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  • why does this code crash?

    - by ashish yadav
    why does this code crash? is using strcat illegal on character pointers? #include <stdio.h> #include <string.h> int main() { char *s1 = "Hello, "; char *s2 = "world!"; char *s3 = strcat(s1, s2); printf("%s",s3); return 0; } please give a proper way with referring to both array and pointers.

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  • Sort CMap Key by String Length

    - by Yan Cheng CHEOK
    Previously, I am using STL map to perform the mentioned task. struct ltstr { bool operator()(std::string s1, std::string s2) const { const int l1 = s1.length(); const int l2 = s2.length(); if (l1 == l2) { // In alphabetical order. return s1.compare(s2) < 0; } // From longest length to shortest length. return l1 > l2; } }; std::map<std::string, int, ltstr> m; How can I perform the same task using CMap? // How to make key sorted by string length? CMap<CString, LPCTSTR, int, int> m;

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  • "Data type mismatch in criteria expression"

    - by simon
    Hey guys ! I have a problem when i want to insert values from textboxes to my access database ! When i want to save i get that error ("Data type mismatch in criteria expression") The code: string conString = "Provider=Microsoft.Jet.OLEDB.4.0;" + "Data Source=C:\Users\Simon\Desktop\test5\test5\test5\save.mdb"; OleDbConnection empConnection = new OleDbConnection(conString); string insertStatement = "INSERT INTO aktivnosti_save " + "([ID_uporabnika],[ID_aktivnosti],[kalorij]) " + "VALUES (@ID_uporabnika,@ID_aktivnosti,@kalorij)"; OleDbCommand insertCommand = new OleDbCommand(insertStatement, empConnection); insertCommand.Parameters.Add("@ID_uporabnika", OleDbType.Char).Value = textBox3.Text; insertCommand.Parameters.Add("@ID_zivila", OleDbType.Char).Value = iDTextBox.Text; insertCommand.Parameters.Add("@kalorij", OleDbType.Char).Value = textBox2.Text; empConnection.Open(); try { int count = insertCommand.ExecuteNonQuery(); } catch (OleDbException ex) { MessageBox.Show(ex.Message); } finally { empConnection.Close(); textBox1.Clear(); textBox2.Clear(); } }

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  • Data Types and Structs

    - by dubya
    I'm reviewing for a test, and I am stumped by this question. Consider the following declarations: enum CategoryType {HUMANITIES, SOCIALSCIENCE, NATURALSCIENCE}; const int NUMCOURSES = 100; struct CourseRec { string courseName; int courseNum; CategoryType courseCategory; }; typedef CourseRec CourseList [NUMCOURSES]; CourseList courses; int index1, index2; What is the data type of the expression courses[index1] .courseName[index2] ? (a) CourseList (b) CourseRec (c) string (d) char (e) none; the expression is syntactically invalid I thought that the answer would be string, since courseName is a string, or maybe even CourseRec, since it is in the struct, but the answer is (d)char. Why is this a char data type? Any help is greatly appreciated.

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  • How to find item selected from customContextMenuRequested() on QTreeView item?

    - by vinaym
    I have implemented contextual menus in QTreeView items with the following code MyDerivedQTreeView->setModel(MyDerivedQAbstractItemModel); MyDerivedQTreeView->setContextMenuPolicy(Qt::CustomContextMenu); connect(MyDerivedQTreeView, SIGNAL(customContextMenuRequested(const QPoint &)), MyDerivedQAbstractItemModel(), SLOT(contextualMenu(const QPoint &))); void MyDerivedQAbstractItemModel::contextualMenu(const QPoint& point) { QMenu *menu = new QMenu; menu->addAction(QString("Test Item"), this, SLOT(test_slot())); menu->exec(MyDerivedQTreeView->mapToGlobal(point)); } MyDerivedQAbstractItemModel::contextualMenu() gets called and I can see the contextual menu. Problem is contextual menu should be visible only if user right-clicks on an item and it should be customized as per the item selected. How do I get whether/which item is selected from QPoint information? I am on Qt 4.5.3.

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  • Default values on arguments in C functions and function overloading in C

    - by inquam
    Converting a C++ lib to ANSI C and it seems like though ANSI C doesn't support default values for function variables or am I mistaken? What I want is something like int funcName(int foo, bar* = NULL); Also, is function overloading possible in ANSI C? Would need const char* foo_property(foo_t* /* this */, int /* property_number*/); const char* foo_property(foo_t* /* this */, const char* /* key */, int /* iter */); Could of course just name them differently but being used to C++ I kinda used to function overloading.

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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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  • What causes my borderless C++ app to crash when overriding WndProc?

