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  • How does virtual inheritance solve the diamond problem?

    - by cambr
    class A { public: void eat(){ cout<<"A";} }; class B: virtual public A { public: void eat(){ cout<<"B";} }; class C: virtual public A { public: void eat(){ cout<<"C";} }; class D: public B,C { public: void eat(){ cout<<"D";} }; int main(){ A *a = new D(); a->eat(); } I understand the diamond problem, and above piece of code does not have that problem. How exatly does virtual inheritance solve the problem? What I understand: When I say A *a = new D();, the compiler wants to know if an object of type D can be assigned to a pointer of type A, but it has two paths that it can follow, but cannot decide by itself. So, how does virtual inheritance resolve the issue (help compiler take the decision)?

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  • Modifying a const through a non-const pointer

    - by jasonline
    I'm a bit confused what happened in the following code: const int e = 2; int* w = ( int* ) &e; // (1) cast to remove const-ness *w = 5; // (2) cout << *w << endl; // (3) outputs 5 cout << e << endl; // (4) outputs 2 cout << "w = " << w << endl; // (5) w points to the address of e cout << "&e = " << &e << endl; In (1), w points to the address of e. In (2), that value was changed to 5. However, when the values of *w and e were displayed, their values are different. But if you print value of w pointer and &e, they have the same value/address. How come e still contained 2, even if it was changed to 5? Were they stored in a separate location? Or a temporary? But how come the value pointed by w is still the address of e?

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  • Keybd is not working right =(

    - by user302131
    i can't get this to work right this should press left for 1sec then wait 10secs then right 1sec. keybd_event(0x25, 0xCB, 0, 0); // press left cout << "Ldown\n"; // so i know it worked Sleep(1000); // hold it for 1sec keybd_event(0x25, 0xCB, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Lup\n"; // so i know i let go Sleep(10000); // Sleep for 10secs keybd_event(0x27, 0xCD, 0, 0); // press right cout << "Rdown\n"; // so i know i pressed right Sleep(1000); // sleep 1sec keybd_event(0x27, 0xCD, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Rdown\n"; // so i know i let go. this is in a loop but it wont do anything :( unless i close the program before the key is let go then it will just keep the keydown until i press the key again. i know you can use only one key code if you want but i need to use both. so what i'm i missing?

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  • How to simulate inner exception in C++

    - by Siva Chandran
    Basically I want to simulate .NET Exception.InnerException in C++. I want to catch exception from bottom layer and wrap it with another exception and throw again to upper layer. The problem here is I don't know how to wrap the catched exception inside another exception. struct base_exception : public std::exception { std::exception& InnerException; base_exception() : InnerException(???) { } // <---- what to initialize with base_exception(std::exception& innerException) : InnerException(innerException) { } }; struct func1_exception : public base_exception { const char* what() const throw() { return "func1 exception"; } }; struct func2_exception : public base_exception { const char* what() const throw() { return "func2 exception"; } }; void func2() { throw func2_exception(); } void func1() { try { func2(); } catch(std::exception& e) { throw func2_exception(e); // <--- is this correct? will the temporary object will be alive? } } int main(void) { try { func1(); } catch(base_exception& e) { std::cout << "Got exception" << std::endl; std::cout << e.what(); std::cout << "InnerException" << std::endl; std::cout << e.InnerException.what(); // <---- how to make sure it has inner exception ? } } In the above code listing I am not sure how to initialize the "InnerException" member when there is no inner exception. Also I am not sure whether the temporary object that is thrown from func1 will survive even after func2 throw?

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  • how is data stored at bit level according to "Endianness" ?

