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  • How to negate a predicate function using operator ! in C++?

    - by Chan
    Hi, I want to erase all the elements that do not satisfy a criterion. For example: delete all the characters in a string that are not digit. My solution using boost::is_digit worked well. struct my_is_digit { bool operator()( char c ) const { return c >= '0' && c <= '9'; } }; int main() { string s( "1a2b3c4d" ); s.erase( remove_if( s.begin(), s.end(), !boost::is_digit() ), s.end() ); s.erase( remove_if( s.begin(), s.end(), !my_is_digit() ), s.end() ); cout << s << endl; return 0; } Then I tried my own version, the compiler complained :( error C2675: unary '!' : 'my_is_digit' does not define this operator or a conversion to a type acceptable to the predefined operator I could use not1() adapter, however I still think the operator ! is more meaningful in my current context. How could I implement such a ! like boost::is_digit() ? Any idea? Thanks, Chan Nguyen

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  • C++: Declare static variable in function argument list

    - by MDC
    Is there any way at all in C++ to declare a static variable while passing it to a function? I'm looking to use a macro to expand to the expression passed to the function. The expression needs to declare and initialize a static variable on that particular line (based on the filename and line number using FILE and LINE). int foo(int b) { int c = b + 2; return c; } int main() { int a = 3; a = foo(static int h = 2); //<---- see this! cout << a; return 0; } The problem I'm trying to solve is getting the filename and line number with the FILE and LINE macros provided by the preprocessor, but then creating a lookup table with integer keys leading to the FILE, LINE pairs. For example, the key 89 may map to file foo.cpp, line 20. To get this to work, I'm trying to use local static variables, so that they are initialized only once per line execution. The static variable will be initialized by calling a function that calculates the integer key and adds an entry to the lookup table if it is not there. Right now the program uses a message class to send exception information. I'm writing a macro to wrap this class into a new class: WRAPPER_MACRO(old_class_object) will expand to NewClass(old_class_object, key_value). If I add the static variable declaration as a second line right before this, it should work. The problem is that in most places in the code, the old class object is passed as an argument to a function. So the problem becomes declaring and initializing the static variable somehow with the macro, while keeping the existing function calls.

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  • LNK1104: cannot open file 'kernel32.lib'

    - by Geoff
    I Had VS2010 installed but found that intellisense wasn't working. I looked on the web and found that I wasn't the only one who had that issue. So, I installed VS2008 and everything was fine. Then I decided to clean up my computer and removed VS2010 and immediately started getting this error on my programs (new and old). Even a simple test program that has one cout command. I tried repairing VS2008 and that didn't work so I tried to uninstall and then reinstall and still I am getting the same problem. I have looked online for this issue and though I have found a lot of other people are experiencing this issue it is not the same. They are having problems with other external references, not the ones that should automatically be included like kernel32 and lib32 etc. I also tried the solution that worked for some people with their other references and I included the path (with and without quotes) to my kernel32 directory but still I get the same problem, or in some instances I will get LNK1104: cannot open file 'C:\WINDOWS\system32.obj' with and without quotes in the linker config. Can anyone please help?

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  • Crash in C++ Code

    - by Ankuj
    I am trying to list all files in a directory recursively. But my code crashes without giving any error. When the given file is directory I recursively call the function or else print its name. I am using dirent.h int list_file(string path) { DIR *dir; struct dirent *ent; char *c_style_path; c_style_path = new char[path.length()]; c_style_path = (char *)path.c_str(); dir = opendir (c_style_path); if (dir != NULL) { /* print all the files and directories within directory */ while ((ent = readdir (dir)) != NULL) { if(ent->d_type == DT_DIR && (strcmp(ent->d_name,".")!=0) && (strcmp(ent->d_name,"..")!=0)) { string tmp = path + "\\" + ent->d_name; list_file(tmp); } else { cout<<ent->d_name<<endl; } } closedir (dir); } else { /* could not open directory */ perror (""); return EXIT_FAILURE; } delete [] c_style_path; return 0; } I am not getting as to what I am doing wrong here. Any clues ?

