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  • Returning reference to object is not changing the address in c++

    - by ashish-sangwan
    I am trying to understand functions returning a reference. For that I have written a simple program: #include<iostream> using namespace std; class test { int i; friend test& func(); public: test(int j){i=j;} void show(){cout<<i<<endl;} }; test& func() { test temp(10); return temp; //// Address of temp=0xbfcb2874 } int main() { test obj1(50); // Address of obj1=0xbfcb28a0 func()=obj1; <= Problem:The address of obj1 is not changing obj1.show(); // // Address of obj1=0xbfcb28a0 return 0; } I ran the program using gdb and observed that the address of obj1 still remains same, but I expect it to get changed to 0xbfcb2874. I am not clear with the concept. Please help.

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  • On C++ global operator new: why it can be replaced

    - by Jimmy
    I wrote a small program in VS2005 to test whether C++ global operator new can be overloaded. It can. #include "stdafx.h" #include "iostream" #include "iomanip" #include "string" #include "new" using namespace std; class C { public: C() { cout<<"CTOR"<<endl; } }; void * operator new(size_t size) { cout<<"my overload of global plain old new"<<endl; // try to allocate size bytes void *p = malloc(size); return (p); } int main() { C* pc1 = new C; cin.get(); return 0; } In the above, my definition of operator new is called. If I remove that function from the code, then operator new in C:\Program Files (x86)\Microsoft Visual Studio 8\VC\crt\src\new.cpp gets called. All is good. However, in my opinion, my implementations of operator new does NOT overload the new in new.cpp, it CONFLICTS with it and violates the one-definition rule. Why doesn't the compiler complain about it? Or does the standard say since operator new is so special, one-definition rule does not apply here? Thanks.

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  • C++ class with char pointers returning garbage

    - by JMP
    I created a class "Entry" to handle Dictionary entries, but in my main(), I create the Entry() and try to cout the char typed public members, but I get garbage. When I look at the Watch list in debugger, I see the values being set, but as soon as I access the values, there is garbage. Can anyone elaborate on what I might be missing? #include <iostream> using namespace std; class Entry { public: Entry(const char *line); char *Word; char *Definition; }; Entry::Entry(const char *line) { char tmp[100]; strcpy(tmp, line); Word = strtok(tmp, ",") + '\0'; Definition = strtok(0,",") + '\0'; } int main() { Entry *e = new Entry("drink,What you need after a long day's work"); cout << "Word: " << e->Word << endl; cout << "Def: " << e->Definition << endl; cout << endl; delete e; e = 0; return 0; }

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  • C++ program crashes at runtime

    - by qwerty
    Hello, I have this simple c++ program #include <cstdlib> #include <iostream> #include <math.h> #include <stdlib.h> #include <time.h> #include <vector> using namespace std; int aleator(int n) { return (rand()%n)+1; } int main() { int r; int indexes[100]={0}; // const int size=100; //int a[size]; std::vector<int>v; srand(time(0)); for (int i=0;i<25;i++) { int index = aleator(100); if (indexes[index] != 0) { // try again i--; continue; } indexes[index] = 1; cout << v[index] ; } cout<<" "<<endl; system("pause"); return 0; } But at runtime it crashes, so i got that error with 'Send error report' and 'Don't send'. What i'm doing wrong? Thanks!

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  • Prog error: for replacing spaces with "%20"

    - by assasinC
    below is the prog i am compiling for replacing spaces with "%20" but when I run it output window shows blank and a message "arrays5.exe has occurred a prob" #include <iostream> #include<cstring> using namespace std; void method(char str[], int len) //replaces spaces with "%20" { int spaces, newlen,i; for (i=0;i<len;i++) if(str[i]==' ') spaces++; newlen=len+spaces*2; str[newlen]=0; for (i=len-1;i>=0;i--) { if(str[i]==' ') { str[newlen-1]='0'; str[newlen-2]='2'; str[newlen-3]='%'; newlen=newlen-3; } else { str[newlen-1]=str[i]; newlen=newlen-1; } } } int main() { char str[20]="sa h "; method(str,5); cout <<str<<endl; return 0; } Please help me finding the error.Thanks

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  • give feedback on this pointer program

    - by JohnWong
    This is relatively simple program. But I want to get some feedback about how I can improve this program (if any), for example, unnecessary statements? #include<iostream> #include<fstream> using namespace std; double Average(double*,int); int main() { ifstream inFile("data2.txt"); const int SIZE = 4; double *array = new double(SIZE); double *temp; temp = array; for (int i = 0; i < SIZE; i++) { inFile >> *array++; } cout << "Average is: " << Average(temp, SIZE) << endl; } double Average(double *pointer, int x) { double sum = 0; for (int i = 0; i < x; i++) { sum += *pointer++; } return (sum/x); } The codes are valid and the program is working fine. But I just want to hear what you guys think, since most of you have more experience than I do (well I am only a freshman ... lol) Thanks.

