). Thanks to Mike Lindner. ============================================================================== Q132: Where can I get help on how to use STL? Kenny Zalewski's STL guide: http://www.cs.rpi.edu/projects/STL/htdocs/stl-new.html Dave Musser's STL guide: http://www.cs.rpi.edu/~musser/stl.html Mumit's STL Newbie's guide: http://www.xraylith.wisc.edu/~khan/software/stl/STL.newbie.html ============================================================================== Q133: Where can I ftp the code that accompanies "Numerical Recipes"? This software is sold and there for it would be illegal to provide it on the net. However, it's only about $30. ============================================================================== Q134: Why is my executable so large? Many people are surprised by how big executables are, especially if the source code is trivial. For example, a simple "hello world" program can generate an executable that is larger than most people expect (40+K bytes). One reason executables can be large is that portions of the C++ runtime library gets linked with your program. How much gets linked in depends on how much of it you are using, and on how the implementor split up the library into pieces. For example, the iostream library is quite large, and consists of numerous classes and virtual functions. Using any part of it might pull in nearly all of the iostream code as a result of the interdependencies. You might be able to make your program smaller by using a dynamically-linked version of the library instead of the static version. You have to consult your compiler manuals or the vendor's technical support for a more detailed answer. ============================================================================== SECTION 21: Nuances of particular implementations ============================================================================== Q135: 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 (~1 Meg; 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. ============================================================================== Q136: Is there a yacc-able C++ grammar? Jim Roskind is the author of a yacc grammar for C++. It's roughly compatible with the portion of the language implemented by USL cfront 2.0 (no templates, no exceptions, no run-time-type-identification). Jim's grammar deviates from C++ in a couple of minor-but-subtle ways. The grammar can be accessed on-line as follows: * ftp://ics.uci.edu/gnu/c++grammar2.0.tar.Z (ics.uci.edu is IP 128.195.1.1) * ftp://mach1.npac.syr.edu/pub/C++/c++grammar2.0.tar.Z (mach1.npac.syr.edu is IP 128.230.7.14) [NOTE: I was told that these ftp addresses are no longer valid. Would someone please either confirm or deny this assertion, and would someone please let me know of an alternate address. Thanks; Marshall Cline] ============================================================================== Q137: 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 [] ptr_to_array." * 3.0 includes fully-nested classes, templates and "i++" vs "++i." * 4.0 will include exceptions. ============================================================================== Q138: 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: 1) Number and type of hidden arguments to member functions. 1a) is 'this' handled specially? 1b) where is the return-by-value pointer passed? 2) Assuming a vtable is used: 2a) what is its contents and layout? 2b) where/how is the adjustment to 'this' made for multiple inheritance? 3) How are classes laid out, including: 3a) location of base classes? 3b) handling of virtual base classes? 3c) location of vtable pointers, if vtables are used? 4) Calling convention for functions, including: 4a) does caller or callee adjust the stack? 4b) where are the actual parameters placed? 4c) in what order are the actual parameters passed? 4d) how are registers saved? 4e) where does the return value go? 4f) special rules for passing or returning structs or doubles? 4g) special rules for saving registers when calling leaf functions? 5) How is the run-time-type-identification laid out? 6) How does the runtime exception handling system know which local objects need to be destructed during an exception throw? ============================================================================== SECTION 22: Miscellaneous technical and environmental issues ============================================================================== SUBSECTION 22A: Miscellaneous technical issues: ============================================================================== Q139: Why are classes with static data members getting linker errors? Static data members must be explicitly defined in exactly one module. E.g., class Fred { public: //... private: static int i_; //declares static data member "Fred::i_" //... }; The linker will holler at you ("Fred::i_ is not defined") unless you define (as opposed to declare) "Fred::i_" in (exactly) one of your source files: int Fred::i_ = some_expression_evaluating_to_an_int; or: int Fred::i_; The usual place to define static data members of class "Fred" is file "Fred.C" (or "Fred.cpp", etc; whatever filename extension you use). ============================================================================== Q140: What's the difference between the keywords struct and class? The members and base classes of a struct are public by default, while in class, they default to private. Note: you should make your base classes EXPLICITLY public, private, or protected, rather than relying on the defaults. "struct" and "class" are otherwise functionally equivalent. ============================================================================== Q141: Why can't I overload a function by its return type? If you declare both "char f()" and "float f()", the compiler gives