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• Is It Worth Using Bitwise Operators In Methods?

  - by user1626141

  I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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• C Structure Pointer Problem

  - by Halo

  I have this struct; #define BUFSIZE 10 struct shared_data { pthread_mutex_t th_mutex_queue; int count; int data_buffer_allocation[BUFSIZE]; int data_buffers[BUFSIZE][100]; }; and I want to allocate one of the data_buffers for a process, for that purpose I execute the following function; int allocate_data_buffer(int pid) { int i; for (i = 0; i < BUFSIZE; i++) { if (sdata_ptr->data_buffer_allocation[i] == NULL) { sdata_ptr->data_buffer_allocation[i] = pid; return i; } } return -1; } but the compiler warns me that I'm comparing pointer to a value. When I put a & in front of sdata_ptr it calms down but I'm not sure if it will work. Isn't what I wrote above supposed to be true?

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• C++ is there a difference between assignment inside a pass by value and pass by reference function?

  - by Rémy DAVID

  Is there a difference between foo and bar: class A { Object __o; void foo(Object& o) { __o = o; } void bar(Object o) { __o = o; } } As I understand it, foo performs no copy operation on object o when it is called, and one copy operation for assignment. Bar performs one copy operation on object o when it is called and another one for assignment. So I can more or less say that foo uses 2 times less memory than bar (if o is big enough). Is that correct ? Is it possible that the compiler optimises the bar function to perform only one copy operation on o ? i.e. makes __o pointing on the local copy of argument o instead of creating a new copy?

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• An easy way to replace fread()'s with reading from a byte array?

  - by Sam Washburn

  I have a piece of code that needs to be run from a restricted environment that doesn't allow stdio (Flash's Alchemy compiler). The code uses standard fopen/fread functions and I need to convert it to read from a char* array. Any ideas on how to best approach this? Does a wrapper exist or some library that would help? Thanks! EDIT: I should also mention that it's reading in structs. Like this: fread(&myStruct, 1, sizeof(myStruct), f);

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• C++: namespace conflict between extern "C" and class member

  - by plaisthos

  Hi, I stumbled upon a rather exotic c++ namespace problem: condensed example: extern "C" { void solve(lprec * lp); } class A { public: lprec * lp; void solve(int foo); } void A::solve(int foo) { solve(lp); } I want to call the c function solve in my C++ member function A::solve. The compiler is not happy with my intent: error C2664: 'lp_solve_ilp::solve' : cannot convert parameter 1 from 'lprec *' to 'int' Is there something I can prefix the solve function with? C::solve does not work

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• c++ when to put method out side the class

  - by user63898

  i saw that some times in c++ applications using only namespace declarations with header and source file like this : #ifndef _UT_ #define _UT_ #include <string> #include <windows.h> namespace UT { void setRootPath(char* program_path, char* file_path); char * ConvertStringToCharP(std::string str); }; #endif //and then in UT.cpp #include "UT.h" namespace UT { char * ConvertStringToCharP(std::string str) { char * writable = new char[str.size() + 1]; std::copy(str.begin(), str.end(), writable); writable[str.size()] = '\0'; return writable; } void setRootPath(char* program_path, char* file_path) { //... } } is it better then defining classic class with static methods? or just simple class ? dose this method has something better for the compiler linker ? the methods in this namespace are called allot of times .

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• What features of Scala cannot be translated to Java?

  - by Paul

  The Scala compiler compiles direct to Java byte code (or .NET CIL). Some of the features of Scala could be re-done in Java straightforwardly (e.g. simple for comprehensions, classes, translating anonymous/inner functionc etc). What are the features that cannot be translated that way? That is presumably mostly of academic interest. More usefully, perhaps, what are the key features or idioms of Scala that YOU use that cannot be easily represented in Java? Are there any the other way about? Things that can be done straightforwardly in Java that have no straightforward equivalent in Scala? Idioms in Java that don't translate?

