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• FFmpeg and qt, Unable to find a suitable output format for '>'

  - by Spredzy

  Hi all, I'm trying to execute a ffmpeg operation through Qt I would like to execute this line : ./ffmpeg -t 10 -i temp1 -f mpeg - > temp2 When I execute through the terminal, it works perfectly fine. How ever when I launch it through Qt like this : QProcess *process = new QProcess(); QString parameters("./ffmpeg -t 10 -i temp1 -f mpeg - > temp2"); std::cout << process->execute(parameters) << std::endl; I get an Unable to find a suitable output format for '>' any body has the idea of why ?

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• How to browse a Matrix returned by the OpenCV2.0 Canny() function ?

  - by user290613

  Hi all, I've been browsing the web to get an answer but no way to put my hand on it. I call the Canny function that fills me a matrix Canny(src, dst, 220, 299, 3 ); the dst variable is now a Matrix that is according to me of type CV_8UC1, 8bit, 1channel. Now I would like to browse this matrix according to rows and columns, so there was a trick that I've seen on stackoverflow dst.at<uchar*>(3, 5) In my case it crashes. (Assertion Failed, unknown function, cxmat.hpp line 450) My matrix information are myMatrix.width() = 181 myMatrix.height() = 65 One more thing, when I do std::cout << dst.depth() << std::endl; It always retrieves me 0 and not 8 (which I guess Im suppose to get) Thank you very much for all who will reply,

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• What are pointers to class members used for?

  - by srikfreak

  I have read about pointers to class members, but I have never seen them being used in any practical applications. Can someone explain what are the use cases of such pointers? Is it really necessary to have such pointers? Eg. class abc { public: int a; abc(int val) { a = val; } }; int main { int abc::*data; abc obj(5); data = &abc::a; cout << "Value of a is " << obj.*data << endl; return 0; } In the above eg. why is the value of 'a' accessed in this manner? What is the advantage of using pointers to class members?

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• STL map inside map C++

  - by Prasanth Madhavan

  In c++ STL map, i have a definition like map<string, map<int, string> >; and i iterate it using the following code. for( map<string, map<int, string> >::iterator ii=info.begin(); ii!=info.end(); ++ii){ for(map<int, string>::iterator j=ii->second.begin(); j!=ii->second.end();++j){ cout << (*ii).first << " : " << (*j).first << " : "<< (*j).second << endl; } } My doubt is is this the correct way to iterate or is there a better way to do so? The above code works for me. But m looking for a more elegant solution.

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• Are large include files like iostream efficient? (C++)

  - by Keand64

  Iostream, when all of the files it includes, the files that those include, and so on and so forth, adds up to about 3000 lines. Consider the hello world program, which needs no more functionality than to print something to the screen: #include <iostream> //+3000 lines right there. int main() { std::cout << "Hello, World!"; return 0; } this should be a very simple piece of code, but iostream adds 3000+ lines to a marginal piece of code. So, are these 3000+ lines of code really needed to simply display a single line to the screen, and if not, do they create a less efficient program than if I simply copied the relevant lines into the code?

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• Implicit casting Integer calculation to float in C++

  - by Ziddiri

  Is there any compiler that has a directive or a parameter to cast integer calculation to float implicitly. For example: float f = (1/3)*5; cout << f; the "f" is "0", because calculation's constants(1, 3, 10) are integer. I want to convert integer calculation with a compiler directive or parameter. I mean, I won't use explicit casting or ".f" prefix like that: float f = ((float)1/3)*5; or float f = (1.0f/3.0f)*5.0f; Do you know any c/c++ compiler which has any parameter to do this process without explicit casting or ".f" thing?

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• Cannot find sleep function

  - by Tyzak

  hello, i'm new at C Programming (i learned c++) i want to create a process with windows.h at first i just want to start my main programm that creates a process ( -- starts an other programm) that's my code, but it doesn't really work, i removed every unnessasery line of code but "void sleep(700)" (or "sleep (700)" for testing if the windows methods work, but i get an error, that "sleep" cant be found. #include <iostream> #include <windows.h> #include <string> using namespace std; void main() { //bool ret; //startupinfo stupinfo; //prozess_information pro2info; //Getstartupinfo (&stupinfo); //createprozess(null, "C:\\bsss10\\betriebssystemePRA1.exe", null, null, false, create_new_console, null, // null, &stupinfo, &pro2info); sleep (700); cout<< "hello"; } thanks in advance

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• How *restrict / *__restrict__ works in C / C++?

  - by Moraru Lilian

  Here is some code I wrote: #include <iostream> using namespace std; int main(void) { int i = 7; int *__restrict__ a = &i; *a = 5; int *b = &i, *c = &i; *b = 8; *c = 9; cout << **&a << endl; //*a return 0; } From what I've read, if I do " *a = 5 ", it changes the value of the memory he, "a", is pointing to, after that the memory to which he is pointing to should not be modified by anyone else except "a", which means that these program is wrong because "b" and "c" modify it after that. Or, even if "b" modifies "i" first, after that only "a" should have access to that memory( "i" ). Am I getting it correctly?

