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  • SQL Server float datatype

    - by Martin Smith
    The documentation for SQL Server Float says Approximate-number data types for use with floating point numeric data. Floating point data is approximate; therefore, not all values in the data type range can be represented exactly. Which is what I expected it to say. If that is the case though why does the following return 'Yes' in SQL Server DECLARE @D float DECLARE @E float set @D = 0.1 set @E = 0.5 IF ((@D + @D + @D + @D +@D) = @E) BEGIN PRINT 'YES' END ELSE BEGIN PRINT 'NO' END but the equivalent C++ program returns "No"? #include <iostream> using namespace std; int main() { float d = 0.1F; float e = 0.5F; if((d+d+d+d+d) == e) { cout << "Yes"; } else { cout << "No"; } }

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  • difference in using virtual and not using virtual

    - by numerical25
    In C++, whether you choose to use virtual or not, you can still override the base class function. The following compiles just fine... class Enemy { public: void SelectAnimation(); void RunAI(); void Interact() { cout<<"Hi I am a regular Enemy"; } private: int m_iHitPoints; }; class Boss : public Enemy { public: void Interact() { cout<<"Hi I am a evil Boss"; } }; So my question is what is the difference in using or not using the virtual function. And what is the disadvantage.

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  • Specify a base classes template parameters while instantiating a derived class?

    - by DaClown
    Hi, I have no idea if the title makes any sense but I can't find the right words to descibe my "problem" in one line. Anyway, here is my problem. There is an interface for a search: template <typename InputType, typename ResultType> class Search { public: virtual void search (InputType) = 0; virtual void getResult(ResultType&) = 0; }; and several derived classes like: template <typename InputType, typename ResultType> class XMLSearch : public Search<InputType, ResultType> { public: void search (InputType) { ... }; void getResult(ResultType&) { ... }; }; The derived classes shall be used in the source code later on. I would like to hold a simple pointer to a Search without specifying the template parameters, then assign a new XMLSearch and thereby define the template parameters of Search and XMLSearch Search *s = new XMLSearch<int, int>(); I found a way that works syntactically like what I'm trying to do, but it seems a bit odd to really use it: template <typename T> class Derived; class Base { public: template <typename T> bool GetValue(T &value) { Derived<T> *castedThis=dynamic_cast<Derived<T>* >(this); if(castedThis) return castedThis->GetValue(value); return false; } virtual void Dummy() {} }; template <typename T> class Derived : public Base { public: Derived<T>() { mValue=17; } bool GetValue(T &value) { value=mValue; return true; } T mValue; }; int main(int argc, char* argv[]) { Base *v=new Derived<int>; int i=0; if(!v->GetValue(i)) std::cout<<"Wrong type int."<<std::endl; float f=0.0; if(!v->GetValue(f)) std::cout<<"Wrong type float."<<std::endl; std::cout<<i<<std::endl<<f; char c; std::cin>>c; return 0; } Is there a better way to accomplish this?

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  • Vim syntax/compile-time error highlighting

    - by Tim Nordenfur
    Is there a Vim script that periodically tries to compile/interpret the code that I'm working on, and highlights syntax errors? I'd like it to point out that something is wrong between these lines: int a = 42 cout << a << endl; Such a thing would save me loads of time. I'm primarily searching for a Perl-syntax checker, but I'd also be interested in similar plugins for other languages. Update: Another error I'd like it to point out: int a == 42; cout << a << endl;

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  • Passing an array of an array of char to a function

    - by L.A. Rabida
    In my program, I may need to load a large file, but not always. So I have defined: char** largefilecontents; string fileName="large.txt"; When I need to load the file, the program calles this function: bool isitok=LoadLargeFile(fileName,largefilecontents); And the function is: bool LoadLargeFile(string &filename, char ** &lines) { if (lines) delete [] lines; ifstream largeFile; #ifdef LINUX largeFile.open(filename.c_str()); #endif #ifdef WINDOWS largeFile.open(filename.c_str(),ios::binary); #endif if (!largeFile.is_open()) return false; lines=new char *[10000]; if (!lines) return false; largeFile.clear(); largeFile.seekg(ios::beg); for (int i=0; i>-1; i++) { string line=""; getline(largeFile,line); if (largeFile.tellg()==-1) break; //when end of file is reached, tellg returns -1 lines[i]=new char[line.length()]; lines[i]=const_cast<char*>(line.c_str()); cout << lines[i] << endl; //debug output } return true; } When I view the debug output of this function, "cout << lines[i] << endl;", it is fine. But when I then check this in the main program like this, it is all messed up: for (i=0; i<10000; i++) cout << largefilecontents[i] << endl; So within the function LoadLargeFile(), the results are fine, but without LoadLargeFile(), the results are all messed up. My guess is that the char ** &lines part of the function isn't right, but I do not know what this should be. Could someone help me? Thank you in advance!

