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• Is incrementing in a loop exponential time?

  - by user356106

  I've a simple but confusing doubt about whether the program below runs in exponential time. The question is : given a +ve integer as input, print it out. The catch is that you deliberately do this in a loop, like this: int input,output=0; cininput; while(input--) ++output; // Takes time proportional to the value of input cout<< output; I'm claiming that this problem runs in exponential time. Because, the moment you increase the # of bits in input by 1, the program takes double the amount of time to execute. Put another way, to print out log2(input) bits, it takes O(input) time. Is this reasoning right?

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• Avoid warning 'Unreferenced Formal Parameter'

  - by bdhar

  I have a super class like this: class Parent { public: virtual void Function(int param); }; void Parent::Function(int param) { std::cout << param << std::endl; } ..and a sub-class like this: class Child : public Parent { public: void Function(int param); }; void Child::Function(int param) { ;//Do nothing } When I compile the sub-class .cpp file, I get this error warning C4100: 'param' : unreferenced formal parameter As a practise, we used to treat warnings as errors. How to avoid the above warning? Thanks.

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• How I can print the wchar_t values to console?

  - by zed91

  Example: #include <iostream> using namespace std; int main() { wchar_t en[] = L"Hello"; wchar_t ru[] = L"??????"; //Russian language cout << ru << endl << en; return 0; } This code only prints HEX-values like adress. How to print the wchar_t string?

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• Pure virtual destructor in interface

  - by ALOR

  Hello all. Here is my problem. I'm making C++ dll, which extensively relies on instance object exports. So i return my actual instances as a pointers to interface through some exported factory method. Interfaces i use are purely virtual, to avoid linking problame. So i need a pure virtual destructor too, and i implemented one (with empty body, as i googled it). All compiles perfectly well, except... I can't see, if the actual destructors are called or not - because when i added some std::cout << "hello destructor"; i never get to see it. I have some explicit "delete obj", that's not the problem. Am i missing something? Is there another way to delete my object through interface?

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• How to get Drive Letter Using WMI

  - by new

  i get the vid and pid of the usb devices plugged into my system using WMI. Now i want to get the drive letter corresponding to the device vid and pid i retrievd. code hres = pSvc->ExecQuery( bstr_t("WQL"), bstr_t("SELECT * FROM Win32_USBControllerDevice"), WBEM_FLAG_FORWARD_ONLY | WBEM_FLAG_RETURN_IMMEDIATELY, NULL, &pEnumerator); if (FAILED(pclsObj->Get(L"Dependent", 0, &vtProp, 0, 0))) { cout<<"The specified property is not found."<<endl; } else { wcout <<vtProp.bstrVal << endl; } i get like below \NJ96\root\cimv2:Win32_PnPEntity.DeviceID="USB\VID_1A8D&PID_1000\35809402 0874450" how can i map DRIVE LETTER to my above output using the WMI please help me out

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• How to free memory in try-catch blocks?

  - by Kra

  Hi, I have a simple question hopefully - how does one free memory which was allocated in the try block when the exception occurs? Consider the following code: try { char *heap = new char [50]; //let exception occur here delete[] heap; } catch (...) { cout << "Error, leaving function now"; //delete[] heap; doesn't work of course, heap is unknown to compiler return 1; } How can I free memory after the heap was allocated and exception occurred before calling delete[] heap? Is there a rule not to allocate memory on heap in these try .. catch blocks? Thanks

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• functor returning 0

  - by Jon

  I've recently started teaching myself the standard template library. I was curious as to why the GetTotal() method in this class is returning 0? ... class Count { public: Count() : total(0){} void operator() (int val){ total += val;} int GetTotal() { return total;} private: int total; }; void main() { set<int> s; Count c; for(int i = 0; i < 10; i++) s.inset(i); for_each(s.begin(), s.end(), c); cout << c.GetTotal() << endl; }

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• Why is my implementation of strcmp not returning the proper value?

  - by Avanish Giri

  Why is this printing out 0 back in main but 6 when it is inside of the strcmp function? 7 int main() 8 { 9 char* str = "test string"; 10 char* str2 = "test strong"; 11 //printf("string length = %d\n",strlen(str)); 12 13 int num = strcmp(str,str2); 14 15 printf("num = %d\n",num); 16 } 29 int strcmp(char* str, char* str2) 30 { 31 if(*str == '\0' && *str2 == '\0') 32 return 0; 33 if(*str2 - *str == 0) 34 { 35 strcmp(str+1,str2+1); 36 } 37 else 38 { 39 int num = *str2 - *str; 40 cout << "num = " <<num<<endl; 41 return num; 42 } 43 } The output is: num = 6 num = 0 Why is it printing 0 when obviously the value that it should be returning is 6?

