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  • string parsing to double fails in C++

    - by helixed
    Here's a fun one I've been trying to figure out. I have the following program: #include <iostream> #include <string> #include <sstream> using namespace std; int main(int argc, char *argv[]) { string s("5"); istringstream stream(s); double theValue; stream >> theValue; cout << theValue << endl; cout << stream.fail(); } The output is: 0 1 I don't understand why this is failing. Could somebody please tell me what I'm doing wrong? Thanks, helixed

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  • Is this good code? Linked List Stack Implementation

    - by Quik Tester
    I have used the following code for a stack implementation. The top keeps track of the topmost node of the stack. Now since top is a data member of the node function, each node created will have a top member, which ideally we wouldn't want. Firstly, is this good approach to coding? Secondly, will making top as static make it a better coding practice? Or should I have a global declaration of top? #include<iostream> using namespace std; class node { int data; node *top; node *link; public: node() { top=NULL; link=NULL; } void push(int x) { node *n=new node; n->data=x; n->link=top; top=n; cout<<"Pushed "<<n->data<<endl; } void pop() { node *n=new node; n=top; top=top->link; n->link=NULL; cout<<"Popped "<<n->data<<endl; delete n; } void print() { node *n=new node; n=top; while(n!=NULL) { cout<<n->data<<endl; n=n->link; } delete n; } }; int main() { node stack; stack.push(5); stack.push(7); stack.push(9); stack.pop(); stack.print(); } Any other suggestions welcome. I have also seen codes where there are two classes, where the second one has the top member. What about this? Thanks. :)

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  • C++ streams operator << and manipulators / formatters

    - by Ayman
    First, most of my recent work was Java. So even though I "know" C++, I do not want to write Java in C++. And C++ templates are one thing I will really miss when going back to Java. Now that this out of the way, if I want to do create a new stream formatter, say pic, that will have a single std::string parameter in it's constructor. I would like the user to be able to write something like: cout << pic("Date is 20../../..") << "100317" << endl; The output should be Date is 2010/03/17 How do I write the pic class? when the compiler sees the cout what are the underlying steps the compiler does?

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  • Setting minimum number of decimal places for std::ostream precision

    - by Phil Boltt
    Hi, Is there a way to set the "minimum" number of decimal places that a std::ostream will output? For example, say I have two doubles that I want to print: double a = 0; double b = 0.123456789; I can set my maximum decimal precision so that I output b exactly std::cout << std::setprecision(9) << b << std::endl; Is there a way to set "minimum" precision so that std::cout << a << std::endl; yields "0.0", not just "0"? Thanks! Phil

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  • Signals and threads - good or bad design decision?

