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  • Can we have an anonymous struct as template argument?

    - by nonoitall
    The title is pretty self-explanatory, but here's a simplified example: #include <cstdio> template <typename T> struct MyTemplate { T member; void printMemberSize() { printf("%i\n", sizeof(T)); } }; int main() { MyTemplate<struct { int a; int b; }> t; // <-- compiler doesn't like this t.printMemberSize(); return 0; } The compiler complains when I try to use an anonymous struct as a template argument. What's the best way to achieve something like this without having to have a separate, named struct definition?

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  • How do I use Declarations (type, inline, optimize) in Scheme?

    - by kunjaan
    How do I declare the types of the parameters in order to circumvent type checking? How do I optimize the speed to tell the compiler to run the function as fast as possible like (optimize speed (safety 0))? How do I make an inline function in Scheme? How do I use an unboxed representation of a data object? And finally are any of these important or necessary? Can I depend on my compiler to make these optimizations? thanks, kunjaan.

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  • Safe to cast pointer to a forward-declared class to its true base class in C++?

    - by Matt DiMeo
    In one header file I have: #include "BaseClass.h" // a forward declaration of DerivedClass, which extends class BaseClass. class DerivedClass ; class Foo { DerivedClass *derived ; void someMethod() { // this is the cast I'm worried about. ((BaseClass*)derived)->baseClassMethod() ; } }; Now, DerivedClass is (in its own header file) derived from BaseClass, but the compiler doesn't know that at the time it's reading the definition above for class Foo. However, Foo refers to DerivedClass pointers and DerivedClass refers to Foo pointers, so they can't both know each other's declaration. First question is whether it's safe (according to C++ spec, not in any given compiler) to cast a derived class pointer to its base class pointer type in the absence of a full definition of the derived class. Second question is whether there's a better approach. I'm aware I could move someMethod()'s body out of the class definition, but in this case it's important that it be inlined (part of an actual, measured hotspot - I'm not guessing).

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  • Perform separate compilation of Latex documents

    - by ancechu
    When compiling latex documents the compiler emits a lot of "object" files. This clutters the directories I'm working on and it difficults the use of VCS like SVN. When I work with C++ code I have separate directories for the code and the objects, I can run make on the source directory but the .o files go to the build directory. Is there a proper way to perform this separate compilation with Latex documents? Can it be done by using Makefiles or by passing options to the latex compiler? Thanks

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  • How do I get an Iterator over a vector of objects from a Template?

    - by nieldw
    I'm busy implementing a Graph ADT in C++. I have templates for the Edges and the Vertices. At each Vertex I have a vector containing pointers to the Edges that are incident to it. Now I'm trying to get an iterator over those edges. These are the lines of code: vector<Edge<edgeDecor, vertexDecor, dir>*> edges = this->incidentEdges(); vector<Edge<edgeDecor, vertexDecor, dir>*>::const_iterator i; for (i = edges.begin(); i != edges.end(); ++i) { However, the compiler won't accept the middle line. I'm pretty new to C++. Am I missing something? Why can't I declare an iterator over objects from the Edge template? The compiler isn't giving any useful feedback. Much thanks niel

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  • In a Linux user space process what is the address of the vsyscall page?

    - by TomMD
    I would like to acquire the address of the vsyscall page for my own uses. I only have two ideas here: alter the compiler to store this information in some known location after it is given to __start, or read /proc/[pid]/maps. I really don't want to read /proc/ as that is slow and shouldn't be necessary. I also don't want to make compiler modifications. Does anyone have an alternative? Is there a symbol I should know about? Its at the point I'm tempted to stuff this functionality into an ioctl call in a module I've developed as part of this work!

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  • Porting C++-code from Windows to Unix: systemcalls colliding with name of functions

    - by marvin2k
    Hi I'm porting some crufty C++ Windows-code to Linux, which uses functions called "open" and "close" inside every class... Very bad style, or? Luckily that wasn't a problem in windows, since their systemcalls are named different. When I try to call the systemcalls open() or close() I'm getting some compiler error about "no matching function for call for class:open()". I can't rename all our functions named "class::open" and "class::close" in the whole code, and I have to use open() and close() since I'm working with serial ports. So my question is: How can I tell the compiler, which open I mean? How can I escape or hide the namespace of a class in C++?

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  • Template inheritance: X is not a template

    - by user2923917
    I am trying to build a inheritance-structure which looks like: Base - template Grandpa - template Father class Base {}; template <int x> class Grandpa: public Base {}; template <int x> class Father: public Grandpa<x> {}; However, the compiler complains when compiling Father, that Grandpa is not a template. I guess it is just some synthatic issue, however everything I've tried so far led to even more compiler complaints ;) Any idea whats wrong?