    - by bakra
    I read about Endianness and understood squat... so I wrote this main() { int k = 0xA5B9BF9F; BYTE *b = (BYTE*)&k; //value at *b is 9f b++; //value at *b is BF b++; //value at *b is B9 b++; //value at *b is A5 } k was equal to "A5 B9 BF 9F" and (byte)pointer "walk" o/p was "9F BF b9 A5" so I get it bytes are stored backwards...ok. ~ so now I thought how is it stored at BIT level... I means is "9f"(1001 1111) stored as "f9"(1111 1001)? so I wrote this int _tmain(int argc, _TCHAR* argv[]) { int k = 0xA5B9BF9F; void *ptr = &k; bool temp= TRUE; cout<<"ready or not here I come \n"< for(int i=0;i<32;i++) { temp = *( (bool*)ptr + i ); if( temp ) cout<<"1 "; if( !temp) cout<<"0 "; if(i==7||i==15||i==23) cout<<" - "; } } I get some random output even for nos. like "32" I dont get anything sensible. why ?

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  • string Comparison

    - by muhammad-aslam
    I want to compare two user input strings, but not able to do so... #include "stdafx.h" #include "iostream" #include "string" using namespace std; int _tmain(int argc, _TCHAR* argv0[]) { string my_string; string my_string2; cout<<"Enter string"<<endl; cin>>my_string; cout<<"Enter 2nd string"<<endl; cin>>my_string2; cout<<my_string<<" "<<my_string2; strcmp(my_string,my_string2); int result; result= strcmp(my_string,my_string2); cout<<result<<endl; return 0; } This error is appearing. Error 1 error C2664: 'strcmp' : cannot convert parameter 1 from 'std::string' to 'const char *' c:\users\asad\documents\visual studio 2008\projects\string\string\string.cpp 23 String

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  • C++: Is there any good way to read/write without specifically stating character type in function nam

    - by Mark L.
    I'm having a problem getting a program to read from a file based on a template, for example: bool parse(basic_ifstream<T> &file) { T ch; locale loc = file.getloc(); basic_string<T> buf; file.unsetf(ios_base::skipws); if (file.is_open()) { while (file >> ch) { if(isalnum(ch, loc)) { buf += ch; } else if(!buf.empty()) { addWord(buf); buf.clear(); } } if(!buf.empty()) { addWord(buf); } return true; } return false; } This will work when I instantiate this class with <char>, but has problems when I use <wchar_t> (clearly). Outside of the class, I'm using: for (iter = mp.begin(); iter != mp.end(); ++iter ) { cout << iter->first << setw(textwidth - iter->first.length() + 1); cout << " " << iter->second << endl; } To write all of the information from this data struct (it's a map<basic_string<T>, int>), and as predicted, cout explodes if iter->first isn't a char array. I've looked online and the consensus is to use wcout, but unfortunately, since this program requires that the template can be changed at compile time (<char> - <wchar_t>) I'm not sure how I could get away with simply choosing cout or wcout. That is, unless there way a way to read/write wide characters without changing lots of code. If this explanation sounds awkwardly complicated, let me know and I'll address it as best I can.

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  • Strange casting problem with tm structure

    - by egiakoum1984
    I have the following casting problem when my data structure sSpecificData contains a field of type tm: typedef struct { unsigned char data[10000]; } sDataBuffer; typedef struct { int m_Id; sDataBuffer m_Data; } sData; typedef struct { int m_value1; int m_value2; tm m_Date; } sSpecificData; const int SPECIFIC_SVC_DATA_SIZE = sizeof(sSpecificData); typedef struct { int m_Id; sSpecificData m_Data; } sMyData; int main(void) { sData svc; sMyData* ptr1 = (sMyData*) &svc; sSpecificData* ptr2; ptr2 = (sSpecificData*) &svc.m_Data; ptr1->m_Data.m_value1 = 90; ptr1->m_Data.m_value2 = 80; cout << ptr1->m_Data.m_value1 << endl; cout << ptr1->m_Data.m_value2 << endl; cout << ptr2->m_value1 << endl; cout << ptr2->m_value2 << endl; return 0; } Without the field "tm m_Date;" as part of the sSpecificData, the output is correct: 90 80 90 80 With the field "tm m_Date;" as part of the sSpecificData, the output is wrong: 90 80 0 <-- ! 90 <-- ! Is there any idea why my example doesn't work when there is field of type tm as part of the sSpecificData? Thanks!

