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  • when is java faster than c++ (or when is JIT faster then precompiled)?

    - by kostja
    I have heard that under certain circumstances, Java programs or rather parts of java programs are able to be executed faster than the "same" code in C++ (or other precompiled code) due to JIT optimizations. This is due to the compiler being able to determine the scope of some variables, avoid some conditionals and pull similar tricks at runtime. Could you give an (or better - some) example, where this applies? And maybe outline the exact conditions under which the compiler is able to optimize the bytecode beyond what is possible with precompiled code? NOTE : This question is not about comparing Java to C++. Its about the possibilities of JIT compiling. Please no flaming. I am also not aware of any duplicates. Please point them out if you are.

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  • Can you make an incrementing compiler constant?

    - by Keith Nicholas
    While sounding nonsensical..... I want a Contant where every time you use it it will increment by 1 int x; int y; x = INCREMENTING_CONSTNAT; y = INCREMENTING_CONSTNAT; where x == 1; and y == 2 Note I don't want y = INCREMENTING_CONSTNAT+1 type solutions. Basically I want to use it as a compile time unique ID ( generally it wouldn't be used in code like the example but inside another macro)

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  • Why are forward declarations necessary?

    - by user199421
    In languages like C# and Java there is no need to declare (for example) a class before using it. If I understand it correctly this is because the compiler does two passes on the code. In the first it just "collects the information available" and in the second one it checks that the code is correct. In C and C++ the compiler does only one pass so everything needs to be available at that time. So my question basically is why isn't it done this way in C and C++. Wouldn't it eliminate the needs for header files?

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  • Protobuf compiler for several languages

    - by Stipa
    Hi, In my project I have components written on Python, ObjectiveC and J2ME. I want to use protobuf as data interchange format. However, there are one issue I need to resolve. Google implementation doesn't support ObjC and J2ME. There are 3rd party implementations that supports those languages. But I really don't want to be depended of several protoc implementations. What is the best way for me to have protobufs for several languages? Do I need to use different compilers or there is other option? Thanks, -Lev

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  • why optimization does not happen?

    - by aaa
    hi. I have C/C++ code, that looks like this: static int function(double *I) { int n = 0; // more instructions, loops, for (int i; ...; ++i) n += fabs(I[i] > tolerance); return n; } function(I); // return value is not used. compiler inlines function, however it does not optimize out n manipulations. I would expect compiler is able to recognize that value is never used as rhs only. Is there some side effect, which prevents optimization? Thanks

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  • C++ compiler unable to find function (namespace related)

    - by CS student
    I'm working in Visual Studio 2008 on a C++ programming assignment. We were supplied with files that define the following namespace hierarchy (the names are just for the sake of this post, I know "namespace XYZ-NAMESPACE" is redundant): (MAIN-NAMESPACE){ a bunch of functions/classes I need to implement... (EXCEPTIONS-NAMESPACE){ a bunch of exceptions } (POINTER-COLLECTIONS-NAMESPACE){ Set and LinkedList classes, plus iterators } } The MAIN-NAMESPACE contents are split between a bunch of files, and for some reason which I don't understand the operator<< for both Set and LinkedList is entirely outside of the MAIN-NAMESPACE (but within Set and LinkedList's header file). Here's the Set version: template<typename T> std::ostream& operator<<(std::ostream& os, const MAIN-NAMESPACE::POINTER-COLLECTIONS-NAMESPACE::Set<T>& set) Now here's the problem: I have the following data structure: Set A Set B Set C double num It's defined to be in a class within MAIN-NAMESPACE. When I create an instance of the class, and try to print one of the sets, it tells me that: error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const MAIN-NAMESPACE::POINTER-COLLECTIONS-NAMESPACE::Set' (or there is no acceptable conversion) However, if I just write a main() function, and create Set A, fill it up, and use the operator- it works. Any idea what is the problem? (note: I tried any combination of using and include I could think of).

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  • Controlling read and write access width to memory mapped registers in C

    - by srking
    I'm using and x86 based core to manipulate a 32-bit memory mapped register. My hardware behaves correctly only if the CPU generates 32-bit wide reads and writes to this register. The register is aligned on a 32-bit address and is not addressable at byte granularity. What can I do to guarantee that my C (or C99) compiler will only generate full 32-bit wide reads and writes in all cases? For example, if I do a read-modify-write operation like this: volatile uint32_t* p_reg = 0xCAFE0000; *p_reg |= 0x01; I don't want the compiler to get smart about the fact that only the bottom byte changes and generate 8-bit wide read/writes. Since the machine code is often more dense for 8-bit operations on x86, I'm afraid of unwanted optimizations. Disabling optimizations in general is not an option.

