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• Difference in behaviour (GCC and Visual C++)

  - by Prasoon Saurav

  Consider the following code. #include <stdio.h> #include <vector> #include <iostream> struct XYZ { int X,Y,Z; }; std::vector<XYZ> A; int rec(int idx) { int i = A.size(); A.push_back(XYZ()); if (idx >= 5) return i; A[i].X = rec(idx+1); return i; } int main(){ A.clear(); rec(0); puts("FINISH!"); } I couldn't figure out the reason why the code gives a segmentation fault on Linux (IDE used: Code::Blocks) whereas on Windows (IDE used: Visual C++) it doesn't. When I used Valgrind just to check what actually the problem was, I got this output. I got Invalid write of size 4 at four different places. Then why didn't the code crash when I used Visual C++? Am I missing something?

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• C++ data member initializer is not allowed

  - by user1435915

  I totally new to C++ so bear with me. I want to make a class with a static array, and access to this array from the main. Here is what i want to do in C#. namespace ConsoleApplication1 { class Program { static void Main(string[] args) { Class a = new Class(); Console.WriteLine(a.arr[1]); } } } ===================== namespace ConsoleApplication1 { class Class { public static string[] s_strHands = new string[]{"one","two","three"}; } } Here is what i have tried: // justfoolin.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include <string> #include <iostream> using namespace std; class Class { public: static string arr[3] = {"one", "two", "three"}; }; int _tmain(int argc, _TCHAR* argv[]) { Class x; cout << x.arr[2] << endl; return 0; } But i got: IntelliSense: data member initializer is not allowed

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• Copy constructor called even when returning by reference?

  - by Johnyy

  Hi, I am testing the return of local objects by reference. My original test went well but something else happens unexpected. #include <iostream> using namespace std; class MyInt { public: MyInt(int i){ value = new int(i); } ~MyInt(){ delete value; } int getValue(){ return *value; } MyInt(const MyInt &b){ cout<<"Copy"<<endl; } private: int* value; }; MyInt& returnref(){ MyInt a(10); cout<<"Returning from returnref()"<<endl; return a; } int main(){ MyInt a = returnref(); cout<<a.getValue()<<endl; return 0; } My console prints "Returning from ..." then "Copy" then a random value. My understanding of pass by reference is that it does not need to make any copy. Why is it not doing what I expected?

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• Hello world/Console Project in Visual Studio 2008 64 bit

  - by grobartn

  So I am trying to run console 64 bit Hello World program. I have Windows 7 Enterprise x64 bit version. I have installed Visual Studio 2008 and have added all of components needed for 64 bit. I want to create simple console application. It turns out to be a problem. I have simple standard hello world project. I have created it using New Project - Empty project. I added main.cpp that contains this: #include <iostream> using namespace std; int main() { cout << "howdy\n"; } I added new configuration to the project by clicking on Config Manager and added x64 config. Compiled and it compiles. Tried running it and cmd.exe shoots up with following error: "The application has failed to start because its side-by-side configuration is in correct. Please see the application event log or use the command-line sxstrace.e xe tool for more detail. Press any key to continue . . . " Which set-up step if any I am missing. What am I doing wrong and how should I go about setting simple console hello world in 64 bit world. Thanks for any help

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• binary_search not working for a vector<string>

  - by VaioIsBorn

  #include <iostream> #include <string> #include <vector> #include <algorithm> using namespace std; int main(void) { string temp; vector<string> encrypt, decrypt; int i,n, co=0; cin >> n; for(i=0;i<n;i++) { cin >> temp; encrypt.push_back(temp); } for(i=0;i<n;i++) { cin >> temp; decrypt.push_back(temp); } for(i=0;i<n;i++) { temp = encrypt[i]; if((binary_search(decrypt.begin(), decrypt.end(), temp)) == true) ++co; } cout << co << endl; return 0; } It reads two equal lists of strings and should print out how many of the words in the first list are also found in the second list, simple. Not giving me the expexted results and i think the problem is in binary_search. Can you tell me why ?

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• gcc -finline-functions behaviour?