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  • How to get readable classname and title from HWND handle? in WinApi c++

    - by Marko29
    I am using the following enumchild proc to get hwnd of each window, the problem is that i am unable to somehow detect any info from each hwnd so i can do what i want with the ones that are detected as the ones i need. For example, how could i get window class name and the title of each window in the enum bellow? I tried something like.. BOOL CALLBACK EnumChildProc(HWND hwnd, LPARAM lParam) { TCHAR className[MAX_PATH]; GetClassName(hwnd, cName, _countof(cName)); cout << cName; return TRUE; } It just returns the hexadec handle info and every single time it is same, shouldnt the GetClassName func change the cName into new handle each time? Also GetClassName function returns number of chars written to cName, i dont really see how this is useful to me? I need to get my cName in some readable format so i can do something like if(cName == TEXT("classnameiamlookingfor" && hwndtitle = TEXT("thetitlethatinterestsme") DOSOMETHINGWITHIT(); But all i get here is hexadec mess.

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  • Is std::move really needed on initialization list of constructor for heavy members passed by value?

    - by PiotrNycz
    Recently I read an example from cppreference.../vector/emplace_back: struct President { std::string name; std::string country; int year; President(std::string p_name, std::string p_country, int p_year) : name(std::move(p_name)), country(std::move(p_country)), year(p_year) { std::cout << "I am being constructed.\n"; } My question: is this std::move really needed? My point is that compiler sees that this p_name is not used in the body of constructor, so, maybe, there is some rule to use move semantics for it by default? That would be really annoying to add std::move on initialization list to every heavy member (like std::string, std::vector). Imagine hundreds of KLOC project written in C++03 - shall we add everywhere this std::move? This question: move-constructor-and-initialization-list answer says: As a golden rule, whenever you take something by rvalue reference, you need to use it inside std::move, and whenever you take something by universal reference (i.e. deduced templated type with &&), you need to use it inside std::forward But I am not sure: passing by value is rather not universal reference?

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  • write a program that prompts the user to input five decimal numbers

    - by user312309
    This is the question. write a program that prompts the user to input five decimal numbers. the program should then add the five decimal numbers, convert the sum to the nearest integer,m and print the result. This is what I've gotten so far: // p111n9.cpp : Defines the entry point for the console application. // #include <iostream> using namespace std; double a, b , c , d , e, f; int main(int argc, char* argv[]) { cout << "enter 5 decimals: " << endl; cin >> a >> b >> c >> d >> e; f = a + b + c + d + e; return 0; } Now I just need to convert the sum(f) to the nearest integer, m and print the result. How do I do this?

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  • Append to the end of a Char array in C++

    - by Taylor Huston
    Is there a command that can append one array of char onto another? Something that would theoretically work like this: //array1 has already been set to "The dog jumps " //array2 has already been set to "over the log" append(array2,array1); cout << array1; //would output "The dog jumps over the log"; This is a pretty easy function to make I would think, I am just surprised there isn't a built in command for it. *Edit I should have been more clear, I didn't mean changing the size of the array. If array1 was set to 50 characters, but was only using 10 of them, you would still have 40 characters to work with. I was thinking an automatic command that would essentially do: //assuming array1 has 10 characters but was declared with 25 and array2 has 5 characters int i=10; int z=0; do{ array1[i] = array2[z]; ++i; ++z; }while(array[z] != '\0'); I am pretty sure that syntax would work, or something similar.

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  • Is it possible to create ostream object, which outputs to multiple destinations?