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  • C++ STL: How to write wrappers for cout, cerr, cin and endl?

    - by Ashwin
    I do not like using namespace std, but I am also tired of having to type std:: in front of every cout, cin, cerr and endl. So, I thought of giving them shorter new names like this: // STLWrapper.h #include <iostream> #include <string> extern std::ostream& Cout; extern std::ostream& Cerr; extern std::istream& Cin; extern std::string& Endl; // STLWrapper.cpp #include "STLWrapper.h" std::ostream& Cout = std::cout; std::ostream& Cerr = std::cerr; std::istream& Cerr = std::cin; std::string _EndlStr("\n"); std::string& Endl = _EndlStr; This works. But, are there any problems in the above which I am missing? Is there a better way to achieve the same?

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  • how do i save time to a file?

    - by blood
    hi, i have a program that saves data to file and i want to put a time stamp of the current date/time on that log but when i try to write the time to the file it will not show up. #include <iostream> #include <windows.h> #include <fstream> #include <string> #include <sstream> #include <direct.h> #include <stdio.h> #include <time.h> using namespace std; string header_str = ("NULL"); int main() { for(;;) { stringstream header(stringstream::in | stringstream::out); header << "datasdasdasd_"; time_t rawtime; time ( &rawtime ); header << ctime (&rawtime); header_str = header.str(); fstream filestr; filestr.open ("C:\\test.txt", fstream::in | fstream::out | fstream::app | ios_base::binary | ios_base::out); for(;;) { filestr << (header_str); } filestr.close(); } return 0; } anyone know how to fix this?

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  • Saving results to a file in C++

    - by user1680877
    I have a problem with this code. What I am looking for in the code is to get the result of "first" and "second" randomly and put the result in a file. It works great if I run it without using the file and I get all the correct results, but when I try to save the result in the file, I get only the first node which contains (first, secnd). Here is the code: #include<iostream> #include <fstream> #include<cmath> using namespace std; void main() { int first[100],secnd[100]; for (int i=0; i<100 ;i++) { first[i]=rand()%500; //random number from to 499 secnd[i]=rand()%500; //random number from to 499 ofstream myfile; myfile.open ("example.txt"); myfile << "Writing this to a file.\n"; myfile <<first[i]<<" "<<secnd[i]; myfile.close(); } }

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  • How does does ifstream eof() work?

    - by Chan
    Hello everyone, #include <vector> #include <list> #include <map> #include <set> #include <deque> #include <stack> #include <bitset> #include <algorithm> #include <functional> #include <numeric> #include <utility> #include <sstream> #include <iostream> #include <iomanip> #include <cstdio> #include <cmath> #include <cstdlib> #include <ctime> #include <cctype> #include <fstream> using namespace std; int main() { fstream inf( "ex.txt", ios::in ); while( !inf.eof() ) { std::cout << inf.get() << "\n"; } inf.close(); inf.clear(); inf.open( "ex.txt", ios::in ); char c; while( inf >> c ) { std::cout << c << "\n"; } return 0; } I'm really confused about eof() function. Suppose my ex.txt's content is: abc It always reads an extra character and show -1. when reading using eof()? But the inf c gave the correct output which was 'abc'? Can anyone help me explain this? Best regards, Chan Nguyen

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  • C++: Construction and initialization order guarantees

    - by Helltone
    Hi, I have some doubts about construction and initialization order guarantees in C++. For instance, the following code has four classes X, Y, Z and W. The main function instantiates an object of class X. X contains an object of class Y, and derives from class Z, so both constructors will be called. Additionally, the const char* parameter passed to X's constructor will be implicitly converted to W, so W's constructor must also be called. What are the guarantees the C++ standard gives on the order of the calls to the copy constructors? Or, equivalently, this program is allowed to print? #include <iostream> class Z { public: Z() { std::cout << "Z" << std::endl; } }; class Y { public: Y() { std::cout << "Y" << std::endl; } }; class W { public: W(const char*) { std::cout << "W" << std::endl; } }; class X : public Z { public: X(const W&) { std::cout << "X" << std::endl; } private: Y y; }; int main(int, char*[]) { X x("x"); return 0; }