  - by user176168

  I'm using gcc with the -finline-functions optimization for release builds. In order to combat code bloat because I work on an embedded system I want to say don't inline particular functions. The obvious way to do this would be through function attributes ie attribute(noinline). The problem is this doesn't seem to work when I switch on the global -finline-functions optimisation which is part of the -O3 switch. It also has something to do with it being templated as a non templated version of the same function doesn't get inlined which is as expected. Has anybody any idea of how to control inlining when this global switch is on? Here's the code: #include <cstdlib> #include <iostream> using namespace std; class Base { public: template<typename _Type_> static _Type_ fooT( _Type_ x, _Type_ y ) __attribute__ (( noinline )); }; template<typename _Type_> _Type_ Base::fooT( _Type_ x, _Type_ y ) { asm(""); return x + y; } int main(int argc, char *argv[]) { int test = Base::fooT( 1, 2 ); printf( "test = %d\n", test ); system("PAUSE"); return EXIT_SUCCESS; }

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• Compilation problem in the standard x86_64 libraries

  - by user350282

  Hi everyone, I am having trouble compiling a program I have written. I have two different files with the same includes but only one generates the following error when compiled with g++ /usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib/crt1.o: In function `_start': /build/buildd/eglibc-2.10.1/csu/../sysdeps/x86_64/elf/start.S:109: undefined reference to `main' collect2: ld returned 1 exit status The files I am including in my header are as follows: #include <google/sparse_hash_map> using google::sparse_hash_map; #include <ext/hash_map> #include <math.h> #include <iostream> #include <queue> #include <vector> #include <stack> using std::priority_queue; using std::stack; using std::vector; using __gnu_cxx::hash_map; using __gnu_cxx::hash; using namespace std; Searching the internet for those two lines hasn't resulted in anything to help me. I would be very grateful for any advice. Thank you

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• STL vector performance

  - by iAdam

  STL vector class stores a copy of the object using copy constructor each time I call push_back. Wouldn't it slow down the program? I can have a custom linkedlist kind of class which deals with pointers to objects. Though it would not have some benefits of STL but still should be faster. See this code below: #include <vector> #include <iostream> #include <cstring> using namespace std; class myclass { public: char* text; myclass(const char* val) { text = new char[10]; strcpy(text, val); } myclass(const myclass& v) { cout << "copy\n"; //copy data } }; int main() { vector<myclass> list; myclass m1("first"); myclass m2("second"); cout << "adding first..."; list.push_back(m1); cout << "adding second..."; list.push_back(m2); cout << "returning..."; myclass& ret1 = list.at(0); cout << ret1.text << endl; return 0; } its output comes out as: adding first...copy adding second...copy copy The output shows the copy constructor is called both times when adding and when retrieving the value even then. Does it have any effect on performance esp when we have larger objects?

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• Template compilation error in Sun Studio 12

  - by Jagannath

  We are migrating to Sun Studio 12.1 and with the new compiler [ CC: Sun C++ 5.10 SunOS_sparc 2009/06/03 ]. I am getting compilation error while compiling a code that compiled fine with earlier version of Sun Compiler [ CC: Sun WorkShop 6 update 2 C++ 5.3 2001/05/15 ]. This is the compilation error I get. "Sample.cc": Error: Could not find a match for LoopThrough(int[2]) needed in main(). 1 Error(s) detected. * Error code 1. CODE: #include <iostream> #define PRINT_TRACE(STR) \ std::cout << __FILE__ << ":" << __LINE__ << ":" << STR << "\n"; template<size_t SZ> void LoopThrough(const int(&Item)[SZ]) { PRINT_TRACE("Specialized version"); for (size_t index = 0; index < SZ; ++index) { std::cout << Item[index] << "\n"; } } /* template<typename Type, size_t SZ> void LoopThrough(const Type(&Item)[SZ]) { PRINT_TRACE("Generic version"); } */ int main() { { int arr[] = { 1, 2 }; LoopThrough(arr); } } If I uncomment the code with Generic version, the code compiles fine and the generic version is called. I don't see this problem with MSVC 2010 with extensions disabled and the same case with ideone here. The specialized version of the function is called. Now the question is, is this a bug in Sun Compiler ? If yes, how could we file a bug report ?

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• Type casting in C++ by detecting the current 'this' object type

  - by Elroy

  My question is related to RTTI in C++ where I'm trying to check if an object belongs to the type hierarchy of another object. The BelongsTo() method checks this. I tried using typeid, but it throws an error and I'm not sure about any other way how I can find the target type to convert to at runtime. #include <iostream> #include <typeinfo> class X { public: // Checks if the input type belongs to the type heirarchy of input object type bool BelongsTo(X* p_a) { // I'm trying to check if the current (this) type belongs to the same type // hierarchy as the input type return dynamic_cast<typeid(*p_a)*>(this) != NULL; // error C2059: syntax error 'typeid' } }; class A : public X { }; class B : public A { }; class C : public A { }; int main() { X* a = new A(); X* b = new B(); X* c = new C(); bool test1 = b->BelongsTo(a); // should return true bool test2 = b->BelongsTo(c); // should return false bool test3 = c->BelongsTo(a); // should return true } Making the method virtual and letting derived classes do it seems like a bad idea as I have a lot of classes in the same type hierarchy. Or does anybody know of any other/better way to the do the same thing? Please suggest.