    - by fiktor
    In 0-th approximation I have a class class MyClass{ public: ... std::ostream & getOStream(){return f;} private: ofstream f; ... }; Which is used sometimes in the following way: MyClass myclass; myclass.getOStream()<<some<<information<<printed<<here; But now I want to change the class MyClass, so that information will be printed both to f and to std::out, i.e. I want the above line to be equivalent to myclass.f<<some<<information<<printed<<here; std::cout<<some<<information<<printed<<here; I don't know any good way to do that. Do you? Is there any standard solution (for example in stl or in boost)? P.S. I tried to search on this, but it seems that I don't know good keywords. Words multiple, output, ostream, C++, boost seem to be too general.

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  • Does std::vector change its address? How to avoid

    - by kunigami
    Since vector elements are stored contiguously, I guess it may not have the same address after some push_back's , because the initial allocated space could not suffice. I'm working on a code where I need a reference to an element in a vector, like: int main(){ vector<int> v; v.push_back(1); int *ptr = &v[0]; for(int i=2; i<100; i++) v.push_back(i); cout << *ptr << endl; //? return 0; } But it's not necessarily true that ptr contains a reference to v[0], right? How would be a good way to guarantee it? My first idea would be to use a vector of pointers and dynamic allocation. I'm wondering if there's an easier way to do that? PS.: Actually I'm using a vector of a class instead of int, but I think the issues are the same.

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  • Template access of symbol in unnamed namespace

    - by Fred Larson
    We are upgrading our XL C/C++ compiler from V8.0 to V10.1 and found some code that is now giving us an error, even though it compiled under V8.0. Here's a minimal example: test.h: #include <iostream> #include <string> template <class T> void f() { std::cout << TEST << std::endl; } test.cpp: #include <string> #include "test.h" namespace { std::string TEST = "test"; } int main() { f<int>(); return 0; } Under V10.1, we get the following error: "test.h", line 7.16: 1540-0274 (S) The name lookup for "TEST" did not find a declaration. "test.cpp", line 6.15: 1540-1303 (I) "std::string TEST" is not visible. "test.h", line 5.6: 1540-0700 (I) The previous message was produced while processing "f<int>()". "test.cpp", line 11.3: 1540-0700 (I) The previous message was produced while processing "main()". We found a similar difference between g++ 3.3.2 and 4.3.2. I also found in g++, if I move the #include "test.h" to be after the unnamed namespace declaration, the compile error goes away. So here's my question: what does the Standard say about this? When a template is instantiated, is that instance considered to be declared at the point where the template itself was declared, or is the standard not that clear on this point? I did some looking though the n2461.pdf draft, but didn't really come up with anything definitive.

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  • Portable way of counting milliseconds in C++ ?

    - by ereOn
    Hi, Is there any portable (Windows & Linux) way of counting how many milliseconds elapsed between two calls ? Basically, I want to achieve the same functionnality than the StopWatch class of .NET. (for those who already used it) In a perfect world, I would have used boost::date_time but that's not an option here due to some silly rules I'm enforced to respect. For those who better read code, this is what I'd like to achieve. Timer timer; timer.start(); // Some instructions here timer.stop(); // Print out the elapsed time std::cout << "Elapsed time: " << timer.milliseconds() << "ms" << std::endl; So, if there is a portable (set of) function(s) that can help me implement the Timer class, what is it ? If there is no such function, what Windows & Linux API should I use to achieve this functionnality ? (using #ifdef WINDOWS-like macros) Thanks !

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  • Can't see anything wrong with simple code

    - by melee
    Here is my implementation file: using namespace std; #include <iostream> #include <iomanip> #include <string> #include <stack> //line 5 #include "proj05.canvas.h" //----------------Constructor----------------// Canvas::Canvas() //line 10 { Title = ""; Nrow = 0; Ncol = 0; image[][]; // line 15 PixelCoordinates.r = 0; PixelCoordinates.c = 0; } //-------------------Paint------------------// line 20 void Canvas::Paint(int R, int C, char Color) { cout << "Paint to be implemented" << endl; } The errors I'm getting are these: proj05.canvas.cpp: In function 'std::istream& operator>>(std::istream&, Canvas&)': proj05.canvas.cpp:11: error: expected `;' before '{' token proj05.canvas.cpp:22: error: a function-definition is not allowed here before '{' token proj05.canvas.cpp:24: error: expected `}' at end of input proj05.canvas.cpp:24: error: expected `}' at end of input These seem like simple syntax errors, but I am not sure what's wrong. Could someone decode these for me? I'd really appreciate it, thanks for your time!