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  • "Unable to open file", when the program tries to open file in /proc

    - by tristartom
    Hi, I try to read file /proc/'pid'/status, using c program. The code is as follows, and even I use sudo to run it, the prompt still keeps throwing "Unable to open file". Please let me know if you have any ideas on how to fix this. thanks Richard ... int main (int argc, char* argv[]) { string line; char* fileLoc; if(argc != 2) { cout << "a.out file_path" << endl; fileLoc = "/proc/net/dev"; } else { sprintf(fileLoc, "/proc/%d/status", atoi(argv[1])); } cout<< fileLoc << endl; ifstream myfile (fileLoc); if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; } myfile.close(); } else cout << "Unable to open file"; return 0; }

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  • determining True/False.

    - by sil3nt
    Hi there, the following code #include <iostream> using namespace std; int main(){ char greeting[50] = "goodmorning everyone"; char *s1 = greeting; char *s2 = &greeting[7]; bool test = s2-s1; cout << "s1 is: " << s1 << endl; cout << "s2 is: " << s2 << endl; if (test == true ){ cout << "test is true and is: " << test << endl; } if (test == false){ cout<< "test is false and is: " << test << endl; } return 0; } outputs: s1 is: goodmorning everyone s2 is: ning everyone test is true and is: 1 here what does the line bool test = s2-s1; actually evaluate?, is it the length of the string?. If so, then seeing as s2 is a smaller than s1 it should be negative correct?, and yet the output is true?. Also if i change it to bool test = s1-s2; I still end up with the same result. So it doesnt matter whether its negative or positive the it will be true? and only false when 0?. what does the s2-s1 mean? -cheers (trying to get rid of doubts:))

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  • What is difference between my atoi() calls?

    - by Lucas
    I have a big number stored in a string and try to extract a single digit. But what are the differences between those calls? #include <iostream> #include <string> int main(){ std::string bigNumber = "93485720394857230"; char tmp = bigNumber.at(5); int digit = atoi(&tmp); int digit2 = atoi(&bigNumber.at(5)) int digit3 = atoi(&bigNumber.at(12)); std::cout << "digit: " << digit << std::endl; std::cout << "digit2: " << digit2 << std::endl; std::cout << "digit3: " << digit3 << std::endl; } This will produce the following output. digit: 7 digit2: 2147483647 digit3: 57230 The first one is the desired result. The second one seems to me to be a random number, which I cannot find in the string. The third one is the end of the string, but not just a single digit as I expected, but up from the 12th index to the end of the string. Can somebody explain the different outputs to me? EDIT: Would this be an acceptable solution? char tmp[2] = {bigNumber.at(5), '\0'}; int digit = atoi(tmp); std::cout << "digit: " << digit << std::endl;

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  • Throwing a C++ exception after an inline-asm jump

    - by SoapBox
    I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call. But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work. How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally? The code: #include <iostream> #include <stdexcept> using namespace std; void thrower() { cout << "Inside thrower" << endl; throw runtime_error("some exception"); } int main() { cout << "Top of main" << endl; try { asm volatile ( "jmp *%0" // same thing happens with a call instead of a jmp : : "r"((long)thrower) : ); } catch (exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The expected output: Top of main Inside thrower Caught : some exception Bottom of main The actual output: Top of main Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): some exception Aborted

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  • Constructor or Assignment Operator

    - by ju
    Can you help me is there definition in C++ standard that describes which one will be called constructor or assignment operator in this case: #include <iostream> using namespace std; class CTest { public: CTest() : m_nTest(0) { cout << "Default constructor" << endl; } CTest(int a) : m_nTest(a) { cout << "Int constructor" << endl; } CTest(const CTest& obj) { m_nTest = obj.m_nTest; cout << "Copy constructor" << endl; } CTest& operatorint rhs) { m_nTest = rhs; cout << "Assignment" << endl; return *this; } protected: int m_nTest; }; int _tmain(int argc, _TCHAR* argv[]) { CTest b = 5; return 0; } Or is it just a matter of compiler optimization?