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• How to treat Base* pointer as Derived<T>* pointer?

  - by dehmann

  I would like to store pointers to a Base class in a vector, but then use them as function arguments where they act as a specific class, see here: #include <iostream> #include <vector> class Base {}; template<class T> class Derived : public Base {}; void Foo(Derived<int>* d) { std::cerr << "Processing int" << std::endl; } void Foo(Derived<double>* d) { std::cerr << "Processing double" << std::endl; } int main() { std::vector<Base*> vec; vec.push_back(new Derived<int>()); vec.push_back(new Derived<double>()); Foo(vec[0]); Foo(vec[1]); delete vec[0]; delete vec[1]; return 0; } This doesn't compile: error: call of overloaded 'Foo(Base*&)' is ambiguous Is it possible to make it work? I need to process the elements of the vector differently, according to their int, double, etc. types.

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• Boost Property_Tree iterators, how to handle them?

  - by Andry

  Hello... I am sorry but I asked a question about the same argument before, but my problem concerns another aspect of the one described in that question (How to iterate a boost...). My problem is this, take a look at the following code: #include <iostream> #include <string> #include <boost/property_tree/ptree.hpp> #include <boost/property_tree/xml_parser.hpp> #include <boost/algorithm/string/trim.hpp> int main(int argc, char** argv) { using boost::property_tree::ptree; ptree pt; read_xml("try.xml", pt); ptree::const_iterator end = pt.end(); for (ptree::const_iterator it = pt.begin(); it != end; it++) std::cout << "Here " << it->? << std::endl; } Well, as told me in the previous question, there is the possibility to use iterators on property_tree in Boost, but I do not know what type it is... and what methods or properties I can use... Well, I assume that it must be another ptree or something representing another xml hierarchy to be browsed again (if I want) but documentation about this is very bad... I do not know why, but in boost docs I cannot find nothing good about this... just something about a macro to browse nodes, but this approach is one I would really like to avoid... Well, the question is so... Once getting the iterator on a ptree, how can I access node name, value, parameters (a node in a xml file)? Thankyou

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• invalid scalar hex value 0x8000000 and over

  - by kioto

  Hi. I found a problem getting hex value from yaml file. It couldn't get hex value 0x80000000 and over. Following is a sample C++ program. // ymlparser.cpp #include <iostream> #include <fstream> #include "yaml-cpp/yaml.h" int main(void) { try { std::ifstream fin("hex.yaml"); YAML::Parser parser(fin); YAML::Node doc; parser.GetNextDocument(doc); int num1; doc["hex1"] >> num1; printf("num1 = 0x%x\n", num1); int num2; doc["hex2"] >> num2; printf("num2 = 0x%x\n", num2); return 0; } catch(YAML::ParserException& e) { std::cout << e.what() << "\n"; } } hex.yaml hex1: 0x7FFFFFFF hex2: 0x80000000 Error message is here. $ ./ymlparser num1 = 0x7fffffff terminate called after throwing an instance of 'YAML::InvalidScalar' what(): yaml-cpp: error at line 2, column 7: invalid scalar Aborted Environment yaml-cpp : getting from svn, March.22.2010 or v0.2.5 OS : Ubuntu 9.10 i386 I need to get hex the value on yaml-cpp now, but I have no idea. Please tell me how to get it another way. Thanks,

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• Path String Combination Question.