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  • Compile time type determination in C++

    - by dicroce
    A coworker recently showed me some code that he found online. It appears to allow compile time determination of whether a type has an "is a" relationship with another type. I think this is totally awesome, but I have to admit that I'm clueless as to how this actually works. Can anyone explain this to me? template<typename BaseT, typename DerivedT> inline bool isRelated(const DerivedT&) { DerivedT derived(); char test(const BaseT&); // sizeof(test()) == sizeof(char) char (&test(...))[2]; // sizeof(test()) == sizeof(char[2]) struct conversion { enum { exists = (sizeof(test(derived())) == sizeof(char)) }; }; return conversion::exists; } Once this function is defined, you can use it like this: #include <iostream> class base {}; class derived : public base {}; class unrelated {}; int main() { base b; derived d; unrelated u; if( isRelated<base>( b ) ) std::cout << "b is related to base" << std::endl; if( isRelated<base>( d ) ) std::cout << "d is related to base" << std::endl; if( !isRelated<base>( u ) ) std::cout << "u is not related to base" << std::endl; }

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  • overloading "<<" with a struct (no class) cout style

    - by monkeyking
    I have a struct that I'd like to output using either 'std::cout' or some other output stream. Is this possible without using classes? Thanks #include <iostream> #include <fstream> template <typename T> struct point{ T x; T y; }; template <typename T> std::ostream& dump(std::ostream &o,point<T> p) const{ o<<"x: " << p.x <<"\ty: " << p.y <<std::endl; } template<typename T> std::ostream& operator << (std::ostream &o,const point<T> &a){ return dump(o,a); } int main(){ point<double> p; p.x=0.1; p.y=0.3; dump(std::cout,p); std::cout << p ;//how? return 0; } I tried different syntax' but I cant seem to make it work.

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  • how to Clean up(destructor) a dynamic Array of pointers??

    - by Ahmed Sharara
    Is that Destructor is enough or do I have to iterate to delete the new nodes?? #include "stdafx.h" #include<iostream> using namespace std; struct node{ int row; int col; int value; node* next_in_row; node* next_in_col; }; class MultiLinkedListSparseArray { private: char *logfile; node** rowPtr; node** colPtr; // used in constructor node* find_node(node* out); node* ins_node(node* ins,int col); node* in_node(node* ins,node* z); node* get(node* in,int row,int col); bool exist(node* so,int row,int col); //add anything you need public: MultiLinkedListSparseArray(int rows, int cols); ~MultiLinkedListSparseArray(); void setCell(int row, int col, int value); int getCell(int row, int col); void display(); void log(char *s); void dump(); }; MultiLinkedListSparseArray::MultiLinkedListSparseArray(int rows,int cols){ rowPtr=new node* [rows+1]; colPtr=new node* [cols+1]; for(int n=0;n<=rows;n++) rowPtr[n]=NULL; for(int i=0;i<=cols;i++) colPtr[i]=NULL; } MultiLinkedListSparseArray::~MultiLinkedListSparseArray(){ // is that destructor enough?? cout<<"array is deleted"<<endl; delete [] rowPtr; delete [] colPtr; }

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  • Should I delete the string members of a C++ class?

    - by Bobby
    If I have the following declaration: #include <iostream> #include <string> class DEMData { private: int bitFldPos; int bytFldPos; std::string byteOrder; std::string desS; std::string engUnit; std::string oTag; std::string valType; int idx; public: DEMData(); DEMData(const DEMData &d); void SetIndex(int idx); int GetIndex() const; void SetValType(const char* valType); const char* GetValType() const; void SetOTag(const char* oTag); const char* GetOTag() const; void SetEngUnit(const char* engUnit); const char* GetEngUnit() const; void SetDesS(const char* desS); const char* GetDesS() const; void SetByteOrder(const char* byteOrder); const char* GetByteOrder() const; void SetBytFldPos(int bytFldPos); int GetBytFldPos() const; void SetBitFldPos(int bitFldPos); int GetBitFldPos() const; friend std::ostream &operator<<(std::ostream &stream, DEMData d); bool operator==(const DEMData &d) const; ~DEMData(); }; what code should be in the destructor? Should I "delete" the std::string fields?