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  • How does compiling circular dependencies work?

    - by Fabio F.
    I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files. First, M.java: public class MType { XType x; MType() {x = null;} } Second, another file (in the same directory), XType.java: public class XType { MType m; public XType(MType m) {this.m = m;} } Ok it's bad programming, but if you run javac XType it compiles: compiles even MType because XType needs it. But ... MType needs XType ... how does that work? How does the compiler know what is happening? Probably this is a stupid question, but I would like to know how the compiler (javac or any other compilers you know) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.

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  • Trying to set up iPhone-gcc compiler

    - by Am4d
    So I've installed iPhone-gcc, make and ldid from cydia, i can't compile yet though because I don't have the headers setup. I've looked around and there's not really much info on setting up the headers, librarys and frameworks. I just need to know where to extract them from the sdk and where to place them on my iPhone. I've been trying to get this to work for a while, Any help would be great. Thanks Adam M

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  • How compiling circular dependencies works?

    - by Fabio F.
    I've made the example in Java but I think (not tested) that it works in other (all?) languages. You have 2 files M.java that says public class MType{ XType x; MType(){ x = null;} } and another file XType.java (in the same directory) public class XType{ MType m; public XType(MType m){ this.m=m;} } Ok it's BAD programming , but.. if you run javac XType it compiles: compiles even MTypes because XType needs it. But.. MType needs XType.. how it works? How does the compiler know what is happening? Probably is a stupid question, but I would like to know how the compiler (javac or other compilers if you know.) manages that situation, not how to avoid it. I'm asking because i'm writing a precompiler and I would like to manage that situation.. Thank you

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  • a newbie gcc compiler and c language question

    - by dydx
    Hi, when I'm trying to compile my c program it gives me this error warning: integer constant is too large for 'long' type which refers to these lines int barcode, a, b, c; scanf("%d", &barcode); a = barcode / 1000000000000; b = barcode / 100000000000 % 10; c = barcode / 10000000000 % 10; and the rest is fine. I know I'm not supposed to use int for such a large number, any suggestions on what I should use? if I replace int with double what should the '%d' part be replaced with then?

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  • Online compilers/runtime for Java, C++, Python and ObjC?

    - by Nocturne
    Does anyone know of a good online compiler/runtime (for C++, Java, Python, ObjC etc.) that I can access on the web? What I'm looking for is something that would allow me to type in a program in a web form and to run the program and see the results online. (Let's not get into the why for now. Suffice it to say for the moment that I don't always have access to a compiler/runtime, and firing up an IDE is just overkill for testing out some code snippets) I know of codepad.org -- but I'm looking for something better.

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  • Cannot understand the behaviour of dotnet compiler while instantiating a class thru interface(C#)

    - by Newbie
    I have a class that impelemnts an interface. The interface is public interface IRiskFactory { void StartService(); void StopService(); } The class that implements the interface is public class RiskFactoryService : IRiskFactory { } Now I have a console application and one window service. From the console application if I write the following code static void Main(string[] args) { IRiskFactory objIRiskFactory = new RiskFactoryService(); objIRiskFactory.StartService(); Console.ReadLine(); objIRiskFactory.StopService(); } It is working fine. However, when I mwrite the same piece of code in Window service public partial class RiskFactoryService : ServiceBase { IRiskFactory objIRiskFactory = null; public RiskFactoryService() { InitializeComponent(); objIRiskFactory = new RiskFactoryService(); <- ERROR } /// <summary> /// Starts the service /// </summary> /// <param name="args"></param> protected override void OnStart(string[] args) { objIRiskFactory.StartService(); } /// <summary> /// Stops the service /// </summary> protected override void OnStop() { objIRiskFactory.StopService(); } } It throws error: Cannot implicitly convert type 'RiskFactoryService' to 'IRiskFactory'. An explicit conversion exists (are you missing a cast?) When I type casted to the interface type, it started working objIRiskFactory = (IRiskFactory)new RiskFactoryService(); My question is why so? Thanks.(C#)

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  • Friendness and derived class

    - by ereOn
    Hi, Let's say I have the following class hierarchy: class Base { protected: virtual void foo() = 0; friend class Other; }; class Derived : public Base { protected: void foo() { /* Some implementation */ }; }; class Other { public: void bar() { Derived* a = new Derived(); a->foo(); // Compiler error: foo() is protected within this context }; }; I guess I could change it too a->Base::foo() but since foo() is pure virtual in the Base class, the call will result in calling Derived::foo() anyway. However, the compiler seems to refuse a->foo(). I guess it is logical, but I can't really understand why. Am I missing something ? Can't (shouldn't) it handle this special case ? Thank you.