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  • Talking to a server in Win32; how do I see the server's response?

    - by Vinod K
    I am new to Win32 programming. sprintf(lpszBuff,"HELO Mail-Server\r\n"); send(s,lpszBuff,strlen(lpszBuff),0); recv(s,lpszBuff,100,0); cout << lpszBuff; In here I connect to a local mail server. The buffer contains the request I send, the same buffer contains the reply send by the browser. How do I see the reply? cout <<buffer doesn't show any output. I am doing this on VC++ 2008.

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  • How to Replace only Part of the Variable using #define

    - by mahesh
    #define C_TX_ TX_ #define C_RX_ RX_ enum Test { C_TX_MAC 0x0100, // Pre-Processor should replace C_TX_ to TX_ C_RX_MAC 0x0101 // But Not Working. }; int main(int argc, char *argv[]) { cout << TX_MAC; // HOW TO PRINT ? cout << RX_MAC; // HOW TO PRINT ? return true; } Please Help. Thanks in Advance

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  • which is time consuming construct in following program?

    - by user388338
    while submitting a solution for practise problem 6(odd) i got TLE error but while using using print and scanf in place cin and cout my sol was submitted successfully with 0.77s time..i want to know how can i make it more efficient link to problem is codechef problem 6 #include<iostream> #include<cstdio> using namespace std; int main() {int n,N; scanf("%d",&n); for(int l=0;l<n;l++) { scanf("%d",&N); int i=0,x; if(N<=0) continue; for(;N>=(x=(2<<i));i++); printf("%d",x/2); cout<<"\n"; } }

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  • Does template class/function specialization improves compilation/linker speed?

    - by Stormenet
    Suppose the following template class is heavily used in a project with mostly int as typename and linker speed is noticeably slower since the introduction of this class. template <typename T> class MyClass { void Print() { std::cout << m_tValue << std::endl;; } T m_tValue; } Will defining a class specialization benefit compilation speed? eg. void MyClass<int>::Print() { std::cout << m_tValue << std::endl; }

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  • c++: how can i read a file line by line to a string type variable?

    - by ufk
    Hiya. I'm trying to read a file line by line to a string type variable using the following code: #include <iostream> #include <fstream> ifstream file(file_name); if (!file) { cout << "unable to open file"; exit(1); } string line; while (!file.eof()) { file.getline(line,256); cout<<line; } file.close(); it won't compile when I try to use String class, only when i use char file[256] instead. how can I get line by line into a string class? thanks!

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  • Returning the address of local or temporary variable

    - by Dave18
    #include <iostream> int& foo() { int i = 6; std::cout << &i << std::endl; return i; } int main() { int i = foo(); std::cout << &i << std::endl; } I know it doesn't return the address of local variable so that is why the warning but why does it still works and assign the variable i in main() to '6'? How does it only return the value if the variable the was removed from stack memory?

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  • strftimedoesnt display year correctly

    - by paultop6
    Hi guys, i have the following code below: const char* timeformat = "%Y-%m-%d %H:%M:%S"; const int timelength = 20; char timecstring[timelength]; strftime(timecstring, timelength, timeformat, currentstruct); cout << "timecstring is: " << timecstring << "\n"; currentstruct is a tm*. The cout is giving me the date in the correct format, but the year is not 2010, but 3910. I know there is something to do with the year cound starting at 1900, but im not sure how to get strftime to recognise this and not add 1900 to the value of 2010 that is there, can anyone help. Regards Paul

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  • C++ converting hexadecimal md5 hash to decimal integer

    - by Zackery
    I'm doing Elgamal Signature Scheme and I need to use the decimal hash value from the message to compute S for signature generation. string hash = md5(message); cout << hash << endl; NTL::ZZ msgHash = strtol(hash.c_str(), NULL, 16); cout << msgHash << endl; There are no integer large enough to contain the value of 32 byte hexadecimal hash, and so I tried big integer from NTL library but it didn't work out because you cannot assign long integer to NTL::ZZ type. Is there any good solution to this? I'm doing this with visual C++ in Visual Studio 2013.

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  • C++: Why does gcc prefer non-const over const when accessing operator[]?