    - by Jens
    I have to write a program that performs highly computationally intensive calculations. The program might run for several days. The calculation can be separated easily in different threads without the need of shared data. I want a GUI or a web service that informs me of the current status. My current design uses BOOST::signals2 and BOOST::thread. It compiles and so far works as expected. If a thread finished one iteration and new data is available it calls a signal which is connected to a slot in the GUI class. My question(s): Is this combination of signals and threads a wise idea? I another forum somebody advised someone else not to "go down this road". Are there potential deadly pitfalls nearby that I failed to see? Is my expectation realistic that it will be "easy" to use my GUI class to provide a web interface or a QT, a VTK or a whatever window? Is there a more clever alternative (like other boost libs) that I overlooked? following code compiles with g++ -Wall -o main -lboost_thread-mt <filename>.cpp code follows: #include <boost/signals2.hpp> #include <boost/thread.hpp> #include <boost/bind.hpp> #include <iostream> #include <iterator> #include <string> using std::cout; using std::cerr; using std::string; /** * Called when a CalcThread finished a new bunch of data. */ boost::signals2::signal<void(string)> signal_new_data; /** * The whole data will be stored here. */ class DataCollector { typedef boost::mutex::scoped_lock scoped_lock; boost::mutex mutex; public: /** * Called by CalcThreads call the to store their data. */ void push(const string &s, const string &caller_name) { scoped_lock lock(mutex); _data.push_back(s); signal_new_data(caller_name); } /** * Output everything collected so far to std::out. */ void out() { typedef std::vector<string>::const_iterator iter; for (iter i = _data.begin(); i != _data.end(); ++i) cout << " " << *i << "\n"; } private: std::vector<string> _data; }; /** * Several of those can calculate stuff. * No data sharing needed. */ struct CalcThread { CalcThread(string name, DataCollector &datcol) : _name(name), _datcol(datcol) { } /** * Expensive algorithms will be implemented here. * @param num_results how many data sets are to be calculated by this thread. */ void operator()(int num_results) { for (int i = 1; i <= num_results; ++i) { std::stringstream s; s << "["; if (i == num_results) s << "LAST "; s << "DATA " << i << " from thread " << _name << "]"; _datcol.push(s.str(), _name); } } private: string _name; DataCollector &_datcol; }; /** * Maybe some VTK or QT or both will be used someday. */ class GuiClass { public: GuiClass(DataCollector &datcol) : _datcol(datcol) { } /** * If the GUI wants to present or at least count the data collected so far. * @param caller_name is the name of the thread whose data is new. */ void slot_data_changed(string caller_name) const { cout << "GuiClass knows: new data from " << caller_name << std::endl; } private: DataCollector & _datcol; }; int main() { DataCollector datcol; GuiClass mc(datcol); signal_new_data.connect(boost::bind(&GuiClass::slot_data_changed, &mc, _1)); CalcThread r1("A", datcol), r2("B", datcol), r3("C", datcol), r4("D", datcol), r5("E", datcol); boost::thread t1(r1, 3); boost::thread t2(r2, 1); boost::thread t3(r3, 2); boost::thread t4(r4, 2); boost::thread t5(r5, 3); t1.join(); t2.join(); t3.join(); t4.join(); t5.join(); datcol.out(); cout << "\nDone" << std::endl; return 0; }

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  • Why friend overloaded operator is preferred to conversion operator in this case

    - by skydoor
    Hi I have a code like this, I think both the friend overloaded operator and conversion operator have the similar function. However, why does the friend overloaded operator is called in this case? What's the rules? Thanks so much! class A{ double i; public: A(int i):i(i) {} operator double () const { cout<<"conversion operator"<<endl;return i;} // a conversion operator friend bool operator>(int i, A a); // a friend funcion of operator > }; bool operator>(int i, A a ){ cout<<"Friend"<<endl; return i>a.i; } int main() { A aa(1); if (0 > aa){ return 1; } }

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  • read file in C++

    - by Amm Sokun
    I am trying to read a list of words from a file in C++. However, the last word is read twice. I cannot understand why it is so. Can someone help me out? int main () { ifstream fin, finn; vector<string> vin; vector<string> typo; string word; fin.open("F:\\coursework\\pz\\gattaca\\breathanalyzer\\file.in"); if (!fin.is_open()) cout<<"Not open\n"; while (fin) { fin >> word; cout<<word<<endl; vin.push_back(word); } fin.close(); }

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  • How to add event listners / signals to a simple superman class?

    - by Kabumbus
    I can and would love to use boost or std for this. Sorry - I am new to C++. So I created a really simple program like: #include <iostream> #include <string> using namespace std; class superman { public: string punch(){return cout << "superman: I hit the bad guy!" << endl;}; }; int main() { superman clark; clark.punch(); cin.get(); } I want to add an event listner that would tell me when clark punched and cout something like "superman punched!". How to add such event listner and event function to my class?

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  • linker error in simple program: multiple definition of function

    - by BillyJean
    My function test is added to two different .cpp-files and the functions are private to their respective files as shown below test1.cpp #include <iostream> using namespace std; void test() { cout << "test" << endl; } test2.cpp #include <iostream> using namespace std; void test() { cout << "test" << endl; } main.cpp #include <iostream> using namespace std; int main() { return 0; } During linking I get the error multiple definition of test() - but how is that possible, considering that the two files have their own private scope!? I could understand it if I included the function prototype in each .cpp-files' corresponding header, but there is no such thing in this example.