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  • Constructor and Destructors in C++ [Not a question] [closed]

    - by Jack
    I am using gcc. Please tell me if I am wrong - Lets say I have two classes A & B class A { public: A(){cout<<"A constructor"<<endl;} ~A(){cout<<"A destructor"<<endl;} }; class B:public A { public: B(){cout<<"B constructor"<<endl;} ~B(){cout<<"B destructor"<<endl;} }; 1) The first line in B's constructor should be a call to A's constructor ( I assume compiler automatically inserts it). Also the last line in B's destructor will be a call to A's destructor (compiler does it again). Why was it built this way? 2) When I say A * a = new B(); compiler creates a new B object and checks to see if A is a base class of B and if it is it allows 'a' to point to the newly created object. I guess that is why we don't need any virtual constructors. ( with help from @Tyler McHenry , @Konrad Rudolph) 3) When I write delete a compiler sees that a is an object of type A so it calls A's destructor leading to a problem which is solved by making A's destructor virtual. As user - Little Bobby Tables pointed out to me all destructors have the same name destroy() in memory so we can implement virtual destructors and now the call is made to B's destructor and all is well in C++ land. Please comment.

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  • C++ Numerical truncation error

    - by Andrew
    Hello everyone, sorry if dumb but could not find an answer. #include <iostream> using namespace std; int main() { double a(0); double b(0.001); cout << a - 0.0 << endl; for (;a<1.0;a+=b); cout << a - 1.0 << endl; for (;a<10.0;a+=b); cout << a - 10.0 << endl; cout << a - 10.0-b << endl; return 0; } Output: 0 6.66134e-16 0.001 -1.03583e-13 Tried compiling it with MSVC9, MSVC10, Borland C++ 2010. All of them arrive in the end to the error of about 1e-13. Is it normal to have such a significant error accumulation over only a 1000, 10000 increments?

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  • Why do not C++11's move constructor/assignment operator act as expected

    - by xmllmx
    #include <iostream> using namespace std; struct A { A() { cout << "A()" << endl; } ~A() { cout << "~A()" << endl; } A(A&&) { cout << "A(A&&)" << endl; } A& operator =(A&&) { cout << "A& operator =(A&&)" << endl; return *this; } }; struct B { // According to the C++11, the move ctor/assignment operator // should be implicitly declared and defined. The move ctor // /assignment operator should implicitly call class A's move // ctor/assignment operator to move member a. A a; }; B f() { B b; // The compiler knows b is a temporary object, so implicitly // defined move ctor/assignment operator of class B should be // called here. Which will cause A's move ctor is called. return b; } int main() { f(); return 0; } My expected output should be: A() A(A&&) ~A() ~A() However, the actual output is: (The C++ compiler is: Visual Studio 2012) A() ~A() ~A() Is this a bug of VC++? or just my misunderstanding?

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  • Need feedback on two member functions of a Table class in C++

    - by George
    int Table::addPlayer(Player player, int position) { deque<Player>::iterator it = playerList.begin()+position; deque<Player>::iterator itStart = playerList.begin()+postion; while(*it != "(empty seat)") { it++; if (it == playerList.end()) { it = playerList.begin(); } if (it == itStart) { cout << "Table full" << endl; return -1; } } //TODO overload Player assignment, << operator *it = player; cout << "Player " << player << " sits at position " << it - playerList.begin() << endl; return it - playerList.begin(); } } int Table::removePlayer(Player player) { deque<Player>::iterator it = playerList.begin(); //TODO Do I need to overload != in Player? while(*it != player) { it++; if (it == playerList.end()) { cout << "Player " << player << " not found" << endl; return -1; } } *it = "(empty seat)"; cout << "Player " << player << " stands up from position " << it - playerList.begin() << endl; return it - playerList.begin(); } Would like some feedback on these two member functions of a Table class for Texas Hold Em Poker simulation. Any information syntax, efficiency or even common practices would be much appreciated.