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• Why do I get a "warning: no newline at end of file" ?

  - by user198729

  The file is a helloworld.cpp: #include <iostream> using namespace std; int main() { if(true) cout << "!!!Hello World!!!" << endl; // prints !!!Hello World!!! return 0; } But when I build it,get a warning: g++ -Wall -O2 -c -o hw.o hw.cpp hw.cpp:8:2: warning: no newline at end of file g++ -o myprog hw.o If I add a newline at the end,the warning will go. Why is that newline at end of file recommended in a cpp source file?

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• Returning a local object from a function

  - by pocoa

  Is this the right way to return an object from a function? Car getCar(string model, int year) { Car c(model, year); return c; } void displayCar(Car &car) { cout << car.getModel() << ", " << car.getYear() << endl; } displayCar(getCar("Honda", 1999)); I'm getting an error, "taking address of temporary". Should I use this way: Car &getCar(string model, int year) { Car c(model, year); return c; }

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• Why won't this compile and how can it be implemented so that it does?

  - by George Edison

  Here is some C++ code I'm playing around with: #include <iostream> #include <vector> #define IN , #define FOREACH(x,y) for(unsigned int i=0;i<y.size();i++) { x=y[i]; #define ENDFOREACH } using namespace std; int main() { vector<int> ints; ints.push_back(3); ints.push_back(4); ints.push_back(5); ints.push_back(6); FOREACH(int item IN ints) cout << item; ENDFOREACH return 0; } However, I get an error: macro "FOREACH" requires 2 arguments, but only 1 given The code compiles if I change the IN to a comma. How can I get the IN to take the place of a comma?

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• Can I use vector as index in map structure in c++?

  - by tsubasa

  I attempted to do something like this but it does not compile: class point { public: int x; int y; }; int main() { vector<point> vp1; vector<point> vp2; vector<point> vp3; map < vector<point>, int > m; m[vp1] = 1; m[vp2] = 2; m[vp3] = 3; map < vector<point>, int >::iterator it; for (it=m.begin(); it!=m.end(); it++) { cout<<m[it->first]<<endl; } return 0; }

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• pass by pointer is not working

  - by user323422

  #include"iostream" class CMessage { public:int a; CMessage(){} ~CMessage(){} }; void Testing(CMessage *f_pMessage)//l_pMessage is output parameter { f_pMessage = new CMessage(); f_pMessage->a = 1; } int main() { CMessage *l_pMessage =NULL; Testing(l_pMessage); std::cout<<l_pMessage->a;//getting l_pMessage = NULL; return 0; } when i called testing then inside testing f_pMessage is getting intialize but as ssoon as i after excuting testing function it should be store in l_Pmessage but it is showing NULL.confussed.....

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• How do I output the preorder traversal of a tree given the inorder and postorder tranversal?

  - by user342580

  Given the code for outputing the postorder traversal of a tree when I have the preorder and the inorder traversal in an interger array. How do I similarily get the preorder with the inorder and postorder array given? void postorder( int preorder[], int prestart, int inorder[], int inostart, int length) { if(length==0) return; //terminating condition int i; for(i=inostart; i<inostart+length; i++) if(preorder[prestart]==inorder[i])//break when found root in inorder array break; postorder(preorder, prestart+1, inorder, inostart, i-inostart); postorder(preorder, prestart+i-inostart+1, inorder, i+1, length-i+inostart-1); cout<<preorder[prestart]<<" "; } Here is the prototype for preorder() void preorder( int inorderorder[], int inostart, int postorder[], int poststart, int length)

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• How to write Cyrillic text in C++ console?

  - by VextoR

  For example, if I write: cout << "??????!" << endl; //it's hello in Russian in console it would be something like "-?????!" ok, I know that we can use: setlocale(LC_ALL, "Russian"); but after that not working command line arguments in russian (if I start my program through BAT file): StartProgram.bat chcp 1251 MyProgram.exe -user=???? -password=?????? so, after setlocale program can't read russian arguments properly. This happens because BAT file in CP1251, but console is in CP866 So, there is a question: How to write in C++ console russian text and same time russian command line arguments have to be read properly thanks

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• In C++, what is the "order of precedence" for shadowed variable names?