    - by JonasW
    This question might be more appropriately asked regarding C++ in general, but as I am using gcc on linux that's the context. Consider the following program: #include <iostream> #include <map> #include <string> using namespace std; template <typename TKey, typename TValue> class Dictionary{ public: map<TKey, TValue> internal; TValue & operator[](TKey const & key) { cout << "operator[] with key " << key << " called " << endl; return internal[key]; } TValue const & operator[](TKey const & key) const { cout << "operator[] const with key " << key << " called " << endl; return internal.at(key); } }; int main(int argc, char* argv[]) { Dictionary<string, string> dict; dict["1"] = "one"; cout << "first one: " << dict["1"] << endl; return 0; } When executing the program, the output is: operator[] with key 1 called operator[] with key 1 called first one: one What I would like is to have the compiler choose the operator[]const method instead in the second call. The reason is that without having used dict["1"] before, the call to operator[] causes the internal map to create the data that does not exist, even if the only thing I wanted was to do some debugging output, which of course is a fatal application error. The behaviour I am looking for would be something like the C# index operator which has a get and a set operation and where you could throw an exception if the getter tries to access something that doesn't exist: class MyDictionary<TKey, TVal> { private Dictionary<TKey, TVal> dict = new Dictionary<TKey, TVal>(); public TVal this[TKey idx] { get { if(!dict.ContainsKey(idx)) throw KeyNotFoundException("..."); return dict[idx]; } set { dict[idx] = value; } } } Thus, I wonder why the gcc prefers the non-const call over the const call when non-const access is not required.

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  • [C++] Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • Why does this code crash?

    - by user146780
    The following code causes a stack overflow but I don't see why... int _tmain(int argc, _TCHAR* argv[]) { cout << "start"; char bmp[1024][768][3]; for (int p = 0; p < 9000; ++p) { for(int i = 0; i < 1024; ++i) { for(int j = 0; j < 768; ++j) { bmp[i][j][0] = 20; } } } cout << "Stop"; return 0; } Thanks

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  • iPhone/iPad fatal error in C++ code produces no output in the log

    - by morgancodes
    I'm trying to move away from Objective-C to C++ for audio in my iPad programming, due to the a few reports I've heard of Objective-C selectors sometimes causing audio glitches. So I'm starting to use pure C++ files. When a fatal error happens in one of the C++ files, I get no output from the log. The app just crashes. For example, if I do this in my C++ file: env = new ADSR(); cout << "setting env to null\n"; env = NULL; env->setSustainLevel(1); cout << "called function on non-initialized env\n"; I get the following output: setting env to null After that, there's a method called on NULL, which apparently kills the app, but absolutely nothing to that effect is reported. What do I need to do to have useful information logged when there's an error in my C++ code?

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  • [C++] std::tring manipulation: whitespace, "newline escapes '\'" and comments #

    - by rubenvb
    Kind of looking for affirmation here. I have some hand-written code, which I'm not shy to say I'm proud of, which reads a file, removes leading whitespace, processes newline escapes '\' and removes comments starting with #. It also removes all empty lines (also whitespace-only ones). Any thoughts/recommendations? I could probably replace some std::cout's with std::runtime_errors... but that's not a priority here :) const int RecipeReader::readRecipe() { ifstream is_recipe(s_buffer.c_str()); if (!is_recipe) cout << "unable to open file" << endl; while (getline(is_recipe, s_buffer)) { // whitespace+comment removeLeadingWhitespace(s_buffer); processComment(s_buffer); // newline escapes + append all subsequent lines with '\' processNewlineEscapes(s_buffer, is_recipe); // store the real text line if (!s_buffer.empty()) v_s_recipe.push_back(s_buffer); s_buffer.clear(); } is_recipe.close(); return 0; } void RecipeReader::processNewlineEscapes(string &s_string, ifstream &is_stream) { string s_temp; size_t sz_index = s_string.find_first_of("\\"); while (sz_index <= s_string.length()) { if (getline(is_stream,s_temp)) { removeLeadingWhitespace(s_temp); processComment(s_temp); s_string = s_string.substr(0,sz_index-1) + " " + s_temp; } else cout << "Error: newline escape '\' found at EOF" << endl; sz_index = s_string.find_first_of("\\"); } } void RecipeReader::processComment(string &s_string) { size_t sz_index = s_string.find_first_of("#"); s_string = s_string.substr(0,sz_index); } void RecipeReader::removeLeadingWhitespace(string &s_string) { const size_t sz_length = s_string.size(); size_t sz_index = s_string.find_first_not_of(" \t"); if (sz_index <= sz_length) s_string = s_string.substr(sz_index); else if ((sz_index > sz_length) && (sz_length != 0)) // "empty" lines with only whitespace s_string.clear(); } Some extra info: std::string s_buffer is a class data member, so is std::vector v_s_recipe. Any comment is welcome :)

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  • Is there a 'catch' with FastFormat?

    - by Roddy
    I just read about the FastFormat C++ i/o formatting library, and it seems too good to be true: Faster even than printf, typesafe, and with what I consider a pleasing interface: // prints: "This formats the remaining arguments based on their order - in this case we put 1 before zero, followed by 1 again" fastformat::fmt(std::cout, "This formats the remaining arguments based on their order - in this case we put {1} before {0}, followed by {1} again", "zero", 1); // prints: "This writes each argument in the order, so first zero followed by 1" fastformat::write(std::cout, "This writes each argument in the order, so first ", "zero", " followed by ", 1); This looks almost too good to be true. Is there a catch? Have you had good, bad or indifferent experiences with it? CW on this question, as there's probably no right answer...