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• Function calls in virtual machine killing performance

  - by GenTiradentes

  I wrote a virtual machine in C, which has a call table populated by pointers to functions that provide the functionality of the VM's opcodes. When the virtual machine is run, it first interprets a program, creating an array of indexes corresponding to the appropriate function in the call table for the opcode provided. It then loops through the array, calling each function until it reaches the end. Each instruction is extremely small, typically one line. Perfect for inlining. The problem is that the compiler doesn't know when any of the virtual machine's instructions are going to be called, as it's decided at runtime, so it can't inline them. The overhead of function calls and argument passing is killing the performance of my VM. Any ideas on how to get around this?

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• What is the explanation of this results in Java ?

  - by M.H

  I have the following code : public class Main { private int i = j; //1 private int j = 10; public static void main(String[] args) { System.out.println((new Main()).i); } } and there is a compiler error in line 1 because an illegal forward reference. But when I am trying the following code : public class Main { int i = getJ(); //1 int getJ(){ return j; } int j=10; public static void main(String[] args) { System.out.println(new Main().i); } } it works fine and the result is 0.Why there is no illegal forward reference in line 1 here?.The two codes look similar to me.

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• floats in NSArray

  - by JordanC

  I have an NSArray of floats which I did by encapsulating the floats using [NSNumber numberWithFloat:myFloat] ; Then I passed that array somewhere else and I need to pull those floats out of the array and perform basic arithmatic. When I try [myArray objectAtIndex:i] ; The compiler complains that I'm trying to perform arithmatic on a type id. It also won't let me cast to float or double. Any ideas? This seems like it should be an easy problem. Maybe it will come to me after another cup of coffee, but some help would be appreciated. Thanks.

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• Mono - Could not find a 'Sub Main' in ''

  - by lampej

  I started a new solution (with multiple projects) and am trying to get it to build. Initially I was getting an internal compiler error and thought maybe it had to do with MySql, so I removed all references to MySql. Now I am getting the error "Could not find a 'Sub Main' in ''". I have made sure that all of my projects have a Main subroutine like this: Public Shared Sub Main() End Sub 2 out of the 7 projects will compile. I don't know what makes these projects different from the others, and the error message isn't very helpful. Any experience with this one?

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• My Delphi 7 application halts on Application.Initialize and does not return to next line

  - by m-abdi

  I have created an application on Delphi 7. my app had running fine since yesterday. I don't know what's happened yesterday which cause my application halts on Application.Initialize line in source code and does not return to next line when i trace the program. I can't run the created executable file from widows niether while the generated file does run on another machine correctly. here is the code where the compiler stops on it: program Info_Kiosk; uses SysUtils, Forms, ... (some other units) ; {$R *.res} begin Application.Initialize; Application.CreateForm(Tfrm_Main, frm_Main); any help would be appreciated

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• "Socket operation on non-socket" error due to strange sytax

  - by Robert S. Barnes

  I ran across the error Socket operation on non-socket in some of my networking code when calling connect and spent a lot of time trying to figure out what was causing it. I finally figured out that the following line of code was causing the problem: if ((sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol) < 0)) { See the problem? Here's what the line should look like: if ((sockfd = socket( ai->ai_family, ai->ai_socktype, ai->ai_protocol)) < 0) { What I don't understand is why the first, incorrect line doesn't produce a warning. To put it another way, shouldn't the general form: if ( foo = bar() < baz ) do_somthing(); look odd to the compiler, especially running with g++ -Wall -Wextra? If not, shouldn't it at least show up as "bad style" to cppcheck, which I'm also running as part of my compile?

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• dropdown list selected index changed

  - by KareemSaad

  I did my drop down list that get it,s values from database and when run the application it didnot work and compiler didnot see the code onselectedindexchanged="DDlProductFamily_SelectedIndexChanged" protected void DDlProductFamily_SelectedIndexChanged(object sender, EventArgs e) { using (SqlConnection Con = Connection.GetConnection()) { SqlCommand Com = new SqlCommand("SelectThumbByProductFamily", Con); Com.CommandType = CommandType.StoredProcedure; Com.Parameters.Add(Parameter.NewInt("@ProductCategory_Id", DDlProductFamily.SelectedValue.ToString())); SqlDataAdapter DA = new SqlDataAdapter(Com); DA.Fill(dt); DataList1.DataSource = dt; DataList1.DataBind(); } }

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• Pointer to a C++ class member function as a global function's parameter?