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• VS 11 with std::future - Is this a bug?

  - by cooky451

  I recently installed the Visual Studio 11 Developer Preview. While playing with threads and futures, I came around this setup: #include <future> #include <iostream> int foo(unsigned a, unsigned b) { return 5; } int main() { std::future<int> f = std::async(foo, 5, 7); std::cout << f.get(); } So, very simple. But since there are two arguments for "foo", VS 11 doesn't want to compile it. (However, g++ does: http://ideone.com/ANrPj) (The runtime error is no problem: std::future exception on gcc experimental implementation of C++0x) (VS 11 errormessage: http://pastebin.com/F9Xunh2s) I'm a little confused right now, since this error seems extremely obvious to me, even if it is a developer preview. So my questions are: Is this code correct according to the C++11 standard? Is this bug already known/reported?

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• How can I work around the fact that in C++, sin(3.14159265) is not 0?

  - by Adam Doyle

  In C++, const double Pi = 3.14159265; cout << sin(Pi); // displays: 3.58979e-009 it SHOULD display the number zero I understand this is because Pi is being approximated, but is there any way I can have a value of Pi hardcoded into my program that will return 0 for sin(Pi)? (a different constant maybe?) In case you're wondering what I'm trying to do: I'm converting polar to rectangular, and while there are some printf() tricks I can do to print it as "0.00", it still doesn't consistently return decent values (in some cases I get "-0.00") The lines that require sin and cosine are: x = r*sin(theta); y = r*cos(theta); BTW: My Rectangular - Polar is working fine... it's just the Polar - Rectangular Thanks! edit: I'm looking for a workaround so that I can print sin(some multiple of Pi) as a nice round number to the console (ideally without a thousand if-statements)

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• Invalid conversion from int to int** C++

  - by user69514

  Not sure why I'm getting this error. I have the following: int* arr = new int[25]; int* foo(){ int* i; cout << "Enter an integer:"; cin >> *i; return i; } void test(int** myInt){ *myInt = foo(); } This call here is where I get the error: test(arr[0]); //here i get invalid conversion from int to int**

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• How to detect an overflow in C++ ?

  - by Tim

  Hi, I just wonder if there is some convenient way to detect if overflow happens to any variable of any default data type used in a C++ program during runtime? By convenient, I mean no need to write code to follow each variable if it is in the range of its data type every time its value changes. Or if it is impossible to achieve this, how would you do? For example, float f1=FLT_MAX+1; cout << f1 << endl; doesn't give any error or warning in either compilation with "gcc -W -Wall" or running. Thanks and regards!

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• getline() returns empty line in Eclipse but working properly in Dev C++

  - by pocoa

  Here is my code: #include <iostream> #include <stdlib.h> #include <fstream> using namespace std; int main() { string line; ifstream inputFile; inputFile.open("input.txt"); do { getline(inputFile, line); cout << line << endl; } while (line != "0"); return 0; } input.txt content: 5 9 2 9 3 8 2 8 2 1 0 In Enclipse, it goes to infinite-loop. I'm using MinGW 5.1.6 + Eclipse CDT. I tried many things but I couldn't find the problem.

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• Problem with operator ==

  - by CPPDev

  I am facing some problem with use of operator == in the following c++ program. #include < iostream> using namespace std; class A { public: A(char *b) { a = b; } A(A &c) { a = c.a; } bool operator ==(A &other) { return strcmp(a, other.a); } private: char *a; }; int main() { A obj("test"); A obj1("test1"); if(obj1 == A("test1")) { cout<<"This is true"<<endl; } } What's wrong with if(obj1 == A("test1")) line ?? Any help is appreciated.

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• Copying non null-terminated unsigned char array to std::string

  - by karlphillip

  If the array was null-terminated this would be pretty straight forward: unsigned char u_array[4] = { 'a', 's', 'd', '\0' }; std::string str = reinterpret_cast<char*>(u_array); std::cout << "-> " << str << std::endl; However, I wonder what is the most appropriate way to copy a non null-terminated unsigned char array, like the following: unsigned char u_array[4] = { 'a', 's', 'd', 'f' }; into a std::string. Is there any way to do it without iterating over the unsigned char array? Thank you all.

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• Unsigned long with negative value

  - by egiakoum1984

  Please see the simple code below: #include <iostream> #include <stdlib.h> using namespace std; int main(void) { unsigned long currentTrafficTypeValueDec; long input; input=63; currentTrafficTypeValueDec = (unsigned long) 1LL << input; cout << currentTrafficTypeValueDec << endl; printf("%u \n", currentTrafficTypeValueDec); printf("%ld \n", currentTrafficTypeValueDec); return 0; } Why printf() displays the currentTrafficTypeValueDec (unsigned long) with negative value? The output is: 9223372036854775808 0 -9223372036854775808

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• pointer to member function question

  - by Steve

  Hello, I'm trying to replicate a template I've used before with a member function, and it isn't going very well. The basic form of the function is template<class T> T Convert( HRESULT (*Foo)(T*)) { T temp; Foo(&temp); //Throw if HRESULT is a failure return temp; } HRESULT Converter(UINT* val) { *val = 1; return S_OK; } int _tmain(int argc, _TCHAR* argv[]) { std::cout << Convert<UINT>(Converter) << std::endl; return 0; } For the life of me, I can't get this to work with a member variable. I've read up on their syntax, and I can't seem to figure out how to make it work with templates. The class would be something similar to class TestClass { HRESULT Converter(UINT* val) { *val = 1; return S_OK; } }

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• What does the '&' operator do in C++?