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  • compiler warning at C++ template base class

    - by eike
    I get a compiler warning, that I don't understand in that context, when I compile the "Child.cpp" from the following code. (Don't wonder: I stripped off my class declarations to the bare minuum, so the content will not make much sense, but you will see the problem quicker). I get the warning with VS2003 and VS2008 on the highest warning level. The code AbstractClass.h : #include <iostream> template<typename T> class AbstractClass { public: virtual void Cancel(); // { std::cout << "Abstract Cancel" << std::endl; }; virtual void Process() = 0; }; //outside definition. if I comment out this and take the inline //definition like above (currently commented out), I don't get //a compiler warning template<typename T> void AbstractClass<T>::Cancel() { std::cout << "Abstract Cancel" << std::endl; } Child.h : #include "AbstractClass.h" class Child : public AbstractClass<int> { public: virtual void Process(); }; Child.cpp : #include "Child.h" #include <iostream> void Child::Process() { std::cout << "Process" << std::endl; } The warning The class "Child" is derived from "AbstractClass". In "AbstractClass" there's the public method "AbstractClass::Cancel()". If I define the method outside of the class body (like in the code you see), I get the compiler warning... AbstractClass.h(7) : warning C4505: 'AbstractClass::Cancel' : unreferenced local function has been removed with [T=int] ...when I compile "Child.cpp". I do not understand this, because this is a public function and the compiler can't know if I later reference this method or not. And, in the end, I reference this method, because I call it in main.cpp and despite this compiler warning, this method works if I compile and link all files and execute the program: //main.cpp #include <iostream> #include "Child.h" int main() { Child child; child.Cancel(); //works, despite the warning } If I do define the Cancel() function as inline (you see it as out commented code in AbstractClass.h), then I don't get the compiler warning. Of course my program works, but I want to understand this warning or is this just a compiler mistake? Furthermore, if do not implement AbsctractClass as a template class (just for a test purpose in this case) I also don't get the compiler warning...?

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  • When is #include <new> library required in C++?

    - by Czarak
    Hi, According to this reference entry for operator new ( http://www.cplusplus.com/reference/std/new/operator%20new/ ) : Global dynamic storage operator functions are special in the standard library: All three versions of operator new are declared in the global namespace, not in the std namespace. The first and second versions are implicitly declared in every translation unit of a C++ program: The header does not need to be included for them to be present. This seems to me to imply that the third version of operator new (placement new) is not implicitly declared in every translation unit of a C++ program and the header <new> does need to be included for it to be present. Is that correct? If so, how is it that using both g++ and MS VC++ Express compilers it seems I can compile code using the third version of new without #include <new> in my source code? Also, the MSDN Standard C++ Library reference entry on operator new gives some example code for the three forms of operator new which contains the #include <new> statement, however the example seems to compile and run just the same for me without this include? // new_op_new.cpp // compile with: /EHsc #include<new> #include<iostream> using namespace std; class MyClass { public: MyClass( ) { cout << "Construction MyClass." << this << endl; }; ~MyClass( ) { imember = 0; cout << "Destructing MyClass." << this << endl; }; int imember; }; int main( ) { // The first form of new delete MyClass* fPtr = new MyClass; delete fPtr; // The second form of new delete char x[sizeof( MyClass )]; MyClass* fPtr2 = new( &x[0] ) MyClass; fPtr2 -> ~MyClass(); cout << "The address of x[0] is : " << ( void* )&x[0] << endl; // The third form of new delete MyClass* fPtr3 = new( nothrow ) MyClass; delete fPtr3; } Could anyone shed some light on this and when and why you might need to #include <new> - maybe some example code that will not compile without #include <new> ? Thanks.