you an error message, since calling simply "f()" would be ambiguous. ============================================================================== Q142: What is "persistence"? What is a "persistent object"? A persistent object can live after the program which created it has stopped. Persistent objects can even outlive different versions of the creating program, can outlive the disk system, the operating system, or even the hardware on which the OS was running when they were created. The challenge with persistent objects is to effectively store their method code out on secondary storage along with their data bits (and the data bits and method code of all member objects, and of all their member objects and base classes, etc). This is non-trivial when you have to do it yourself. In C++, you have to do it yourself. C++/OO databases can help hide the mechanism for all this. ============================================================================== Q143: Why is floating point so inaccurate? Why doesn't this print 0.43? #include<iostream.h> main() { float a = 1000.43; float b = 1000.0; cout << a - b << '\n'; } (note, on one C++ implementation, this prints 0.429993) Disclaimer: Frustration with rounding/truncation/approximation isn't really a C++ issue. It's a computer science issue. However, people keep asking about it on comp.lang.c++, so here's a nominal answer. Answer: Floating point is an approximation. The IEEE standard for 32 bit float supports 1 bit of sign, 8 bits of exponent, and 23 bits of mantissa. Since a normalized binary-point mantissa always has the form 1.xxxxx... the leading 1 is dropped and you get effectively 24 bits of mantissa. The number 1000.43 (and many, many others) is not exactly representable in float or double format. 1000.43 is actually represented as the following bitpattern (the 's' shows the position of the sign bit, the 'e's show the positions of the exponent bits, and the 'm's show the positions of the mantissa bits): seeeeeeeemmmmmmmmmmmmmmmmmmmmmmm 01000100011110100001101110000101 The shifted mantissa is 1111101000.01101110000101 or 1000 + 7045/16384. The fractional part is 0.429992675781. With 24 bits of mantissa you only get about 1 part in 16M of precision for float. The 'double' type provides more precision (53 bits of mantissa). ============================================================================== SUBSECTION 22B: Miscellaneous environmental issues: ============================================================================== Q144: Is there a TeX or LaTeX macro that fixes the spacing on "C++"? Yes, here are three (the first prevents line breaks between the "C" and "++"): \def\CC{{C\nolinebreak[4]\hspace{-.05em}\raisebox{.4ex}{\tiny\bf ++}}} \def\CC{C\raise.22ex\hbox{{\footnotesize +}}\raise.22ex\hbox{\footnotesize +}} \def\CC{{C\hspace{-.05em}\raisebox{.4ex}{\tiny\bf ++}}} ============================================================================== Q145: Where can I access C++2LaTeX, a LaTeX pretty printer for C++ source? ftp://ftp.german.eu.net/pub/packages/TeX/support/pretty/C++2LaTeX-3.02.tar.gz ============================================================================== Q146: Where can I access "tgrind," a pretty printer for C++/C/etc source? "tgrind" reads a C++ source file, and spits out something that looks pretty on most Unix printers. It usually comes with the public distribution of TeX and LaTeX; look in the directory: "...tex82/contrib/van/tgrind". A more up-to-date version of tgrind by Jerry Leichter can be found on: venus.ycc.yale.edu in [.TGRIND]. ============================================================================== Q147: Is there a C++-mode for GNU emacs? If so, where can I get it? Yes, there is a C++-mode for GNU emacs. The latest and greatest version of C++-mode (and c-mode) is implemented in the file cc-mode.el. It is an extension of Detlef & Clamen's version. A version is included with emacs. Newer version are availiable from the elisp archives. ============================================================================== Q148: Where can I get OS-specific FAQs answered (e.g.,BC++,DOS,Windows,etc)? See one of the following: * comp.os.msdos.programmer * comp.windows.ms.programmer * comp.unix.programmer [If anyone has an email address for a BC++, VC++, or Semantic C++ bug list and/or discussion mailing list, please let me know how to subscribe, and I'll mention it here]. ============================================================================== Q149: Why does my DOS C++ program says "Sorry: floating point code not linked"? The compiler attempts to save space in the executable by not including the float-to-string format conversion routines unless they are necessary, but sometimes it guesses wrong, and gives you the above error message. You can fix this by (1) using <iostream.h> instead of <stdio.h>, or (2) by including the following function somewhere in your compilation (but don't call it!): static void dummyfloat(float *x) { float y; dummyfloat(&y); } See FAQ on stream I/O for more reasons to use <iostream.h> vs <stdio.h>. ============================================================================== Q150: Why does my BC++ Windows app crash when I'm not running the BC45 IDE? If you're using BC++ for a Windows app, and it works ok as long as you have the BC45 IDE running, but when the BC45 IDE is shut down you get an exception during the creation of a window, then add the following line of code to the InitMainWindow() method of your application ("YourApp::InitMainWindow()"): EnableBWCC(TRUE); ============================================================================== -- Paradigm Shift, Inc. / P.O. Box 5108 / Potsdam, NY 13676 Technology consulting services cline@parashift.com / Voice: 315-353-6100 / FAX: 315-353-6110