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• Foo f = Foo(); // no matching function for call to 'Foo::Foo(Foo)' ... huh?!

  - by Kyle

  class Foo { public: explicit Foo() {} explicit Foo(Foo&) {} }; Foo d = Foo(); error: no matching function for call to 'Foo::Foo(Foo)' I tried changing Foo(Foo&) to Foo(Foo) as the error suggests, which AFAIK is not a valid constructor, and sure enough I get: error: invalid constructor; you probably meant ‘Foo (const Foo&)’ What gives? How do I resolve this? (This is on GCC by the way)

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• How to 'hide' spurious "declared but never used" warnings?

  - by Roddy

  I'm using the C++Builder compiler which has a minor bug that certain static const items from system header files can cause spurious "xyzzy is declared but never used" warnings. I'm trying to get my code 100% warning free, so want a way of masking these particular warnings (note - but not by simply turning off the warning!) Also, I can't modify the header files. I need a way of 'faking' the use of the items, preferably without even knowing their type. As an example, adding this function to my .cpp modules fixes warnings for these four items, but it seems a bit 'ad-hoc'. Is there a better and preferably self-documenting way of doing this? static int fakeUse() { return OneHour + OneMinute + OneSecond + OneMillisecond; }

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• Multiplying complex with constant in C++

  - by Atilla Filiz

  The following code fails to compile #include <iostream> #include <cmath> #include <complex> using namespace std; int main(void) { const double b=3; complex <double> i(0, 1), comp; comp = b*i; comp=3*i; return 0; } with error: no match for ‘operator*’ in ‘3 * i’ What is wrong here, why cannot I multiply with immediate constants?

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• Multiple constructors definitions with same name but different signatures (C++)

  - by PuRe_ChAoS12

  With the following code, I keep getting error C2535 when I compile. It's complaining that a member function already defined or declared. Rationnel.h ... class Rationnel { public: Rationnel(int); //Constructor Rationnel(int,int); //Constructor void add(const Rationnel); ... Rationnel.cpp ... //Constructor Rationnel::Rationnel(int n = 1) { numerateur = n; denominateur = 1; } //Constructor Rationnel::Rationnel(int n = 1, int d = 1) { numerateur = n; denominateur = d; } ... Any idea what could be causing the error? Thanks for your time.

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• how to copy char * into a string and visa versa

  - by user295030

  If i pass a char * into a function. I want to then take that char * convert it to a std::string and once I get my result convert it back to char * from a std::string to show the result. I don't know how to do this for conversion ( I am not talking const char * but just char *) I am not sure how to manipulate the value of the pointer I send in. so steps i need to do take in a char * convert it into a string. take the result of that string and put it back in the form of a char * return the result such that the value should be available outside the function and not get destroyed. If possible can i see how it could be done via reference vs a pointer (whose address I pass in by value however I can still modify the value that pointer is pointing to. so even though the copy of the pointer address in the function gets destroyed i still see the changed value outside. thanks!

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• Why does SQLite not bring back any results from my database

  - by tigermain

  This is my first SQLite based iPhone app and I am trying to get it to read a menu hierarchy from my database. The database appears to be registered fine as the compiled statement doesnt error (tried putting in valid table name to test) but for some reason sqlite3_step(compiledStmt) doesnt ever equal SQLITE_ROW as if to suggest there is no data in there; which there is. sqlite3 *database; menu = [[NSMutableArray alloc] init]; if (sqlite3_open([databasePath UTF8String], &database) == SQLITE_OK) { const char *sqlStmt = "SELECT * FROM Menu"; sqlite3_stmt *compiledStmt; if (sqlite3_prepare_v2(database, sqlStmt, -1, &compiledStmt, NULL) == SQLITE_OK) { while (sqlite3_step(compiledStmt) == SQLITE_ROW) { NSString *aTitle = [NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStmt, 1)]; MenuItem *menuItem = [[MenuItem alloc] init]; menuItem.title = aTitle; [menu addObject:menuItem]; [menuItem release]; } } else { NSLog(@"There is an error with the SQL Statement"); } sqlite3_finalize(compiledStmt); } sqlite3_close(database);

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• Is there a standard literal constant that I can use instead of "utf-8" in C# (.Net 3.5)?

  - by Hamish Grubijan

  Hi, I would like to find a better way to do this: XmlNode nodeXML = xmlDoc.AppendChild( xmlDoc.CreateXmlDeclaration( "1.0", "utf-8", String.Empty) ); I do not want to think about "utf-8" vs "UTF-8" vs "UTF8" vs "utf8" as I type code. I would like to make my code less prone to typos. I am sure that some standard library has declatred "utf-8" as a const / readonly string. How can I find it? Also, what about "1.0"? I am assuming that major XML versions have been enumerated somewhere as well. Thanks!