  - by Nano HE

  Hi. Please see my code below. ifstream myLibFile ("libs//%s" , line); // Compile failed here ??? I want to combine the path string and open the related file again. #include <iostream> #include <fstream> #include <string> using namespace std; int main () { string line; ifstream myfile ("libs//Config.txt"); // There are several file names listed in the COnfig.txt file line by line. if (myfile.is_open()) { while (! myfile.eof() ) { getline (myfile,line); cout << line << endl; // Read details lib files based on the each line file name. string libFileLine; ifstream myLibFile ("libs//%s" , line); // Compile failed here ??? if (myLibFile.is_open()) { while (! myLibFile.eof() ) { print "success"; } myLibFile.close(); } } myfile.close(); } else cout << "Unable to open file"; return 0; }

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• Specifying character

  - by danutenshu

  So below I have a code in C++ that is supposed to invert the arguments in a vector, but not the sequence. I have listed my problems as sidenotes in the code below. The invert function is supposed to invert each argument, and then the main function just outputs the inverted words in same order For instance, program("one two three four")=ruof eerth owt eno #include <iostream> #include <string> using namespace std; int invert(string normal) { string inverted; for (int num=normal.size()-1; num>=0; num--) { inverted.append(normal[num]); //I don't know how to get each character //I need another command for append } return **inverted**; <---- } int main(int argc, char* argv[]) { string text; for (int a=1; a<argc; a++) { text.append(invert(argv[a])); //Can't run the invert function text.append(" "); } cout << text << endl; return 0; }

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• What happens to class members when malloc is used instead of new?

  - by Felix

  I'm studying for a final exam and I stumbled upon a curious question that was part of the exam our teacher gave last year to some poor souls. The question goes something like this: Is the following program correct, or not? If it is, write down what the program outputs. If it's not, write down why. The program: #include<iostream.h> class cls { int x; public: cls() { x=23; } int get_x(){ return x; } }; int main() { cls *p1, *p2; p1=new cls; p2=(cls*)malloc(sizeof(cls)); int x=p1->get_x()+p2->get_x(); cout<<x; return 0; } My first instinct was to answer with "the program is not correct, as new should be used instead of malloc". However, after compiling the program and seeing it output 23 I realize that that answer might not be correct. The problem is that I was expecting p2->get_x() to return some arbitrary number (whatever happened to be in that spot of the memory when malloc was called). However, it returned 0. I'm not sure whether this is a coincidence or if class members are initialized with 0 when it is malloc-ed. Is this behavior (p2->x being 0 after malloc) the default? Should I have expected this? What would your answer to my teacher's question be? (besides forgetting to #include <stdlib.h> for malloc :P)

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• How to refresh/redraw the screen (not the program window)

  - by mohrphium

  I'm having a bit of a hard time figuring out, how to remove a drawn ellipse after it has been drawn somewhere else. I need a circle to follow my mouse all the time and this is all the program should do. I get the mousepositions and draw my circle but how can I remove the last one? #include <Windows.h> #include <iostream> void drawRect(int a1, int a2){ HDC screenDC = ::GetDC(0); //Draw circle at mouse position ::Ellipse(screenDC, a1, a2+5, a1+9, a2+14); ::ReleaseDC(0, screenDC); //::InvalidateRect(0, NULL, TRUE); //<- I tried that but then everything flickers //Also, the refresh rate is not fast enough... still some circles left } int main(void) { int a1; int a2; bool exit=false; while (exit!=true) { POINT cursorPos; GetCursorPos(&cursorPos); float x = 0; x = cursorPos.x; float y = 0; y = cursorPos.y; a1=(int)cursorPos.x; a2=(int)cursorPos.y; drawRect(a1, a2); } } I am working with graphics and all that stuff for the first time. Im kinda stuck here... once again. Thanks.

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• An error saying unidentifed function "push", "pop", and"display" occurs, what should i add to fix i

  - by Alesha Aris

  #include<stdio.h> #include<iostream.h> #include<conio.h> #include<stdlib.h>(TOP) #include<fstream.h> #define MAX 5 int top = -1; int stack_arr[MAX]; main() { int choice; while(1) { printf("1.Push\n"); printf("2.Pop\n"); printf("3.Display\n"); printf("4.Quit\n"); printf("Enter your choice : "); scanf("%d",&choice); switch(choice) { case 1 : push(); break; case 2: pop(); break; case 3: display(); break; case 4: exit(1); default: printf("Wrong choice\n"); }/*End of switch*/ }/*End of while*/ }/*End of main()*/ push() { int pushed_item; if(top == (MAX-1)) printf("Stack Overflow\n"); else { printf("Enter the item to be pushed in stack : "); scanf("%d",&pushed_item); top=top+1; stack_arr[top] = pushed_item; } }/*End of push()*/ pop() { if(top == -1) printf("Stack Underflow\n"); else { printf("Popped element is : %d\n",stack_arr[top]); top=top-1; } }/*End of pop()*/ display() { int i; if(top == -1) printf("Stack is empty\n"); else { printf("Stack elements :\n"); for(i = top; i >=0; i--) printf("%d\n", stack_arr[i] ); } }/*End of display()*/