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  • On reference_wrapper and callable objects

    - by Nicola Bonelli
    Given the following callable object: struct callable : public std::unary_function &lt;void, void&gt; { void operator()() const { std::cout << "hello world" << std::endl; } }; a std::tr1::reference_wrapper< calls through it: callable obj; std::tr1::ref(obj)(); Instead, when the operator() accepts an argument: struct callable : public std::unary_function &lt;int, void&gt; { void operator()(int n) const { std::cout << n << std::endl; } }; std::tr1::bind accepts a reference_wrapper to it as a callable wrapper... callable obj; std::tr1::bind( std::tr1::ref(obj), 42 )(); but what's wrong with this? std::tr1::ref(obj)(42);

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  • C++ destructor seems to be called 'early'

    - by suicideducky
    Please see the "edit" section for the updated information. Sorry for yet another C++ dtor question... However I can't seem to find one exactly like mine as all the others are assigning to STL containers (that will delete objects itself) whereas mine is to an array of pointers. So I have the following code fragment #include<iostream> class Block{ public: int x, y, z; int type; Block(){ x=1; y=2; z=3; type=-1; } }; template <class T> class Octree{ T* children[8]; public: ~Octree(){ for( int i=0; i<8; i++){ std::cout << "del:" << i << std::endl; delete children[i]; } } Octree(){ for( int i=0; i<8; i++ ) children[i] = new T; } // place newchild in array at [i] void set_child(int i, T* newchild){ children[i] = newchild; } // return child at [i] T* get_child(int i){ return children[i]; } // place newchild at [i] and return the old [i] T* swap_child(int i, T* newchild){ T* p = children[i]; children[i] = newchild; return p; } }; int main(){ Octree< Octree<Block> > here; std::cout << "nothing seems to have broken" << std::endl; } Looking through the output I notice that the destructor is being called many times before I think it should (as Octree is still in scope), the end of the output also shows: del:0 del:0 del:1 del:2 del:3 Process returned -1073741819 (0xC0000005) execution time : 1.685 s Press any key to continue. For some reason the destructor is going through the same point in the loop twice (0) and then dying. All of this occures before the "nothing seems to have gone wrong" line which I expected before any dtor was called. Thanks in advance :) EDIT The code I posted has some things removed that I thought were unnecessary but after copying and compiling the code I pasted I no longer get the error. What I removed was other integer attributes of the code. Here is the origional: #include<iostream> class Block{ public: int x, y, z; int type; Block(){ x=1; y=2; z=3; type=-1; } Block(int xx, int yy, int zz, int ty){ x=xx; y=yy; z=zz; type=ty; } Block(int xx, int yy, int zz){ x=xx; y=yy; z=zz; type=0; } }; template <class T> class Octree{ int x, y, z; int size; T* children[8]; public: ~Octree(){ for( int i=0; i<8; i++){ std::cout << "del:" << i << std::endl; delete children[i]; } } Octree(int xx, int yy, int zz, int size){ x=xx; y=yy; z=zz; size=size; for( int i=0; i<8; i++ ) children[i] = new T; } Octree(){ Octree(0, 0, 0, 10); } // place newchild in array at [i] void set_child(int i, T* newchild){ children[i] = newchild; } // return child at [i] T* get_child(int i){ return children[i]; } // place newchild at [i] and return the old [i] T* swap_child(int i, T* newchild){ T* p = children[i]; children[i] = newchild; return p; } }; int main(){ Octree< Octree<Block> > here; std::cout << "nothing seems to have broken" << std::endl; } Also, as for the problems with set_child, get_child and swap_child leading to possible memory leaks this will be solved as a wrapper class will either use get before set or use swap to get the old child and write this out to disk before freeing the memory itself. I am glad that it is not my memory management failing but rather another error. I have not made a copy and/or assignment operator yet as I was just testing the block tree out, I will almost certainly make them all private very soon. This version spits out -1073741819. Thank you all for your suggestions and I apologise for highjacking my own thread :$

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  • GCC ICE -- alternative function syntax, variadic templates and tuples