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  • C++ UTF-8 output with ICU

    - by Isaac
    I'm struggling to get started with the C++ ICU library. I have tried to get the simplest example to work, but even that has failed. I would just like to output a UTF-8 string and then go from there. Here is what I have: #include <unicode/unistr.h> #include <unicode/ustream.h> #include <iostream> int main() { UnicodeString s = UNICODE_STRING_SIMPLE("??????"); std::cout << s << std::endl; return 0; } Here is the output: $ g++ -I/sw/include -licucore -Wall -Werror -o icu_test main.cpp $ ./icu_test пÑÐ¸Ð²ÐµÑ My terminal and font support UTF-8 and I regularly use the terminal with UTF-8. My source code is in UTF-8. I think that perhaps I somehow need to set the output stream to UTF-8 because ICU stores strings as UTF-16, but I'm really not sure and I would have thought that the operators provided by ustream.h would do that anyway. Any help would be appreciated, thank you.

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  • CURL C API: callback was not called

    - by Pierre
    Hi all, The code below is a test for the CURL C API . The problem is that the callback function write_callback is never called. Why ? /** compilation: g++ source.cpp -lcurl */ #include <assert.h> #include <iostream> #include <cstdlib> #include <cstring> #include <cassert> #include <curl/curl.h> using namespace std; static size_t write_callback(void *ptr, size_t size, size_t nmemb, void *userp) { std::cerr << "CALLBACK WAS CALLED" << endl; exit(-1); return size*nmemb; } static void test_curl() { int any_data=1; CURLM* multi_handle=NULL; CURL* handle_curl = ::curl_easy_init(); assert(handle_curl!=NULL); ::curl_easy_setopt(handle_curl, CURLOPT_URL, "http://en.wikipedia.org/wiki/Main_Page"); ::curl_easy_setopt(handle_curl, CURLOPT_WRITEDATA, &any_data); ::curl_easy_setopt(handle_curl, CURLOPT_VERBOSE, 1); ::curl_easy_setopt(handle_curl, CURLOPT_WRITEFUNCTION, write_callback); ::curl_easy_setopt(handle_curl, CURLOPT_USERAGENT, "libcurl-agent/1.0"); multi_handle = ::curl_multi_init(); assert(multi_handle!=NULL); ::curl_multi_add_handle(multi_handle, handle_curl); int still_running=0; /* lets start the fetch */ while(::curl_multi_perform(multi_handle, &still_running) == CURLM_CALL_MULTI_PERFORM ); std::cerr << "End of curl_multi_perform."<< endl; //cleanup should go here ::exit(EXIT_SUCCESS); } int main(int argc,char** argv) { test_curl(); return 0; } Many thanks Pierre

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  • C++ template member specialization - is this a compiler limitation?

    - by LoudNPossiblyRight
    Is it possible to do this kind of specialization? If so, how? The specialization in question is marked //THIS SPECIALIZATION WILL NOT COMPILE I have used VS2008, VS2010, gcc 4.4.3 and neither can compile this. #include<iostream> #include<string> using namespace std; template <typename ALPHA> class klass{ public: template <typename BETA> void func(BETA B); }; template <typename ALPHA> template <typename BETA> void klass<ALPHA>::func(BETA B){ cout << "I AM A BETA FUNC: " << B <<endl; } //THIS SPECIALIZATION WILL NOT COMPILE template <typename ALPHA> template <> void klass<ALPHA>::func(string B){ cout << "I AM A SPECIAL BETA FUNC: " << B <<endl; } int main(){ klass<string> k; k.func(1); k.func("hello"); return 0; }

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  • Segmentation fault on returning from main (very short and simple code, no arrays or pointers)

    - by Gábor Kovács
    I've been wondering why the following trivial code produces a segmentation fault when returning from main(): //Produces "Error while dumping state (probably corrupted stack); Segmentation fault" #include <iostream> #include <fstream> #include <vector> using namespace std; class Test { vector<int> numbers; }; int main() { Test a; ifstream infile; cout << "Last statement..." << endl; // this gets executed return 0; } Interestingly, 1) if only one of the two variables is declared, I don't get the error, 2) if I declare a vector variable instead of an object with a vector member, everything's fine, 3) if I declare an ofstream instead of an ifstream, again, everything works fine. Something appears to be wrong with this specific combination... Could this be a compiler bug? I use gcc version 3.4.4 with cygwin. Thanks for the tips in advance. Gábor

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  • The program fails to display `cout` when it is run

    - by Jeff - FL
    Hello, I justed started a C++ course & I wrote, compiled, debugged & ran my first program: // This program calculates how much a little league team spent last year to purchase new baseballs. #include <iostream> using namespace std; int baseballs; int cost; int total; int main() { baseballs, cost, total; // Get the number of baseballs were purchased. cout << "How many baseballs were purchased? "; cin >> baseballs; // Get the cost of baseballs purchased. cout << "What was the cost of each baseball purchased? "; cin >> cost; // Calculate the total. total = baseballs * cost; // Display the total. cout << "The total amount spent $" << total << endl; return 0; } The only probelm that I encountered was that when I ran the program it failed to display the total amount spent (cout). Could someone please explain why? Thanks Jeff H - Sarasota, FL