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  • Passing a pointer to a function that doesn't match the requirements of the formal parameter

    - by Andreas Grech
    int valid (int x, int y) { return x + y; } int invalid (int x) { return x; } int func (int *f (int, int), int x, int y) { //f is a pointer to a function taking 2 ints and returning an int return f(x, y); } int main () { int val = func(valid, 1, 2), inval = func(invalid, 1, 2); // <- 'invalid' does not match the contract printf("Valid: %d\n", val); printf("Invalid: %d\n", inval); /* Output: * Valid: 3 * Invalid: 1 */ } At the line inval = func(invalid, 1, 2);, why am I not getting a compiler error? If func expects a pointer to a function taking 2 ints and I pass a pointer to a function that takes a single int, why isn't the compiler complaining? Also, since this is happening, what happens to the second parameter y in the invalid function?

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  • Visual Studio 2008 compiles anything in C++ file?

    - by Brad Pepers
    I noticed today that a source code file in a project was compiling even though it had junk at the top of it. It got me wondering what all would pass without error through the compiler. Here is an example of code that will not generate any error messages: what kind of weird behaviour is this??? #include "stdafx.h" // what is up? int foo(int bar) { bla bla bla????? return bar; } and more junk??? What in the world is the compiler doing to allow this code to compile without giving any error messages? I'm using Visual Studio 2008 and this is unmanaged C++ code. The foo function isn't actually generated in the object file so it can't be used but why no errors???

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  • VS2005 and VSS. Should .exes, .dlls, pdbs, .resource and generated .xml files go in VSS?

    - by Velika
    It seems like the following type of files need to be writable to be able to compile a solution. .exe .dll .pdb (if debugging) .resource (?) .xml (at least the system generated ones. I'm not sure if they are just all XML documentationf iles) If they were checked in and could only be overwritten by the compiler by the person who had them checked out, then checking them into sourcesafe and requiring a checkout to modify them, which is attemtped by the compiler each time you run, would interfer with other developer's ability to debug and run. What is the best practice? It seems like VSS automatically adds everything.

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  • Why is 'virtual' optional for overridden methods in derived classes?

    - by squelart
    When a method is declared as virtual in a class, its overrides in derived classes are automatically considered virtual as well, and the C++ language makes this keyword virtual optional in this case: class Base { virtual void f(); }; class Derived : public Base { void f(); // 'virtual' is optional but implied. }; My question is: What is the rationale for making virtual optional? I know that it is not absolutely necessary for the compiler to be told that, but I would think that developers would benefit if such a constraint was enforced by the compiler. E.g., sometimes when I read others' code I wonder if a method is virtual and I have to track down its superclasses to determine that. And some coding standards (Google) make it a 'must' to put the virtual keyword in all subclasses.

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  • Build multiple executables with small changes in objects

    - by Morgoth
    Consider the following Makefile COMP = compiler OBJECTS = file1 \ file2 \ file3 \ file4 \ file5_suffix \ file6 \ file7 \ file8 \ file9_suffix \ file10 all: $(OBJECTS) $(COMP) $(OBJECTS) -o bin/executable_suffix Is there an easy way to compile multiple executables for different values of suffix? For example, the equivalent of COMP = compiler OBJECTS1 = file1 \ file2 \ file3 \ file4 \ file5_s1 \ file6 \ file7 \ file8 \ file9_s1 \ file10 OBJECTS2 = file1 \ file2 \ file3 \ file4 \ file5_s2 \ file6 \ file7 \ file8 \ file9_s2 \ file10 all: $(OBJECTS1) $(OBJECTS2) $(COMP) $(OBJECTS1) -o bin/executable_s1 $(COMP) $(OBJECTS2) -o bin/executable_s2 but without redefining the whole list of objects? In the real life case I am dealing with, there might be 50+ objects and a dozen binaries to build, with only small changes between the object list each time, so it would be nice not to have to list all the objects each time.

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  • Is there a way to serialize automatically enums as int?

    - by FireAphis
    Hello, Is there a way to serialize enums automatically as int? Every time I define a new enum and write std::stringstream stream; stream << myenum1; stream >> myenum2; the compiler complains that the operators << and are not defined. Do you know a way to tell the compiler to treat enums as plain int's? What makes the problem harder is that, actually, the serialization is inside a template. Something like this: template <typename T> void serialize(const T& value) { std::stringstream stream; stream << value; } So I cannot add any casts :( Maybe I can specialize it somehow? Thank you.

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  • C++ packing a typdef enum

    - by Sagar
    typedef enum BeNeLux { BELGIUM, NETHERLANDS, LUXEMBURG } _PACKAGE_ BeNeLux; When I try to compile this with C++ Compiler, I am getting errors, but it seems to work fine with a C compiler. So here's the question. Is it possible to pack an enum in C++, or can someone see why I would get the error? The error is: "semicolon missing after declaration of BeNeLux". I know, after checking and rechecking, that there definitely is a semicolon there, and in any places required in the rest of the code.