    - by Marc H.
    (Related to C++0x, How do I expand a tuple into variadic template function arguments?.) The following code (see below) is taken from this discussion. The objective is to apply a function to a tuple. I simplified the template parameters and modified the code to allow for a return value of generic type. While the original code compiles fine, when I try to compile the modified code with GCC 4.4.3, g++ -std=c++0x main.cc -o main GCC reports an internal compiler error (ICE) with the following message: main.cc: In function ‘int main()’: main.cc:53: internal compiler error: in tsubst_copy, at cp/pt.c:10077 Please submit a full bug report, with preprocessed source if appropriate. See <file:///usr/share/doc/gcc-4.4/README.Bugs> for instructions. Question: Is the code correct? or is the ICE triggered by illegal code? // file: main.cc #include <tuple> // Recursive case template<unsigned int N> struct Apply_aux { template<typename F, typename T, typename... X> static auto apply(F f, const T& t, X... x) -> decltype(Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...)) { return Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...); } }; // Terminal case template<> struct Apply_aux<0> { template<typename F, typename T, typename... X> static auto apply(F f, const T&, X... x) -> decltype(f(x...)) { return f(x...); } }; // Actual apply function template<typename F, typename T> auto apply(F f, const T& t) -> decltype(Apply_aux<std::tuple_size<T>::value>::apply(f, t)) { return Apply_aux<std::tuple_size<T>::value>::apply(f, t); } // Testing #include <string> #include <iostream> int f(int p1, double p2, std::string p3) { std::cout << "int=" << p1 << ", double=" << p2 << ", string=" << p3 << std::endl; return 1; } int g(int p1, std::string p2) { std::cout << "int=" << p1 << ", string=" << p2 << std::endl; return 2; } int main() { std::tuple<int, double, char const*> tup(1, 2.0, "xxx"); std::cout << apply(f, tup) << std::endl; std::cout << apply(g, std::make_tuple(4, "yyy")) << std::endl; } Remark: If I hardcode the return type in the recursive case (see code), then everything is fine. That is, substituting this snippet for the recursive case does not trigger the ICE: // Recursive case (hardcoded return type) template<unsigned int N> struct Apply_aux { template<typename F, typename T, typename... X> static int apply(F f, const T& t, X... x) { return Apply_aux<N-1>::apply(f, t, std::get<N-1>(t), x...); } }; Alas, this is an incomplete solution to the original problem.

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  • About fork system call and global variables

    - by lurks
    I have this program in C++ that forks two new processes: #include <pthread.h> #include <iostream> #include <unistd.h> #include <sys/types.h> #include <sys/wait.h> #include <cstdlib> using namespace std; int shared; void func(){ extern int shared; for (int i=0; i<10;i++) shared++; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } int main(){ extern int shared; pid_t p1,p2; int status; shared=0; if ((p1=fork())==0) {func();exit(0);}; if ((p2=fork())==0) {func();exit(0);}; for(int i=0;i<10;i++) shared++; waitpid(p1,&status,0); waitpid(p2,&status,0);; cout<<"shared variable is: "<<shared<<endl; cout<<"Process "<<getpid()<<", shared " <<shared<<", &shared " <<&shared<<endl; } The two forked processes make an increment on the shared variables and the parent process does the same. As the variable belongs to the data segment of each process, the final value is 10 because the increment is independent. However, the memory address of the shared variables is the same, you can try compiling and watching the output of the program. How can that be explained ? I cannot understand that, I thought I knew how the fork() works, but this seems very odd.. I need an explanation on why the address is the same, although they are separate variables.