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  • Path String Concatenation 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() ) { cout<< "success\n"; } myLibFile.close(); } } myfile.close(); } else cout << "Unable to open file"; return 0; } Assume my [Config.txt] include the content below. And all the *.txt files located in libs folder. file1.txt file2.txt file3.txt

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  • Console in VS 2012 Express for C++?

    - by Live2Code
    I'm very new to programming, so be nice. I was using Eclipse for C/C++ devs for a while, but it seemed quite buggy so I was advised to switch to Visual Studio Express. I'm just testing out with a simple "Hello World" program #include <iostream> #include <string> using namespace std; int main( int argc, char ** argv ) { string response; cout << "Gimme a string: " << flush; cin >> response; cout << "The string is: " << response << endl; system("pause"); return 0; } not much to go wrong there anyway, I noticed that there is no "console" like in Eclipse. All of the text pops up in a little command prompt window. And, also, this window closes right after displaying new text if there is no other things to do after it (like a cin). I have been told that I can use system("pause") but there has to be a better way. In Eclipse, the text would not suddenly disappear because the console window closed. i know this question might be a little confusing, comment and I'll try to explain what I'm saying. Or paste the codes into your Visual Studio 2012 Express Edition. But is there a way to display all of my text and whatever in a "console" as opposed to a command prompt-type window; and why does it always close before I can read the last thing?

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  • Specializing function templates outside class temp. definition - what is the correct way of doing t

    - by LoudNPossiblyRight
    I am attempting to specialize a function template that is a member of a template class. The two of them have different template parameters. The template function specialization inside the temp. class definition is never called and the one func. spec. outside the class definition does not even compile. Should i expect this to work in the first place, and if so, what do i have to change in this code to both compile and make it work correctly: using VS2010 #include<iostream> using namespace std; template <typename T> class klass{ public: template <typename U> void func(const U &u){ cout << "I AM A TEMPLATE FUNC" << endl; } //THIS NEVER GETS CALLED !!! template <> void klass<T>::func(const string &s){ cout << "I AM A STRING SPECIALIST" << endl; } }; //THIS SPECIALIZATION WILL NOT COMPILE !!! template <typename T> template <> void klass<T>::func(const double &s){ cout << "I AM A DOUBLE SPECIALIST" << endl; } int main(){ double d = 3.14159265; klass<int> k; k.func(1234567890); k.func("string"); k.func(3.14159265); return 0; }

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  • Pointing class property to another class with vectors

    - by jmclem
    I've got a simple class, and another class that has a property that points to the first class: #include <iostream> #include <vector> using namespace std; class first{ public: int var1; }; class second{ public: first* classvar; }; Then, i've got a void that's supposed to point "classvar" to the intended iteration of the class "first". void fill(vector<second>& sec, vector<first>& fir){ sec[0].classvar = &fir[0]; } Finally the main(). Create and fill a vector of class "first", create "second" vector, and run the fill function. int main(){ vector<first> a(1); a[0].var1 = 1000; vector<second> b(1); fill(b, a); cout << b[0].classvar.var1 << '\n'; system("PAUSE"); return 0; } This gives me the following error: 1>c:\...\main.cpp(29) : error C2228: left of '.var1' must have class/struct/union 1> type is 'first *' And I can't figure out why it reads the "classvar" as the whole vector instead of just the single instance. Should I do this cout << b[0].classvar[0].var1 << '\n'; it reads perfectly. Can anyone figure out the problem? Thanks in advance

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  • No "redefinition of default parameter error" for class template member function?

    - by STingRaySC
    Why does the following give no compilation error?: // T.h template<class T> class X { public: void foo(int a = 42); }; // Main.cpp #include "T.h" #include <iostream> template<class T> void X<T>::foo(int a = 13) { std::cout << a << std::endl; } int main() { X<int> x; x.foo(); // prints 42 } It seems as though the 13 is just silently ignored by the compiler. Why is this? The cooky thing is that if the template declaration is in Main.cpp instead of a header file, I do indeed get the default parameter redefinition error. Now I know the compiler will complain about this if it were just an ordinary (non-template) function. What does the standard have to say about default parameters in class template member functions or function templates?

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