  - by rascher

  n00b question. I am a C guy and I'm trying to understand some C++ code. I have the following function declaration: int foo(const string &myname) { cout << "called foo for: " << myname << endl; return 0; } How does the function signature differ from the equivalent C: int foo(const char *myname) Is there a difference between using string *myname vs string &myname? What is the difference between & in C++ and * in C to indicate pointers? Similarly: const string &GetMethodName() { ... } What is the & doing here? Is there some website that explains how & is used differently in C vs C++?

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• Inheriting and static members

  - by Bruce

  Here is my code - #include <iostream> #include <conio.h> using namespace std; class Base { public: int a; }; //int Base::a = 5; class Derived : public Base { public: int static a; }; int main() { Derived d; cout<<d.a; getch(); return 0; } I get a linker error here. But when I do it the other way round - class Base { public: int static a; }; int Base::a = 5; class Derived : public Base { public: int a; }; I get no error. Can someone please explain what is happening here.

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• Is there a way to make `enum` type to be unsigned?

  - by Kirill V. Lyadvinsky

  Is there a way to make enum type to be unsigned? The following code gives me a warning about signed/unsigned comparison. enum EEE { X1 = 1 }; int main() { size_t x = 2; EEE t = X1; if ( t < x ) std::cout << "ok" << std::endl; return 0; } I've tried to force compiler to use unsigned underlying type for enum with the following: enum EEE { X1 = 1, XN = 18446744073709551615LL }; But that still gives the warning.

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• How do I redirect output from the Visual Studio debugger?

  - by jeatsy

  In Visual Studio 2008, I can specify a message to be printed when a breakpoint is hit (by right-clicking the breakpoint and choosing 'When Hit...'). When the program is run, these messages appear in the Output Window. I would like to know, is there any way to redirect them to a file? Specifying file.txt as a command argument to the program does not work: this redirects the program's output, but not the debugger's. (FWIW the behaviour I wish to achieve is to get the debugger to repeatedly print a variable's value to a file, rather than peppering my code with printf/cout statements.)

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• how to read character from console in c++?

  - by tsubasa

  I'm struggling with reading characters from console in c++. Here is what I tried to do: char x; char y; char z; cout<<"Please enter your string: "; string s; getline(cin,s); istringstream is(s); is>> x >> y >> z; The problem is if the user enter something like this "1 20 100": x will get 1 y will get 2 z will get 0 What I want to get is x = 1; y = 20; z = 100; Anybody has suggestions?

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• Visual c++ opencv 2.1 contains()

  - by kaushalyjain

  how to check whether a given point is contained in a rectangle using the contains() function in Rect_ construct... Please give me the exact function and its parameters.Like when i type this Point b(2,2); Rect a(10,10,50,50); cout<< Rect_::contains(b); There is a compile error saying 1c:\users\kaushal\documents\visual studio 2008\projects\test1\test1.cpp(23) : error C2352: 'cv::Rect_<Tp::contains' : illegal call of non-static member function 1c:\opencv2.1\include\opencv\cxcore.hpp(385) : see declaration of 'cv::Rect<_Tp::contains'

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• Passing Text for command line

  - by Kasun

  Hi, I need to pass some text which is in richtext box to command line. This is my Button click even which start the cmd. private void button1_Click(object sender, EventArgs e) { ProcessStartInfo psi = new ProcessStartInfo { FileName = "cmd", Arguments = @"/k ""C:\Program Files\Microsoft Visual Studio 9.0\VC\bin\vcvars32.bat""", }; Process.Start(psi); } In my rich text box contain following text. include iostream using namespace std; int main() { cout << "Welcome to the wonderful world of C++!!!\n"; return 0; } Can anyone provide me necessary codes.

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• C++ input chaining in C#

  - by Monty

  I am trying to learn C# coming from C++. I am writing just some basic console stuff to get a feel for it and was wondering if it is possible to do simple chaining of inputs in C#. For example in C++: cout<<"Enter two numbers: "; cin >> int1 >> int2; You could then just input 3 5 and hit enter and the values will be fine. In C# however I have to split it up(as far as I can tell) like this: Console.Write("Enter the first number: "; int1 = (char)Console.Read(); Console.Writeline(""); Console.Write("Enter the second number: "; int2 = (char)Console.Read(); Maybe I am just missing something.

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