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  • Using pair in c++

    - by user1543957
    Can someone please tell why i am unable to compile the following program #include<iostream> #include<string> #include<cmath> #include<iostream> #include<cfloat> #define MOD 10000009 using namespace std; double distance(pair<int,int> p1,pair<int,int> p2) { double dist; dist = sqrt( (p1.first-p2.first)*(p1.first-p2.first) + (p1.second-p2.second)*(p1.second-p2.second) ); return(dist); } int main() { int N,i,j; cin >> N; pair<int,int> pi[N]; for(i=0;i<N;i++) { cin >> pi[i].first >> pi[i].second; } for(i=0;i<N;i++) { cout << pi[i].first << " "<< pi[i].second << endl; } distance(pi[0],pi[1]); // This line is giving error return 0; }

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  • Binary Search Tree, cannot do traversal

    - by ihm
    Please see BST codes below. It only outputs "5". what did I do wrong? #include <iostream> class bst { public: bst(const int& numb) : root(new node(numb)) {} void insert(const int& numb) { root->insert(new node(numb), root); } void inorder() { root->inorder(root); } private: class node { public: node(const int& numb) : left(NULL), right(NULL) { value = numb; } void insert(node* insertion, node* position) { if (position == NULL) position = insertion; else if (insertion->value > position->value) insert(insertion, position->right); else if (insertion->value < position->value) insert(insertion, position->left); } void inorder(node* tree) { if (tree == NULL) return; inorder(tree->left); std::cout << tree->value << std::endl; inorder(tree->right); } private: node* left; node* right; int value; }; node* root; }; int main() { bst tree(5); tree.insert(4); tree.insert(2); tree.insert(10); tree.insert(14); tree.inorder(); return 0; }

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  • creating a vector with references to some of the elements of another vector

    - by memC
    hi, I have stored instances of class A in a std:vector, vec_A as vec_A.push_back(A(i)). The code is shown below. Now, I want to store references some of the instances of class A (in vec_A) in another vector or another array. For example, if the A.getNumber() returns 4, 7, 2 , I want to put a reference to that instance of A in another vector, say std:vector<A*> filtered_A or an array. Can someone sow me how to do this?? Thanks! class A { public: int getNumber(); A(int val); ~A(){}; private: int num; }; A::A(int val){ num = val; }; int A::getNumber(){ return num; }; int main(){ int i =0; int num; std::vector<A> vec_A; for ( i = 0; i < 10; i++){ vec_A.push_back(A(i)); } std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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  • Finding minimum value in a Map

    - by Sunny
    I have a map and I want to find the minimum value (right hand side) in the map. Right now here is how I did it bool compare(std::pair<std::string ,int> i, pair<std::string, int> j) { return i.second < j.second; } //////////////////////////////////////////////////// std::map<std::string, int> mymap; mymap["key1"] = 50; mymap["key2"] = 20; mymap["key3"] = 100; std::pair<char, int> min = *min_element(mymap.begin(), mymap.end(), compare); std::cout << "min " << min.second<< " " << std::endl; This works fine and I'm able to get the minimum value the problem is when I put this code inside my class it doesn't seem to work int MyClass::getMin(std::map<std::string, int> mymap) { std::pair<std::string, int> min = *min_element(mymap.begin(), mymap.end(), (*this).compare); //error probably due to this return min.second; } bool MyClass::compare( std::pair<std::string, int> i, std::pair<std::string, int> j) { return i.second < j.second; } Also is there a better solution not involving to writing the additional compare function