  - by Emile Cormier

  In C++, what is the "order of precedence" for shadowed variable names? I can't seem to find a concise answer online. For example: #include <iostream> int shadowed = 1; struct Foo { Foo() : shadowed(2) {} void bar(int shadowed = 3) { std::cout << shadowed << std::endl; // What does this output? } int shadowed; }; int main() { Foo().bar(); } I can't think of any other scopes where a variable might conflict. Please let me know if I missed one.

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• Reading in 4 bytes at a time

  - by alphomega

  I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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• C++: can't static_cast from double* to int*

  - by samoz

  When I try to use a static_cast to cast a double* to an int*, I get the following error: invalid static_cast from type ‘double*’ to type ‘int*’ Here is the code: #include <iostream> int main() { double* p = new double(2); int* r; r=static_cast<int*>(p); std::cout << *r << std::endl; } I understand that there would be problems converting between a double and an int, but why is there a problem converting between a double* and an int*?

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• Difference between debug and release.

  - by atch

  Why when I'm debugging in debug mode everything in code below works as suppose to but when I switch to release I'm getting strange result? void say_hello(int argc, char* argv[])//In release mode argc has different values from 124353625 to 36369852 <include iostream> { std::cout << "In say_hello()\n"; } int main(int argc, char* argv[]) { say_hello(3,argv);//when instead of literal I enter "argc" everything is ok. return 0; } Thanks for help.

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• What's wrong with the following code ?

  - by dada

  #include <iostream> #include <string> using namespace std; int main(void) { string a; cin>>a; a.erase(a.end()-1); a.erase(a.begin()+1); string ge = "oae"; a.insert(a.begin()+1, ge); cout<<a<<endl; return 0; } It doesn't compile and i don't know why. Can you tell me what's wrong

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• Pass temporary object to function that takes pointer

  - by Happy Mittal

  I tried following code : #include<iostream> #include<string> using namespace std; string f1(string s) { return s="f1 called"; } void f2(string *s) { cout<<*s<<endl; } int main() { string str; f2(&f1(str)); } But this code doesn't compile. What I think is : f1 returns by value so it creates temporary, of which I am taking address and passing to f2. Now Please explain me where I am thinking wrong?

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• How to declare a variable that spans multiple lines

  - by Chris Wilson

  I'm attempting to initialise a string variable in C++, and the value is so long that it's going to exceed the 80 character per line limit I'm working to, so I'd like to split it to the next line, but I'm not sure how to do that. I know that when splitting the contents of a stream across multiple lines, the syntax goes like cout << "This is a string" << "This is another string"; Is there an equivalent for variable assignment, or do I have to declare multiple variables and concatenate them? Edit: I misspoke when I wrote the initial question. When I say 'next line', I'm just meaning the next line of the script. When it is printed upon execution, I would like it to be on the same line.

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• Why is this c++ string concatenation missing a space?

  - by danutenshu

  I am working with c++ strings, and am a beginner at programming. I am expecting: 99 Red Balloons But I am receiving: 99 RedBalloons Why is that? #include <string> #include <iostream> using namespace std; int main() { string text = "9"; string term( "9 "); string info = "Toys"; string color; char hue[4] = {'R','e','d','\0'}; color = hue; info = "Balloons"; text += (term + color + info); cout << endl << text << endl; return 0; }

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• C++ Detecting ENTER key pressed by user

  - by user69514

  I have a loop where I ask the user to enter a name. I need to stop when the user presses the ENTER key..... or when 20 names have been entered. However my method doesn't stop when the user presses the ENTER key //loop until ENTER key is entered or 20 elements have been added bool stop = false; int ind = 0; while( !stop || ind >= 20 ){ cout << "Enter name #" << (ind+1) << ":"; string temp; getline(cin, temp); int enterKey = atoi(temp.c_str()); if(enterKey == '\n'){ stop = true; } else{ names[ind] = temp; } ind++; }

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• Constructor Type Coercion in C++

  - by Robert Mason

  Take the following class: class mytype { double num; public: mytype(int a) { num = sqrt(a); } void print() { cout << num; } } Say there is a method which takes a mytype: void foo(mytype a) { a.print(); } Is it legal c++ (or is there a way to implement this) to call foo(4), which would (in theory) output 2? From what I can glean you can overload type casts from a user defined class, but not to. Can constructor do this in a standards-compliant manner (assuming, of course, the constructor is not explicit). Hopefully there is a way to in the end have this legal: int a; cin >> a; foo(a); Note: this is quite obviously not the actual issue, but just an example for posting purposes. I can't just overload the function because of inheritance and other program-specific issues.

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