  - by marcin1400

  I have got a problem with calling a global function, which takes a pointer to a function as a parameter. Here is the declaration of the global function: int lmdif ( minpack_func_mn fcn, void *p, int m, int n, double *x, double *fvec, double ftol) The "minpack_func_mn" symbol is a typedef for a pointer to a function, defined as: typedef int (*minpack_func_mn)(void *p, int m, int n, const double *x, double *fvec, int iflag ); I want to call the "lmdif" function with a pointer to a function which is a member of a class I created, and here is the declaration of this class function: int LT_Calibrator::fcn(void *p, int m, int n, const double *x, double *fvec,int iflag) I am calling a global function like this: info=lmdif(&LT_Calibrator::fcn, 0, m, n, x, fvec, ftol) Unfortunately, I get a compiler error, which says: "error C2664: 'lmdif' : cannot convert parameter 1 from 'int (__thiscall LT_Calibrator::* )(void *,int,int,const double *,double *,int)' to 'minpack_func_mn' 1 There is no context in which this conversion is possible" Is there any way to solve that problem?

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• C++: namespace conflicht between extern "C" and class member

  - by plaisthos

  Hi, I stumbled upon a rather exotic c++ namespace problem: condensed example: extern "C" { void solve(lprec * lp); } class A { public: lprec * lp; void solve(int foo); } void A::solve(int foo) { solve(lp); } I want to call the c funcition solve in my C++ member function A::solve. The compiler is not happy with my intents: error C2664: 'lp_solve_ilp::solve' : cannot convert parameter 1 from 'lprec *' to 'int' Is there something I can prefix the solve function? C::solve does not work

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• How can I do these operations in C?

  - by Juan Antonio

  Hello, I'm converting some assembly code to C to be able to use it with the current compiler environment I have to work with. I've reached 2 operations I don't know how to translate to C. Anyone know how to do it? In both, offset is an unsigned 32-bit integer and shift is a signed integer value. C_FLAG is a bool. OP1: __asm { __asm mov ecx, shift __asm ror offset, cl } OP2: __asm { __asm bt dword ptr C_FLAG, 0 __asm rcr offset, 1 } Thank you very much for your expertise. P.S.: I'm not the original developer, nor I have seen many x86 assembly code...

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• Problem with basic program using Boost Threads in c++

  - by Eternal Learner

  I have a simple program which creates and executes as thread using boost threads in c++. #include<boost/thread/thread.hpp> #include<iostream> void hello() { std::cout<<"Hello, i am a thread"<<std::endl; } int main() { boost::thread th1(&hello); th1.join(); } The compiler throws an error against the th1.join() line. It says " Multiple markers at this line - undefined reference to `boost::thread::join()' - undefined reference to `boost::thread::~thread()' "

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• When will YOU adopt C++0x?

  - by HighCommander4

  I'm particularly looking for input from managers of ongoing C++ projects: Have you already adopted C++0x? If so, what has your experience been like? If you haven't adopted C++0x yet, are you planning to? If so, what is your timeline (in rough terms)? Are there any obstacles that are holding you back from adopting C++0x? Perhaps you are waiting for your favourite compiler or IDE to catch up? For managers of open source projects: are you afraid that adopting C++0x will mean less developers who are willing/able to contribute because they don't know the new features? Or, on the other hand, do you think most developers have been eagerly awaiting C++0x, and and will jump at the opportunity to use it? Do you think C++0x is stable enough to be adopted by a large project?