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• Retrieve the Value of An Integer Variable

  - by Abluescarab

  This is probably easily figured out (I feel very stupid right now), but I can't find a solution anywhere, for some reason. Perhaps I'm not searching for the right thing. And maybe it's in some beginner tutorial I haven't watched. Anyway, I was wondering how to retrieve the value of an integer variable in C++? I know you can use cin.getline() for string variables, but I received an error message when I attempted that with an integer variable (and rightfully so, I know it was wrong, but I was looking for a solution). My project is a Win32 console application. What I'm trying to do is ask a user to input a number, stored in the variable n. Then I take the value of n and perform various math functions with it. In my header file, I have string, windows, iostream, stdio, math, and fstream. Do I need to add another library? There's not much more to tell. I can post my code if I must. EDIT: cout << "TEST SINE"; cout << "\nPlease enter a number.\n\n"; cin >> n; break; Here's the code I'm trying to use. Is this all I need to do? If so, how do I incorporate the variable so I can test it using sin, cos, and tan? Yet again, thanks ahead of time.

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• How to define and use a friend function to a temlate class with the same template?

  - by Narek

  I have written the following code: #include <iostream> using namespace std; template <class T> class AA { T a; public: AA() { a = 7; } friend void print(const AA<T> & z); }; template <class T> void print(const AA<T> & z) { cout<<"Print: "<<z.a<<endl; } void main() { AA<int> a; print<int>(a); } And getting the following error: error C2248: 'AA<T>::a' : cannot access private member declared in class 'AA<T>' 1> with 1> [ 1> T=int 1> ] 1> c:\users\narek\documents\visual studio 2008\projects\aaa\aaa\a.cpp(7) : see declaration of 'AA<T>::a' 1> with 1> [ 1> T=int 1> ] 1> c:\users\narek\documents\visual studio 2008\projects\aaa\aaa\a.cpp(30) : see reference to function template instantiation 'void print<int>(const AA<T> &)' being compiled 1> with 1> [ 1> T=int 1> ] What's wrong?

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• Why does double dispatch not work in C++?

  - by Bruce

  #include<iostream.h> #include<conio.h> using namespace std; class SpaceShip {}; class GiantSpaceShip : public SpaceShip {}; class Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "Asteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "Asteroid hit a GiantSpaceShip" << endl; } }; class ExplodingAsteroid : public Asteroid { public: virtual void CollideWith(SpaceShip *) { cout << "ExplodingAsteroid hit a SpaceShip" << endl; } virtual void CollideWith(GiantSpaceShip *) { cout << "ExplodingAsteroid hit a GiantSpaceShip" << endl; } }; int main() { SpaceShip * s = new GiantSpaceShip(); Asteroid * a = new ExplodingAsteroid(); a->CollideWith(s); getch(); return 0; } How can I enable double dispatch in C++?

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• UnauthorizedAccessException when running desktop application from shared folder

  - by Atara

  I created a desktop application using VS 2008. When I run it locally, all works well. I shared my output folder (WITHOUT allowing network users to change my files) and ran my exe from another Vista computer on our intranet. When running the shared exe, I receive "System.UnauthorizedAccessException" when trying to read a file. How can I give permission to allow reading the file? Should I change the code? Should I grant permission to the application\folder on the Vista computer? how? Notes: I do not use ClickOnce. the application should be distributed using xcopy. My application target framework is ".Net Framework 2.0" On the Vista computer, "controlPanel | UninstallOrChangePrograms" it says it has "Microsoft .Net Framework 3.5 SP1" I also tried to map the folder drive, but got the same errors, only now the fileName is "T:\my.ocx" ' ---------------------------------------------------------------------- ' my code: Dim src As String = mcGlobals.cmcFiles.mcGetFileNameOcx() Dim ioStream As New System.IO.FileStream(src, IO.FileMode.Open) ' ---------------------------------------------------------------------- Public Shared Function mcGetFileNameOcx() As String ' ---------------------------------------------------------------------- Dim dirName As String = Application.StartupPath & "\" Dim sFiles() As String = System.IO.Directory.GetFiles(dirName, "*.ocx") Dim i As Integer For i = 0 To UBound(sFiles) Debug.WriteLine(System.IO.Path.GetFullPath(sFiles(i))) ' if found any - return the first: Return System.IO.Path.GetFullPath(sFiles(i)) Next Return "" End Function ' ---------------------------------------------------------------------- ' The Exception I receive: System.UnauthorizedAccessException: Access to the path '\\computerName\sharedFolderName\my.ocx' is denied. at System.IO._Error(Int32 errorCode, String maybeFullPath) at System.IO.FileStream.Init(...) at System.IO.FileStream..ctor(...) at System.IO.FileStream..ctor(String path, FileMode mode) ' ----------------------------------------------------------------------

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• C++ MACRO that will execute a block of code and a certain command after that block.