    - by Ste
    I use a form with border NONE. I need to override WndProc for resize and move form. However, using this code, my app crashes! static const int WM_NCHITTEST = 0x0084; static const int HTCLIENT = 1; static const int HTCAPTION = 2; protected: virtual void Form1::WndProc(System::Windows::Forms::Message %m) override { switch (m.Msg) { case WM_NCHITTEST: if (m.Result == IntPtr(HTCLIENT)) { m.Result = IntPtr(HTCAPTION); } break; } Form1::WndProc(m); } virtual System::Windows::Forms::CreateParams^ get() override { System::Windows::Forms::CreateParams^ cp = __super::CreateParams; cp->Style |= 0x40000; return cp; } How can I fix my code not to crash but still allow my form to be moved and resized?

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  • what does this code do?

    - by bstullkid
    It looks like this just sends a ping, but whats the point of that when you can just use ping? int main (int argc, char *argv[]) { unsigned int pid = 0; char buffer[2]; char *args[] = { "/bin/ping", "-c", "5", NULL, NULL }; if (argc != 2) return 0; args[3] = strdup(argv[1]); for (;;) { gets(buffer); /* FTW */ if (buffer[0] == 0x6e) break; switch (pid = fork()) { case -1: printf("Error Forking\n"); exit(255); case 0: execvp(args[0], args); exit(1); default: break; } } return 255; }

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  • Illegal token on right side of ::

    - by Adam Haile
    I have the following template declaration: template <typename T> void IterTable(int& rIdx, std::vector<double>& rVarVector, const std::vector<T>& aTable, const T aValue, T aLowerBound = -(std::numeric_limits<T>::max()), //illegal token on right side of '::' shows here bool aLeftOpen = true) const; Which throws the illegal token error as noted, on the line with "-(std::numeric_limits::max())". I got this code from some old linux source that I'm trying to compile on Windows. Any idea what the issue is?

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  • return by reference - which of the two is the correct one

    - by eriks
    i have the function: const A& f(...) {...} a. const A a1 = f(..); b. const A &a2 = f(...); which of the is the better one to use? in both cases, if i understand correctly, i prevent the possibility of modifying the returned object. in the first option, the copy constructor of A will be called - am i correct?

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  • Implementing callback functions in C

    - by robertjohn123
    Hi, I am a newbie to C.I am trying to implement callback function using function pointers. I am getting an error :test_callback.c:10: error: expected identifier or ‘(’ before ‘void’ when I try to compile the following program: #include<stdio.h> void (*callback) (void); void callback_proc () { printf ("Inside callback funtion\n"); } void register ((void (*callback) (void))) { printf ("Inside registration \n"); callback (); /* Calling an initial callback with function pointer */ } int main () { callback = callback_proc;/* Assigning function to the function pointer */ register (callback);/* Passing the function pointer */ return 0; } What is this error?Can anyone help?

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  • string manipulation without alloc mem in c

    - by Mike
    I'm wondering if there is another way of getting a sub string without allocating memory. To be more specific, I have a string as: const char *str = "9|0\" 940 Hello"; Currently I'm getting the 940, which is the sub-string I want as, char *a = strstr(str,"9|0\" "); char *b = substr(a+5, 0, 3); // gives me the 940 Where substr is my sub string procedure. The thing is that I don't want to allocate memory for this by calling the sub string procedure. Is there a much easier way?, perhaps by doing some string manipulation and not alloc mem. I'll appreciate any feedback.

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  • C++ iostream not setting eof bit even if gcount returns 0

    - by raph.amiard
    Hi I'm developping an application under windows, and i'm using fstreams to read and write to the file. I'm writing with fstream opened like this : fs.open(this->filename.c_str(), std::ios::in|std::ios::out|std::ios::binary); and writing with this command fs.write(reinterpret_cast<char*>(&e.element), sizeof(T)); closing the file after each write with fs.close() Reading with ifstream opened like this : is.open(filename, std::ios::in); and reading with this command : is.read(reinterpret_cast<char*>(&e.element), sizeof(T)); The write is going fine. However, i read in a loop this way : while(!is.eof()) { is.read(reinterpret_cast<char*>(&e.element), sizeof(T)); } and the program keeps reading, even though the end of file should be reached. istellg pos is 0, and gcount is equal to 0 too, but the fail bit and eof bit are both ok. I'm running crazy over this, need some help ...

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  • Why does it NOT give a segmentation violation?

    - by user198729
    The code below is said to give a segmentation violation: #include <stdio.h> #include <string.h> void function(char *str) { char buffer[16]; strcpy(buffer,str); } int main() { char large_string[256]; int i; for( i = 0; i < 255; i++) large_string[i] = 'A'; function(large_string); return 1; } It's compiled and run like this: gcc -Wall -Wextra hw.cpp && a.exe But there is nothing output. NOTE The above code indeed overwrites the ret address and so on if you really understand what's going underneath.

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  • changing command line arguments

    - by Shadi
    Hi, I am writing a C program. It takes its arguments from commandLine. I want to change the commandLine arguments in the code. As they are defined as "const char *", I can not change them using "strcpy", "memcpy", ... Also, you know, I can not just change their type from "const char *" to "char *". Is there any way to change them? Thank you so much in advance. Best regards, Shadi.

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  • Are indivisible operations still indivisible on multiprocessor and multicore systems?