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  • Class Assignment Operators

    - by Maxpm
    I made the following operator overloading test: #include <iostream> #include <string> using namespace std; class TestClass { string ClassName; public: TestClass(string Name) { ClassName = Name; cout << ClassName << " constructed." << endl; } ~TestClass() { cout << ClassName << " destructed." << endl; } void operator=(TestClass Other) { cout << ClassName << " in operator=" << endl; cout << "The address of the other class is " << &Other << "." << endl; } }; int main() { TestClass FirstInstance("FirstInstance"); TestClass SecondInstance("SecondInstance"); FirstInstance = SecondInstance; SecondInstance = FirstInstance; return 0; } The assignment operator behaves as-expected, outputting the address of the other class. Now, how would I actually assign something from the other class? For example, something like this: void operator=(TestClass Other) { ClassName = Other.ClassName; }

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  • keybd_event is not working right =(

    - by user302131
    I can't get this to work right. This should press left for 1 second then wait 10 seconds, then right 1 second, etc.: keybd_event(0x25, 0xCB, 0, 0); // press left cout << "Ldown\n"; // so i know it worked Sleep(1000); // hold it for 1sec keybd_event(0x25, 0xCB, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Lup\n"; // so i know i let go Sleep(10000); // Sleep for 10secs keybd_event(0x27, 0xCD, 0, 0); // press right cout << "Rdown\n"; // so i know i pressed right Sleep(1000); // sleep 1sec keybd_event(0x27, 0xCD, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Rdown\n"; // so i know i let go. This is in a loop but it wont do anything :( Unless I close the program before the key is let go, then it will just keep the key down until I press the key again. I know you can use only one key code if you want but I need to use both. So what am I missing?

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  • Programming help Loop adding

    - by Deonna
    I know this probably really simple but Im not sure what im doing wrong... The assignment states: For the second program for this lab, you are to have the user enter an integer value in the range of 10 to 50. You are to verify that the user enters a value in that range, and continue to prompt him until he does give you a value in that range. After the user has successfully entered a value in that range, you are to display the sum of all the integers from 1 to the value entered. I have this so far: #include <iostream.h> int main () { int num, sum; cout << "do-while Loop Example 2" << endl << endl; do { cout << "Enter a value from 10 to 50: "; cin >> num; if (num < 10 || num > 50) cout << "Out of range; Please try again..." << endl; } while (num < 10 || num > 50); { int i; int sum = 0; for (num = 1; num <= 50; num ++) sum = sum + num; } cout << endl << "The sum is " << sum << endl; return 0; } Im just not sure exactly what i'm doing wrong... I keep getting the wrong sum for the total...

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  • C++ STL type_traits question.

    - by Kim Sun-wu
    I was watching the latest C9 lecture and noticed something interesting.. In his introduction to type_traits, Stephan uses the following (as he says, contrived) example: template <typename T> void foo(T t, true_type) { std::cout << t << " is integral"; } template <typename T> void foo(T t, false_type) { std::cout << t << " is not integral"; } template <typename T> void bar(T t) { foo(t, typename is_integral<T>::type()); } This seems to be far more complicated than: template <typename T> void foo(T t) { if(std::is_integral<T>::value) std::cout << "integral"; else std::cout << "not integral"; } Is there something wrong with the latter way of doing it? Is his way better? Why? Thanks.