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  • SHGetFolderPath

    - by user530589
    This code works for windows 7 but doesn't work for windows XP (outputs only part of startup folder path) #include <iostream> #include <shlobj.h> using namespace std; int main() { wchar_t startupFolder[1024]; HRESULT hr = SHGetFolderPath(0, CSIDL_STARTUP, 0, 0, startupFolder); if (SUCCEEDED(hr)) wcout << L"Startup folder = " << startupFolder << endl; else cout << "Error when getting startup folder\n"; getchar(); return 0; } output is: Startup folder = C:\Documents and Settings\Admin\ <- cursor is here. Newline is not provided. Also I have russian window xp. I think this is unicode issue. when I use wprintf I got: C:\Documents and Settings\Admin\???????? ..... Thanks. As a temporary solution: After SHGetFolderPath I call GetShortPathName then I get path in msdos style: C:\DOCUME~1\Admin\5D29~1\4A66~1\60C2~1 Not really beautiful solution, but at least that is a valid path.

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  • What does the destructor do silently?

    - by zhanwu
    Considering the following code which looks like that the destructor doesn't do any real job, valgrind showed me clearly that it has memory leak without using the destructor. Any body can explain me what does the destructor do in this case? #include <iostream> using namespace std; class A { private: int value; A* follower; public: A(int); ~A(); void insert(int); }; A::A(int n) { value = n; follower = NULL; } A::~A() { if (follower != NULL) delete follower; cout << "do nothing!" << endl; } void A::insert(int n) { if (this->follower == NULL) { A* f = new A(n); this->follower = f; } else this->follower->insert(n); } int main(int argc, char* argv[]) { A* objectA = new A(1); int i; for (i = 0; i < 10; i++) objectA->insert(i); delete objectA; }

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  • problem with a string's format in c++ while doing tcp communication

    - by james t
    hi, i am building a simple c++ client, i am splitting the info i get from the server to frames, and pass each frame to a function that processes it, i split the frame into lines using Poco::StringTokenizer tokenizer(frame, "\n"); i take the first line of the tokenizer which represents the type of frame StmpCommand command(tokenizer[0]); a StmpCommand is an enum with the different types of messages and the constructor works as follows : StmpCommand(std::string command): commandType_() { bool x=command=="CONNECTED"; std::cout<<x<<std::endl; if ("SUBSCRIBE" == command) commandType_ = SUBSCRIBE; else if ("UNSUBSCRIBE" == command) commandType_ = UNSUBSCRIBE; else if ("SEND" == command) commandType_ = SEND; else if ("BEGIN" == command) commandType_ = BEGIN; else if ("COMMIT" == command) commandType_ = COMMIT; else if ("CONNECT" == command) commandType_ = CONNECT; else if ("MESSAGE" == command) commandType_ = MESSAGE; else if ("RECEIPT" == command) commandType_ = RECEIPT; else if ("CONNECTED" == command) commandType_ = CONNECTED; else if ("DISCONNECT" == command) commandType_ = DISCONNECT; else if ("ERROR" == command) commandType_ = ERROR; else { std::cerr<<"Error in building StmpCommand object, unknown type - "<<command<<std::endl; } } the first frame i am trying to proccess is a CONNECTED frame therefor i try to create a StmpCommand with CONNECTED as the constructor's only argument and for some reason i am getting an : Error in building StmpCommand object, unknown type - CONNECTED i am clearly passing a string containing CONNECTED but i'm guessing there is something else there that isn't allowing the condition else if ("CONNECTED" == command) to hap

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  • why no implicit conversion from pointer to reference to const pointer.

    - by user316606
    I'll illustrate my question with code: #include <iostream> void PrintInt(const unsigned char*& ptr) { int data = 0; ::memcpy(&data, ptr, sizeof(data)); // advance the pointer reference. ptr += sizeof(data); std::cout << std::hex << data << " " << std::endl; } int main(int, char**) { unsigned char buffer[] = { 0x11, 0x11, 0x11, 0x11, 0x22, 0x22, 0x22, 0x22, }; /* const */ unsigned char* ptr = buffer; PrintInt(ptr); // error C2664: ... PrintInt(ptr); // error C2664: ... return 0; } When I run this code (in VS2008) I get this: error C2664: 'PrintInt' : cannot convert parameter 1 from 'unsigned char *' to 'const unsigned char *&'. If I uncomment the "const" comment it works fine. However shouldn't pointer implicitly convert into const pointer and then reference be taken? Am I wrong in expecting this to work? Thanks!