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  • F#: Can't hide a type abbreviation in a signature? Why not?

    - by Nels Beckman
    In F#, I'd like to have what I see as a fairly standard Abstract Datatype: // in ADT.fsi module ADT type my_Type // in ADT.fs module ADT type my_Type = int In other words, code inside the module knows that my_Type is an int, but code outside does not. However, F# seems to have a restriction where type abbreviations specifically cannot be hidden by a signature. This code gives a compiler error, and the restriction is described here. If my_Type were instead a discriminated union, then there is no compiler error. My question is, why the restriction? I seem to remember being able to do this in SML and Ocaml, and furthermore, isn't this a pretty standard thing to do when creating an abstract datatype? Thanks

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  • [c++] How to create a std::ofstream to a temp file?

    - by dehmann
    Okay, mkstemp is the preferred way to create a temp file in POSIX. But it opens the file and returns an int, which is a file descriptor. From that I can only create a FILE*, but not an std::ofstream, which I would prefer in C++. (Apparently, on AIX and some other systems, you can create an std::ofstream from a file descriptor, but my compiler complains when I try that.) I know I could get a temp file name with tmpnam and then open my own ofstream with it, but that's apparently unsafe due to race conditions, and results in a compiler warning (g++ v3.4. on Linux): warning: the use of `tmpnam' is dangerous, better use `mkstemp' So, is there any portable way to create an std::ofstream to a temp file?

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  • Can you use #defined values in if statements (In C programs)?

    - by Jordan S
    I am new at C programming. I thought when you type something like #define Const 5000 that the compiler just replaces every instance of Const with 5000 at compile time. Is that wrong? I try doing this in my code and I get a syntax error. Why can't i do this? #define STEPS_PER_REV 12345 ... in some function if(CurrentPosition >= STEPS_PER_REV) { // do some stuff here } The compiler complains about the if statement with a syntax error that gives me no details.

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  • error C2065: 'AfxBeginThread' : undeclared identifier

    - by bdhar
    I have a simple ATL Service in which I have included the following statement. AfxBeginThread(WorkerThread, this, THREAD_PRIORITY_NORMAL, 0, 0); But the compiler complains that error C2065: 'AfxBeginThread' : undeclared identifier But in MSDN i found that AfxBeginThread is found in AFXWIN.H If I include AFXWIN.H, the compiler complains that fatal error C1189: #error : WINDOWS.H already included. MFC apps must not #include <windows.h> What am I missing here? Thanks. PS: I am using Visual Studio 6.0 Enterprise Edition in Windows XP SP2.

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  • C++ packing a typedef enum

    - by Sagar
    typedef enum BeNeLux { BELGIUM, NETHERLANDS, LUXEMBURG } _PACKAGE_ BeNeLux; When I try to compile this with C++ Compiler, I am getting errors, but it seems to work fine with a C compiler. So here's the question. Is it possible to pack an enum in C++, or can someone see why I would get the error? The error is: "semicolon missing after declaration of BeNeLux". I know, after checking and rechecking, that there definitely is a semicolon there, and in any places required in the rest of the code.

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  • Forward declaring an enum in c++

    - by szevvy
    Hi guys, I'm trying to do something like the following: enum E; void Foo(E e); enum E {A, B, C}; which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain? Many thanks. Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as enum E { FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X } as project X is not something I want my users to know about. So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people. As for the compiler - it's GCC.

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  • Inheritance and Implicit Type Casting

    - by Josué Molina
    Suppose I have the following three classes: class Animal {}; class Human : public Animal {}; class Dog : public Animal { public: void setOwner(Animal* owner) { this->owner = owner; } private: Animal* owner; }; Why is the following allowed, and what exactly is happening? Dog d; Human h; d.setOwner(&h); // ? At first, I tried to cast it like this d.setOwner(&(Animal)h), but the compiler gave me a warning, and I hit a run-time error. Edit: the warning the compiler gave me was "taking address of temporary". Why is this so?

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  • Setup Jetty 7 with JSP engine

    - by Justin
    I've been trying to get Jetty to run my web app via a custom launcher (embedded). I am trying to figure out how to tell Jetty which java compiler to use for JSPs. I want to do what java -jar start.jar -OPTIONS=jsp does, but without using start.jar. Here is what shows on the console: Javac exception, Unable to find a javac compiler; com.sun.tools.javac.Main is not on the classpath. Perhaps JAVA_HOME does not point to the JDK Do I need to put the javac libraries into my classpath?

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