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  • Copy constructor demo (crashing... case 2)

    - by AKN
    Please have a glance at this program: class CopyCon { public: char *name; CopyCon() { name = new char[20]; name = "Hai";//_tcscpy(name,"Hai"); } CopyCon(const CopyCon &objCopyCon) { name = new char[_tcslen(objCopyCon.name)+1]; _tcscpy(name,objCopyCon.name); } ~CopyCon() { if( name != NULL ) { delete[] name; name = NULL; } } }; int main() { CopyCon obj1; CopyCon obj2(obj1); cout<<obj1.name<<endl; cout<<obj2.name<<endl; } This program crashes on execution. Error: "Expression: _BLOCK_TYPE_IS_VALID(pHead-nBlockUse)" If I assign "Hai" to name using aasignment operator, its crashing. Where as when I use string func _tcscpy to assign "Hai" to name, its working perfectly. Can some one explain why so?

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  • Simple vector program error

    - by Codeguru
    Hi iam new to c++ and iam trying out this vector program and i am getting the following error: error: conversion from test*' to non-scalar typetest' requested| Here is the code include include include include using namespace std; class test{ string s; vector <string> v; public: void read(){ ifstream in ("c://test.txt"); while(getline(in,s)) { v.push_back(s); } for(int i=0;i<v.size();i++) { cout<<v[i]<<"\n"; } } }; int main() { cout<<"Opening the file to read and displaying on the screen"< }

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  • Vectors of Pointers, inheritance

    - by user308553
    Hi I am a C++ beginner just encountered a problem I don't know how to fix I have two class, this is the header file: class A { public: int i; A(int a); }; class B: public A { public: string str; B(int a, string b); }; then I want to create a vector in main which store either class A or class B vector<A*> vec; A objectOne(1); B objectTwo(2, "hi"); vec.push_back(&objectOne); vec.push_back(&objectTwo); cout << vec.at(1)->i; //this is fine cout << vec.at(1)->str; //ERROR here I am really confused, I checked sites and stuff but I just don't know how to fix it, please help thanks in advance

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  • Trying to understand strtok

    - by Karthick
    Consider the following snippet that uses strtok to split the string madddy. char* str = (char*) malloc(sizeof("Madddy")); strcpy(str,"Madddy"); char* tmp = strtok(str,"d"); std::cout<<tmp; do { std::cout<<tmp; tmp=strtok(NULL, "dddy"); }while(tmp!=NULL); It works fine, the output is Ma. But by modifying the strtok to the following, tmp=strtok(NULL, "ay"); The output becomes Madd. So how does strtok exactly work? I have this question because I expected strtok to take each and every character that is in the delimiter string to be taken as a delimiter. But in certain cases it is doing that way but in few cases, it is giving unexpected results. Could anyone help me understand this?

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  • Accelerated C++, problem 5-6 (copying values from inside a vector to the front)