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• Injecting a dependancy into a base class

  - by Jamie Dixon

  Hey everyone, I'm on a roll today with questions. I'm starting out with Dependency Injection and am having some trouble injecting a dependency into a base class. I have a BaseController controller which my other controllers inherit from. Inside of this base controller I do a number of checks such as determining if the user has the right privileges to view the current page, checking for the existence of some session variables etc. I have a dependency inside of this base controller that I'd like to inject using Ninject however when I set this up as I would for my other dependencies I'm told by the compiler that: Error 1 'MyProject.Controllers.BaseController' does not contain a constructor that takes 0 argument This makes sense but I'm just not sure how to inject this dependency. Should I be using this pattern of using a base controller at all or should I be doing this in a more efficient/correct way?

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• How can I force the text go to the button of the panel?

  - by Roman

  At the moment I have the following code which works fine. label = new JLabel(panelLabel,SwingConstants.CENTER); outputPanel.add(label,BorderLayout.CENTER); I get the text in the center of the panel (in terms of the left-right position as well as in terms of the top-bottom). Now I want to set the position to the bottom (and center in terms of "left-right"). I tried to use SOUTH instead of the CENTER in the first line. Compiler does not complains but during the execution i get IllegalArgumentException: HorizontalAlignment. What is that?

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• Using typedefs (or #defines) on built in types - any sensible reason?

  - by jb

  Well I'm doing some Java - C integration, and throught C library werid type mappings are used (theres more of them;)): #define CHAR char /* 8 bit signed int */ #define SHORT short /* 16 bit signed int */ #define INT int /* "natural" length signed int */ #define LONG long /* 32 bit signed int */ typedef unsigned char BYTE; /* 8 bit unsigned int */ typedef unsigned char UCHAR; /* 8 bit unsigned int */ typedef unsigned short USHORT; /* 16 bit unsigned int */ typedef unsigned int UINT; /* "natural" length unsigned int*/ Is there any legitimate reason not to use them? It's not like char is going to be redefined anytime soon. I can think of: Writing platform/compiler portable code (size of type is underspecified in C/C++) Saving space and time on embedded systems - if you loop over array shorter than 255 on 8bit microprocessor writing: for(uint8_t ii = 0; ii < len; ii++) will give meaureable speedup.

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• Masking a bit in C returning unexpected result

  - by Eamorr

  0x7F000000 is 0111 1111 0000 0000 0000 0000 0000 0000 in 32 bit binary. 0x01000058 is 0000 0001 0000 0000 0000 0000 0101 1000. When I AND the two numbers together I expect 0000 0001 0000 0000 0000 0000 0000 0000, but for some reason I get 0. Here is my code: #define MASK_binop 0x80000000 #define MASK_operation 0x7F000000 int instruction=atoi(line); if((MASK_binop & instruction)>0) printf("binop\n"); else if((MASK_operation & instruction)>0) printf("operation\n"); Each of the above comparisons keeps returning zero. Is it something to do with 32/64 bits? I'm using 64-bit compiler.

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• Memory management for "id<ProtocolName> variableName" type properties

  - by Malakim

  Hi, I'm having a problem with properties of the following type: id<ProtocolName> variableName; ..... ..... @property (nonatomic, retain) id<ProtocolName> variableName; I can access and use them just fine, but when I try to call [variableName release]; I get compiler warnings: '-release' not found in protocol(s) Do I need to define a release method in the interface, or how do I release the memory reserved for the variable? Thanks!

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• What's the best way to build software that doesn't require the newest glibc?

  - by ZorbaTHut

  I'm attempting to build a binary package that can be run on multiple Linux distributions. It's currently built on Ubuntu 10.04, but it fails on Ubuntu 8.04 with the following error: ./test: /usr/lib/libstdc++.so.6: version `GLIBCXX_3.4.11' not found (required by ./test) ./test: /usr/lib/libstdc.so.6: version `GLIBC_2.11' not found (required by ./test) What's the preferred way to solve this problem? Is there a way to install an old glibc on a new box and build against it, or do I have to build on an old distribution? And if I build against an old glibc, will it work on a new glibc? Or, alternatively, are there just some handy compiler flags or packages I could install to solve the problem?

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