  - by Poni

  void main() { int xyz = 123; // original value { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends int original_value = xyz; // should be 123 } void main() { int xyz = 123; // original value MACRO_NAME(xyz = 123) // the macro takes the code code that should be executed at the end of the block. { // code block starts xyz++; if(xyz < 1000) xyz = 1; } // code block ends << how to make the macro execute the "xyz = 123" statement? int original_value = xyz; // should be 123 } Only the first main() works. I think the comments explain the issue. It doesn't need to be a macro but to me it just sounds like a classical "macro-needed" case. By the way, there's the BOOST_FOREACH macro/library and I think it does the exact same thing I'm trying to achieve but it's too complex for me to find the essence of what I need. From its introductory manual page, an example: #include <string> #include <iostream> #include <boost/foreach.hpp> int main() { std::string hello( "Hello, world!" ); BOOST_FOREACH( char ch, hello ) { std::cout << ch; } return 0; }

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• Unresolved external symbol error in c++

  - by Crystal

  I am trying to do a simple hw problem involving namespace, static data members and functions. I am getting an unresolved external symbol error Error 1 error LNK2001: unresolved external symbol "private: static double JWong::SavingsAccount::annualInterestRate" (?annualInterestRate@SavingsAccount@JWong@@0NA) SavingsAccount.obj SavingsAccount And I don't see why I am getting this error. Maybe I don't know something about static variables compared to regular data members that is causing this error. Here is my code: SavingsAccount.h file #ifndef JWONG_SAVINGSACCOUNT_H #define JWONG_SAVINGSACCOUNT_H namespace JWong { class SavingsAccount { public: // default constructor SavingsAccount(); // constructor SavingsAccount(double savingsBalance); double getSavingsBalance(); void setSavingsBalance(double savingsBalance); double calculateMonthlyInterest(); // static functions static void modifyInterestRate(double newInterestRate); static double getAnnualInterestRest(); private: double savingsBalance; // static members static double annualInterestRate; }; } #endif SavingsAccount.cpp file #include <iostream> #include "SavingsAccount.h" // default constructor, set savingsBalance to 0 JWong::SavingsAccount::SavingsAccount() : savingsBalance(0) {} // constructor JWong::SavingsAccount::SavingsAccount(double savingsBalance) : savingsBalance(savingsBalance) {} double JWong::SavingsAccount::getSavingsBalance() { return savingsBalance; } void JWong::SavingsAccount::setSavingsBalance(double savingsBalance) { this->savingsBalance = savingsBalance; } // returns monthly interest and sets savingsBalance to new amount double JWong::SavingsAccount::calculateMonthlyInterest() { double monthlyInterest = savingsBalance * SavingsAccount::annualInterestRate / 12; setSavingsBalance(savingsBalance + monthlyInterest); return monthlyInterest; } void JWong::SavingsAccount::modifyInterestRate(double newInterestRate) { SavingsAccount::annualInterestRate = newInterestRate; } double JWong::SavingsAccount::getAnnualInterestRest() { return SavingsAccount::annualInterestRate; }

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• Function pointers to member functions

  - by Jacob

  There are several duplicates of this but nobody explains why I can use a member variable to store the pointer (in FOO) but when I try it with a local variable (in the commented portion of BAR), it's illegal. Could anybody explain this? #include <iostream> using namespace std; class FOO { public: int (FOO::*fptr)(int a, int b); int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { fptr = &FOO::add_stuff; cout<<(this->*fptr)(a,b)<<endl; } }; class BAR { public: int add_stuff(int a, int b) { return a+b; } void call_adder(int a, int b) { //int (BAR::*fptr)(int a, int b); //fptr = &BAR::add_stuff; //cout<<(*fptr)(a,b)<<endl; } }; int main() { FOO test; test.call_adder(10,20); return 0; }

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