    - by Darel
    Hello, I'm working through the exercises in Accelerated C++ and I'm stuck on question 5-6. Here's the problem description: (somewhat abbreviated, I've removed extraneous info.) 5-6. Write the extract_fails function so that it copies the records for the passing students to the beginning of students, and then uses the resize function to remove the extra elements from the end of students. (students is a vector of student structures. student structures contain an individual student's name and grades.) More specifically, I'm having trouble getting the vector.insert function to properly copy the passing student structures to the start of the vector students. Here's the extract_fails function as I have it so far (note it doesn't resize the vector yet, as directed by the problem description; that should be trivial once I get past my current issue.) // Extract the students who failed from the "students" vector. void extract_fails(vector<Student_info>& students) { typedef vector<Student_info>::size_type str_sz; typedef vector<Student_info>::iterator iter; iter it = students.begin(); str_sz i = 0, count = 0; while (it != students.end()) { // fgrade tests wether or not the student failed if (!fgrade(*it)) { // if student passed, copy to front of vector students.insert(students.begin(), it, it); // tracks of the number of passing students(so we can properly resize the array) count++; } cout << it->name << endl; // output to verify that each student is iterated to it++; } } The code compiles and runs, but the students vector isn't adding any student structures to its front. My program's output displays that the students vector is unchanged. Here's my complete source code, followed by a sample input file (I redirect input from the console by typing " < grades" after the compiled program name at the command prompt.) #include <iostream> #include <string> #include <algorithm> // to get the declaration of `sort' #include <stdexcept> // to get the declaration of `domain_error' #include <vector> // to get the declaration of `vector' //driver program for grade partitioning examples using std::cin; using std::cout; using std::endl; using std::string; using std::domain_error; using std::sort; using std::vector; using std::max; using std::istream; struct Student_info { std::string name; double midterm, final; std::vector<double> homework; }; bool compare(const Student_info&, const Student_info&); std::istream& read(std::istream&, Student_info&); std::istream& read_hw(std::istream&, std::vector<double>&); double median(std::vector<double>); double grade(double, double, double); double grade(double, double, const std::vector<double>&); double grade(const Student_info&); bool fgrade(const Student_info&); void extract_fails(vector<Student_info>& v); int main() { vector<Student_info> vs; Student_info s; string::size_type maxlen = 0; while (read(cin, s)) { maxlen = max(maxlen, s.name.size()); vs.push_back(s); } sort(vs.begin(), vs.end(), compare); extract_fails(vs); // display the new, modified vector - it should be larger than // the input vector, due to some student structures being // added to the front of the vector. cout << "count: " << vs.size() << endl << endl; vector<Student_info>::iterator it = vs.begin(); while (it != vs.end()) cout << it++->name << endl; return 0; } // Extract the students who failed from the "students" vector. void extract_fails(vector<Student_info>& students) { typedef vector<Student_info>::size_type str_sz; typedef vector<Student_info>::iterator iter; iter it = students.begin(); str_sz i = 0, count = 0; while (it != students.end()) { // fgrade tests wether or not the student failed if (!fgrade(*it)) { // if student passed, copy to front of vector students.insert(students.begin(), it, it); // tracks of the number of passing students(so we can properly resize the array) count++; } cout << it->name << endl; // output to verify that each student is iterated to it++; } } bool compare(const Student_info& x, const Student_info& y) { return x.name < y.name; } istream& read(istream& is, Student_info& s) { // read and store the student's name and midterm and final exam grades is >> s.name >> s.midterm >> s.final; read_hw(is, s.homework); // read and store all the student's homework grades return is; } // read homework grades from an input stream into a `vector<double>' istream& read_hw(istream& in, vector<double>& hw) { if (in) { // get rid of previous contents hw.clear(); // read homework grades double x; while (in >> x) hw.push_back(x); // clear the stream so that input will work for the next student in.clear(); } return in; } // compute the median of a `vector<double>' // note that calling this function copies the entire argument `vector' double median(vector<double> vec) { typedef vector<double>::size_type vec_sz; vec_sz size = vec.size(); if (size == 0) throw domain_error("median of an empty vector"); sort(vec.begin(), vec.end()); vec_sz mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } // compute a student's overall grade from midterm and final exam grades and homework grade double grade(double midterm, double final, double homework) { return 0.2 * midterm + 0.4 * final + 0.4 * homework; } // compute a student's overall grade from midterm and final exam grades // and vector of homework grades. // this function does not copy its argument, because `median' does so for us. double grade(double midterm, double final, const vector<double>& hw) { if (hw.size() == 0) throw domain_error("student has done no homework"); return grade(midterm, final, median(hw)); } double grade(const Student_info& s) { return grade(s.midterm, s.final, s.homework); } // predicate to determine whether a student failed bool fgrade(const Student_info& s) { return grade(s) < 60; } Sample input file: Moo 100 100 100 100 100 100 100 100 Fail1 45 55 65 80 90 70 65 60 Moore 75 85 77 59 0 85 75 89 Norman 57 78 73 66 78 70 88 89 Olson 89 86 70 90 55 73 80 84 Peerson 47 70 82 73 50 87 73 71 Baker 67 72 73 40 0 78 55 70 Davis 77 70 82 65 70 77 83 81 Edwards 77 72 73 80 90 93 75 90 Fail2 55 55 65 50 55 60 65 60 Thanks to anyone who takes the time to look at this!