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  • Acessing a struct member, using a pointer to a vector of structs. Error:base operand of '->' has non-pointer type

    - by Matt Munson
    #include <iostream> #include <vector> using namespace std; struct s_Astruct { vector <int> z; }; int main () { vector <s_Astruct> v_a; for(int q=0;q<10;q++) { v_a.push_back(s_Astruct()); for(int w =0;w<5;w++) v_a[q].z.push_back(8); } vector <s_Astruct> * p_v_a = & v_a; cout << p_v_a[0]->z[4]; //error: base operand of '->' has non-pointer type //'__gnu_debug_def::vector<s_Astruct, std::allocator<s_Astruct> >' } There seems to be some issue with this sort of operation that I don't understand. In the code that I'm working on I actually have things like p_class-vector[]-vector[]-int; and I'm getting a similar error.

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  • multiple calls to realloc() seems to cause a heap corruption..

    - by Windindeed
    What's the problem with this code? It crashes every time. One time it's a failed assertion "_ASSERTE(_CrtIsValidHeapPointer(pUserData));", other times it is just a "heap corrpuption" error. Changing the buffer size affects this issue in some strange ways - sometimes it crashes on the "realloc", and other times on the "free". I have debugged this code many times, and there is nothing abnormal regarding the pointers. char buf[2000]; char *data = (char*)malloc(sizeof(buf)); unsigned int size = sizeof(buf); for (unsigned int i = 0; i < 5; ++i) { char *ptr = data + size; size += sizeof(buf); char *tmp = (char*)realloc(data, size); if (!tmp) { std::cout << "Oh no.."; break; } data = tmp; memcpy(ptr, buf, sizeof(buf)); } free(data); Thanks!

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  • Confusion about pointers and their memory addresses

    - by TimothyTech
    alright, im looking at a code here and the idea is difficult to understand. #include <iostream> using namespace std; class Point { public : int X,Y; Point() : X(0), Y(0) {} }; void MoveUp (Point * p) { p -> Y += 5; } int main() { Point point MoveUp(&point) cout <<point.X << point.Y; return 0; } Alright, so i believe that a class is created and X and Y are declared and they are put inside a constructor a method is created and the argument is Point * p, which means that we are going to stick the constructor's pointer inside the function; now we create an object called point then call our method and put the pointers address inside it? isnt the pointers address just a memory number like 0x255255? and why wasnt p ever declared? (int * p = Y) what is a memory addres exactly? that it can be used as an argument?

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  • (C++) Loading a file into a vector

    - by Alden
    This is probably a simple question, however I am new to C++ and I cannot figure this out. I am trying to load a binary file and load each byte to a vector. This works fine with a small file, but when I try to read larger than 410 bytes the program crashes and says: This application has requested the Runtime to terminate it in an unusual way. Please contact the application's support team for more information. I am using code::blocks on windows. This is the code: #include <iostream> #include <fstream> #include <vector> using namespace std; int main() { std::vector<char> vec; std::ifstream file; file.exceptions( std::ifstream::badbit | std::ifstream::failbit | std::ifstream::eofbit); file.open("file.bin"); file.seekg(0, std::ios::end); std::streampos length(file.tellg()); if (length) { file.seekg(0, std::ios::beg); vec.resize(static_cast<std::size_t>(length)); file.read(&vec.front(), static_cast<std::size_t>(length)); } int firstChar = static_cast<unsigned char>(vec[0]); cout << firstChar <<endl; return 0; } Thank you for your help!

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