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  • Bizarre C++ compiler problem

    - by Yassin
    Hi, I have the following C++ code: typedef istream_iterator<string> isi; // (1) vector<string> lineas(isi(cin), isi()); // (2) //vector<string> lineas; //copy(isi(cin), isi(), back_inserter(lineas)); typedef vector<string>::iterator vci; for (vci it = lineas.begin(); it != lineas.end(); ++it) cout &lt;&lt; *it &lt;&lt; endl; However, I get the error while compiling: test.cpp: In function 'int main(int, char**)': test.cpp:16: error: request for member 'begin' in 'lineas', which is of non-class type 'std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >(main(int, char**)::isi, main(int, char**)::isi (*)())' test.cpp:16: error: request for member 'end' in 'lineas', which is of non-class type 'std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >(main(int, char**)::isi, main(int, char**)::isi (*)())' However, if I replace (1) by (2), it compiles. I'm using g++ 4.4.0 What's wrong?

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  • Cannot understand the behaviour of C# compiler while instantiating a class thru interface

    - by Newbie
    I have a class that implements an interface. The interface is public interface IRiskFactory { void StartService(); void StopService(); } The class that implements the interface is public class RiskFactoryService : IRiskFactory { } Now I have a console application and one window service. From the console application if I write the following code static void Main(string[] args) { IRiskFactory objIRiskFactory = new RiskFactoryService(); objIRiskFactory.StartService(); Console.ReadLine(); objIRiskFactory.StopService(); } It is working fine. However, when I mwrite the same piece of code in Window service public partial class RiskFactoryService : ServiceBase { IRiskFactory objIRiskFactory = null; public RiskFactoryService() { InitializeComponent(); objIRiskFactory = new RiskFactoryService(); <- ERROR } /// <summary> /// Starts the service /// </summary> /// <param name="args"></param> protected override void OnStart(string[] args) { objIRiskFactory.StartService(); } /// <summary> /// Stops the service /// </summary> protected override void OnStop() { objIRiskFactory.StopService(); } } It throws error: Cannot implicitly convert type 'RiskFactoryService' to 'IRiskFactory'. An explicit conversion exists (are you missing a cast?) When I type cast to the interface type, it started working objIRiskFactory = (IRiskFactory)new RiskFactoryService(); My question is why so?

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  • CString a = "Hello " + "World!"; Is it possible?

    - by Sanctus2099
    I'm making my own string class and I was wondering if there's any way to replace the compiler behaviour around " characters. As I said in the title I'd like to make it so that CString a = "Hello " + "World!"; would actually work and not give a compiler error telling that it can't add 2 pointers. My string class automatically converts to char* when needed and thus writing printf(a) would not break the code. I'm sure this is a rather weird question but if it's possible I'd really like to know how to do it. Thank you very much

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  • Using Directives, Namespace and Assembly Reference - all jumbled up with StyleCop!

    - by Jack
    I like to adhere to StyleCop's formatting rules to make code nice and clear, but I've recently had a problem with one of its warnings: All using directives must be placed inside of the namespace. My problem is that I have using directives, an assembly reference (for mocking file deletion), and a namespace to juggle in one of my test classes: using System; using System.IO; using Microsoft.Moles.Framework; using Microsoft.VisualStudio.TestTools.UnitTesting; [assembly: MoledType(typeof(System.IO.File))] namespace MyNamespace { //Some Code } The above allows tests to be run fine - but StyleCop complains about the using directives not being inside the namespace. Putting the usings inside the namespace gives the error that "MoledType" is not recognised. Putting both the usings and the assembly reference inside the namespace gives the error 'assembly' is not a valid attribute location for this declaration. Valid attribute locations for this declaration are 'type'. All attributes in this block will be ignored. It seems I've tried every layout I can but to no avail - either the solution won't build, the mocking won't work or StyleCop complains! Does anyone know a way to set these out so that everything's happy? Or am I going to have to ignore the StyleCop warning in this case?

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