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  • C++ password masking

    - by blaxc
    hi... i'm writing a code to receive password input. Below is my code... the program run well but the problem is other keys beside than numerical and alphabet characters also being read, for example delete, insert, and etc. can i know how can i avoid it? tq... string pw=""; char c=' '; while(c != 13) //Loop until 'Enter' is pressed { c = _getch(); if(c==13) break; if(c==8) { if(pw.size()!=0) //delete only if there is input { cout<<"\b \b"; pw.erase(pw.size()-1); } } if((c>47&&c<58)||(c>64&&c<91)||(c>96&&c<123)) //ASCii code for integer and alphabet { pw += c; cout << "*"; } }

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  • How does sizeof calculate the size of structures

    - by Gearoid Murphy
    I know that a char and an int are calculated as being 8 bytes on 32 bit architectures due to alignment, but I recently came across a situation where a structure with 3 shorts was reported as being 6 bytes by the sizeof operator. Code is as follows: #include <iostream> using namespace std ; struct IntAndChar { int a ; unsigned char b ; }; struct ThreeShorts { unsigned short a ; unsigned short b ; unsigned short c ; }; int main() { cout<<sizeof(IntAndChar)<<endl; // outputs '8' cout<<sizeof(ThreeShorts)<<endl; // outputs '6', I expected this to be '8' return 0 ; } Compiler : g++ (Debian 4.3.2-1.1) 4.3.2. This really puzzles me, why isn't alignment enforced for the structure containing 3 shorts?

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  • Good input validation loop using cin - C++

    - by Alex
    Hi there, I'm in my second OOP class, and my first class was taught in C#, so I'm new to C++ and currently I am practicing input validation using cin. So here's my question: Is this loop I constructed a pretty good way of validating input? Or is there a more common/accepted way of doing it? Thanks! Code: int taxableIncome; int error; // input validation loop do { error = 0; cout << "Please enter in your taxable income: "; cin >> taxableIncome; if (cin.fail()) { cout << "Please enter a valid integer" << endl; error = 1; cin.clear(); cin.ignore(80, '\n'); } }while(error == 1);

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  • Cpp some basic problems

    - by DevAno1
    Hello. My task was as follows : Create class Person with char*name and int age. Implement contructor using dynamic allocation of memory for variables, destructor, function init and friend function show. Then transform this class to header and cpp file and implement in other program. Ok so I've almost finished my Person class, but I get error after destructor. First question is how to write this properly ? #include <iostream> using namespace std; class Person { char* name; int age; public: int * take_age(); Person(){ int size=0; cout << "Give length of char*" << endl; cin >> size; name = new char[size]; age = 0; } ~Person(){ cout << "Destroying resources" << endl; delete *[] name; delete * take_age(); } friend void(Person &p); int * Person::take_age(){ return age; } void init(char* n, int a) { name = n; age = a; } void show(Person &p){ cout << "Name: " << p.name << "," << "age: " << p.age << endl; } }; int main(void) { Person *p = new Person; p->init("Mary", 25); p.show(); system("PAUSE"); return 0; } And now with header/implementation part : - do I need to introduce constructor in header/implementation files ? If yes - how? - my show() function is a friendly function. Should I take it into account somehow ? I already failed to return this task on my exam, but still I'd like to know how to implement it.

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  • C++ and Scripting.Dictionary from scrrun.dll

    - by MaxFX
    Hello. I have some trouble with Scripting.Dictionary in C++. I'm trying to use interface IDictionary via smart pointer but methods of creating object don't work and I can't understand why. CoInitialize(NULL); IDictionaryPtr dict; dict.CreateInstance(__uuidof(Dictionary)); _variant_t num1 = 1; _variant_t num2 = 2; dict->Add(&num1, &num2); long i; dict->get_Count(&i); cout << i << "\n"; But method Add does not work and cout of elements in dictionary is always 0. How correct to use Scripting.Dictionary in that case. PS.: I'm getting Scripting interfaces by #import "scrrun.dll"

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