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  • Question about Virtual Inheritance hierarchy

    - by Summer_More_More_Tea
    Hi there: I encounter this problem when tackling with virtual inheritance. I remember that in a non-virtual inheritance hierarchy, object of sub-class hold an object of its direct super-class. What about virtual inheritance? In this situation, does object of sub-class hold an object of its super-class directly or just hold a pointer pointing to an object of its super-class? By the way, why the output of the following code is: sizeof(A): 8 sizeof(B): 20 sizeof(C): 20 sizeof(C): 36 Code: #include <iostream> using namespace std; class A{ char k[ 3 ]; public: virtual void a(){}; }; class B : public virtual A{ char j[ 3 ]; public: virtual void b(){}; }; class C : public virtual B{ char i[ 3 ]; public: virtual void c(){}; }; class D : public B, public C{ char h[ 3 ]; public: virtual void d(){}; }; int main( int argc, char *argv[] ){ cout << "sizeof(A): " << sizeof( A ) << endl; cout << "sizeof(B): " << sizeof( B ) << endl; cout << "sizeof(C): " << sizeof( C ) << endl; cout << "sizeof(D): " << sizeof( D ) << endl; return 0; } Thanks in advance. Kind regards.

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  • C++ function overloading and dynamic binding compile problem

    - by Olorin
    #include <iostream> using namespace std; class A { public: virtual void foo(void) const { cout << "A::foo(void)" << endl; } virtual void foo(int i) const { cout << i << endl; } virtual ~A() {} }; class B : public A { public: void foo(int i) const { this->foo(); cout << i << endl; } }; class C : public B { public: void foo(void) const { cout << "C::foo(void)" << endl; } }; int main(int argc, char ** argv) { C test; test.foo(45); return 0; } The above code does not compile with: $>g++ test.cpp -o test.exe test.cpp: In member function 'virtual void B::foo(int) const': test.cpp:17: error: no matching function for call to 'B::foo() const' test.cpp:17: note: candidates are: virtual void B::foo(int) const test.cpp: In function 'int main(int, char**)': test.cpp:31: error: no matching function for call to 'C::foo(int)' test.cpp:23: note: candidates are: virtual void C::foo() const It compiles if method "foo(void)" is changed to "goo(void)". Why is this so? Is it possible to compile the code without changing the method name of "foo(void)"? Thanks.

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  • c++ issues with cin.fail() in my program

    - by Wallace
    I want to use input y to do saving thing,and r to do resuming, but then i write it in the following codes,and then I input y or r,I just to be noticed ""Please enter two positve numbers" this line code "if(x==(int)('y'))"and next line is ignored.how could this happen int main(){ cout<<"It's player_"<<player+1<<"'s turn please input a row and col,to save and exit,input 0,resume game input"<<endl; while(true){ cin>>x; if(x==(int)('y')) {save();has_saved=true;break;} if(x==(int)('r')) {resume();has_resumed=true;break;} cin>>y; if(cin.fail()){ cout<<"Please enter two positve numbers"<<endl; cin.clear(); cin.sync();} else if (x>n||x<1||y<1||y>n) { cout<<"your must input a positive number less or equal than "<<n<<endl; continue;} else if(chessboard[x][y]!=' ') {cout<<"Wrong input please try again!"<<endl; continue;} else { chessboard[x][y]=player_symbol[player+1]; break; } } }

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  • display multiple errors via bool flag c++

    - by igor
    Been a long night, but stuck on this and now am getting "segmentation fault" in my compiler.. Basically I'm trying to display all the errors (the cout) needed. If there is more than one error, I am to display all of them. bool validMove(const Square board[BOARD_SIZE][BOARD_SIZE], int x, int y, int value) { int index; bool moveError = true; const int row_conflict(0), column_conflict(1), grid_conflict(2); int v_subgrid=x/3; int h_subgrid=y/3; getCoords(x,y); for(index=0;index<9;index++) if(board[x][index].number==value){ cout<<"That value is in conflict in this row\n"; moveError=false; } for(index=0;index<9;index++) if(board[index][y].number==value){ cout<<"That value is in conflict in this column\n"; moveError=false; } for(int i=v_subgrid*3;i<(v_subgrid*3 +3);i++){ for(int j=h_subgrid*3;j<(h_subgrid*3+3);j++){ if(board[i][j].number==value){ cout<<"That value is in conflict in this subgrid\n"; moveError=false; } } } return true; }

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