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  • Access variable value using string representing variable's name

    - by Paul Ridgway
    Hello everyone, If the title was not clear, I will try to clarify what I am asking: Imagine I have a variable called counter, I know I can see its current value by doing something like: std::cout << counter << std::endl; However, assume I have lots of variables and I don't know which I'm going to want to look at until runtime. Does anyone know a way I can fetch the value of a variable by using its name, for example: std::cout << valueOf("counter") << std::endl; I feel being able to do this might make debugging large complex projects easier. Thanks in advance for your time.

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  • how to get stl map to construct/destruct inserted object only once.

    - by Alberto Toglia
    I have found a very prejudicial fact about stl maps. For some reason I cant get objects being inserted in the map to get constructed/destructed only once. Example: struct MyObject{ MyObject(){ cout << "constructor" << endl; } ~MyObject(){ cout << "destructor" << endl; } }; int main() { std::map<int, MyObject> myObjectsMap; myObjectsMap[0] = MyObject(); return 0; } returns: constructor destructor destructor constructor destructor If I do: typedef std::pair<int, MyObject> MyObjectPair; myObjectsMap.insert( MyObjectPair(0,MyObject())); returns: constructor destructor destructor destructor I'm inserting Objects responsible for their own memory allocation, so when destructed they'll clean themselves up, being destructed several times is causing me some trouble.

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  • typeid() returns extra characters in g++

    - by Appu
    class foo { public: void say_type_name() { std::cout << typeid(this).name() << std::endl; } }; int main() { foo f;; f.say_type_name(); } Above code prints P3foo on my ubuntu machine with g++. I am not getting why it is printing P3foo instead of just foo. If I change the code like std::cout << typeid(*this).name() << std::endl; it prints 3foo. Any thoughts?

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  • Question on Virtual Methods

    - by bobber205
    IF both methods are declared as virtual, shouldn't both instances of Method1() that are called be the derived class's Method1()? I am seeing BASE then DERIVED called each time. I am doing some review for an interview and I want to make sure I have this straight. xD class BaseClass { public: virtual void Method1() { cout << "Method 1 BASE" << endl; } }; class DerClass: public BaseClass { public: virtual void Method1() { cout << "Method 1 DERVIED" << endl; } }; DerClass myClass; ((BaseClass)myClass).Method1(); myClass.Method1(); Method 1 BASE Method 1 DERVIED

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  • Convert a number from string to integer without using inbuilt function

    - by Raja
    I am trying this technique but error is coming. Please help me to convert a number from string to integer. #include<iostream> using namespace std; int main() { char *buffer[80]; int a; cout<<"enter the number"; cin.get(buffer,79); char *ptr[80] = &buffer; while(*ptr!='\0') { a=(a*10)+(*ptr-48); } cout<<"the value"<<a; delete ptr[]; return 0; } Errors are: error C2440: 'initializing' : cannot convert from 'char ()[80]' to 'char *[80]' error C2440: '=' : cannot convert from 'char *' to 'int'

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  • sigwait in Linux (Fedora 13) vs OS X

    - by Silas
    So I'm trying to create a signal handler using pthreads which works on both OS X and Linux. The code below works on OS X but doesn't work on Fedora 13. The application is fairly simple. It spawns a pthread, registers SIGHUP and waits for a signal. After spawning the signal handler I block SIGHUP in the main thread so the signal should only be sent to the signal_handler thread. On OS X this works fine, if I compile, run and send SIGHUP to the process it prints "Got SIGHUP". On Linux it just kills the process (and prints Hangup). If I comment out the signal_handler pthread_create the application doesn't die. I know the application gets to the sigwait and blocks but instead of return the signal code it just kills the application. I ran the test using the following commands: g++ test.cc -lpthread -o test ./test & PID="$!" sleep 1 kill -1 "$PID" test.cc #include <pthread.h> #include <signal.h> #include <iostream> using namespace std; void *signal_handler(void *arg) { int sig; sigset_t set; sigemptyset(&set); sigaddset(&set, SIGHUP); while (true) { cout << "Wait for signal" << endl; sigwait(&set, &sig); if (sig == SIGHUP) { cout << "Got SIGHUP" << endl; } } } int main() { pthread_t handler; sigset_t set; // Create signal handler pthread_create(&handler, NULL, signal_handler, NULL); // Ignore SIGHUP in main thread sigfillset(&set); sigaddset(&set, SIGHUP); pthread_sigmask(SIG_BLOCK, &set, NULL); for (int i = 1; i < 5; i++) { cout << "Sleeping..." << endl; sleep(1); } pthread_join(handler, NULL); return 0; }

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