    - by Steve314
    As per the title, plus what are the limitations and gotchas. For example, on x86 processors, alignment for most data types is optional - an optimisation rather than a requirement. That means that a pointer may be stored at an unaligned address, which in turn means that pointer might be split over a cache page boundary. Obviously this could be done if you work hard enough on any processor (picking out particular bytes etc), but not in a way where you'd still expect the write operation to be indivisible. I seriously doubt that a multicore processor can ensure that other cores can guarantee a consistent all-before or all-after view of a written pointer in this unaligned-write-crossing-a-page-boundary situation. Am I right? And are there any similar gotchas I haven't thought of?

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  • Declaring a C function to return an array

    - by Jaska
    How can I make a function which returns an array? I tried this const int WIDTH=11; const int HEIGHT=11; int main() { char A[WIDTH][HEIGHT]; A=rand_grid(WIDTH,HEIGHT); return 0; } // Initializes a random board. char[][] rand_grid(int i, int k) { char* A[i][k]; for(j=0;j<i;++j) { for(l=0;l<k;++l) { A[j][l]=ran(10); } } return A; } // Returns a random number from the set {0,...,9}. int ran(int i) { srand((unsigned int) time(0)); return(rand()%10); }

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  • Quick strlen question

    - by LearningC
    Hi again. I've come to bother you all with another probably really simple C question. Using the following code: int get_len(char *string){ printf("len: %lu\n", strlen(string)); return 0; } int main(){ char *x = "test"; char y[4] = {'t','e','s','t'}; get_len(x); // len: 4 get_len(y); // len: 6 return 0; } 2 questions. Why are they different and why is y 6? Thanks guys.

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  • Reading in 4 bytes at a time

    - by alphomega
    I have a big file full of integers that I'm loading in. I've just started using C++, and I'm trying out the filestream stuff. From everything I've read, it appears I can only read in bytes, So I've had to set up a char array, and then cast it as a int pointer. Is there a way I can read in 4 bytes at a time, and eliminate the need for the char array? const int HRSIZE = 129951336; //The size of the table char bhr[HRSIZE]; //The table int *dwhr; int main() { ifstream fstr; /* load the handranks.dat file */ std::cout << "Loading table.dat...\n"; fstr.open("table.dat"); fstr.read(bhr, HRSIZE); fstr.close(); dwhr = (int *) bhr; }

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  • Type problem when including tuple

    - by Person
    I'm using Visual Studio 2008 with Feature Pack 1. I have a typedef like this typedef std::tr1::tuple<std::string, std::string, int> tileInfo with a function like this const tileInfo& GetTile( int x, int y ) const. In the implementation file the function has the exact same signature (with the added class name qualifier) and I am getting a redefinition: different type modifiers error. It seems to be looking for an int& instead of a tileInfo& When I mouse over the type of the function in the header, i.e. tileInfo& it brings up a little bar saying static const int tileInfo. I think this may be the problem, but I'm not sure what to do. Any help is appreciated, thanks.

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  • C++ overloading virtual = operator

    - by taz
    Hello, here is the code for my question: class ICommon { public: virtual ICommon& operator=(const ICommon & p)const=0; }; class CSpecial : public ICommon { public: CSpecial& operator=(const CSpecial & cs) { //custom operations return *this; } }; CSpecial obj; Basically: I want the interface ICommon to force it's descendants to implement = operator but don't want to have any typecasts in the implementation. The compiler says "can't instantiate an abstract class. Any help/advice will be appreciated.

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  • java: speed up reading foreign characters

    - by Yang
    My current code needs to read foreign characters from the web, currently my solution works but it is very slow, since it read char by char using InputStreamReader. Is there anyway to speed it up and also get the job done? // Pull content stream from response HttpEntity entity = response.getEntity(); InputStream inputStream = entity.getContent(); StringBuilder contents = new StringBuilder(); int ch; InputStreamReader isr = new InputStreamReader(inputStream, "gb2312"); // FileInputStream file = new InputStream(is); while( (ch = isr.read()) != -1) contents.append((char)ch); String encode = isr.getEncoding(); return contents.toString();

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  • How to debug/reformat C printf calls with lots of arguments in vim?

    - by Costi
    I have a function call in a program that I'm maintaining has 28 arguments for a printf call. It's printing a lot of data in a CSV file. I have problems following finding where what goes and I have some mismatches in the parameters types. I enabled -Wall in gcc and I get warnings like: n.c:495: warning: int format, pointer arg (arg 15) n.c:495: warning: format argument is not a pointer (arg 16) n.c:495: warning: double format, pointer arg (arg 23) The function is like this: fprintf (ConvFilePtr, "\"FORMAT3\"%s%04d%s%04d%s%s%s%d%s%c%s%d%c%s%s%s%s%s%s%s%11.lf%s%11.lf%s%11.lf%s%d\n", some_28_arguments_go_here); I would like to know if there is a vim plugin that highlights the printf format specifier when i go with the cursor over a variable. Other solutions? How to better reformat the code to make it more readable?

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