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• uint8_t and unsigned char linking error

  - by mnn

  I'm using template function: template<typename T> void func(const T& value) { obj->func(value); } where obj is object of class: void my_object::func(int64_t value) { ... } void my_object::func(uint64_t value) { ... } void my_object::func(uint32_t value) { ... } void my_object::func(uint16_t value) { ... } void my_object::func(uint8_t value) { ... } The problem is with uint8_t overload of my_object::func() override. Linker complains about unresolved external symbols to overloads, which should have unsigned char parameter. Should I replace uint8_t overload with unsigned char overload? Edit: Just now noticed, that linker complains about uint64_t and int64_t too. I compile on Windows using MSVC++ 2008 Express.

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• Avoiding "variable might not have been initialized"

  - by Mason Wheeler

  I recently ran across a routine that looks something like this: procedure TMyForm.DoSomething(list: TList<TMyObject>; const flag: boolean); var local: integer; begin if flag then //do something else local := ExpensiveFunctionCallThatCalculatesSomething; //do something else for i := 0 to list.Count do if flag then //do something else if list[i].IntValue > local then //WARNING HERE //do something else end; This gives Variable 'local' might not have been initialized even though you can tell by reading the code that you won't hit that line unless the code branch that initializes it has run. Now, I could get rid of this warning by adding a useless local := 0; at the top of the procedure, but I wonder if there might not be a better way to structure this to avoid the issue. Anyone have any ideas?

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• use callback function to report stack backtrace

  - by user353394

  Assume I have the following: typedef struct { char *name; char binding; int address; } Fn_Symbol //definition of function symbol static Fn_Symbol *fnSymbols; //array of function symbols in a file statc int total; //number of symbol functions in the array and file static void PrintBacktrace(int sigum, siginfo_t * siginfo, void *context) { printf("\nSignal received %d (%s)\n", signum, strsignal(signum)); const int eip_index = 14; void *eip = (void *)((struct ucontext *)context)->uc_mcontext.gregs[eip_index]; printf("Error at [%p] %s (+0x%x), eip, fnName, offset from start); //????? exit(0); } I have this so far, but what is the best way using the fnSymbols static global pointer to identify the function where the error occured and then back trace through the stack to identify each calling function by address, name, and offset?

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• Sql inline query with parameters. Parameter is not read when the query is executed.

  - by fzshah76

  Hi All: I am having a problem with my sql query in c#, basically it's inline query with parameters, but when I run it it tells me that parameter 1 or parameter 2 is not there here is my query declared on top of the page as public: public const string InsertStmtUsersTable = "insert into Users (username, password, email, userTypeID, memberID, CM7Register) " + "Values(@username, @password, @email, @userTypeID, @memberID,@CM7Register ); select @@identity"; this is my code for assigning the parameters, I know I am having problem so I am assigning the params twice: Username =(cmd.Parameters["@username"].Value = row["username"].ToString()) as string; cmd.Parameters["@username"].Value = row["username"].ToString(); In 1 methopd it calls this query and tries to insert to table, here is the code: Result = Convert.ToInt32(SqlHelper.ExecuteScalar(con, CommandType.Text,InsertStmtUsersTable)); Exact error message is: Must declare the variable '@username'.

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• Add every value in stack

  - by rezivor

  I am trying to figure out a method that will add every value in a stack. The goal is to use that value to determine if all the values in the stack are even. I have written to code to do this template <class Object> bool Stack<Object>::objectIsEven( Object value ) const { bool answer = false; if (value % 2 == 0) answer = true; return( answer ); } However, I am stumped on how to add all of the stack's values in a separate method

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• Is There a Good Pattern for Creating a Unique Id based on a Type?

  - by Michael Kelley

  I have a template that creates a unique identifier for each type it is instanced. Here's a streamlined version of the template: template <typename T> class arType { static const arType Id; // this will be unique for every instantiation of arType<>. } // Address of Id is used for identification. #define PA_TYPE_TAG(T) (&arType<T >::Id) This works when you have an executable made purely of static libraries. Unfortunately we're moving to an executable made up of dlls. Each dlls could potentially have its own copy of Id for a type. One obvious solution is to explicitly instantiate all instances of arType. Unfortunately this is cumbersome, and I'd like to ask if anyone can propose a better solution?

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• How to create a string array in matlab?

  - by aduric

  I would like to pass a vector of strings from C++ to matlab. I have tried using the functions available such as mxCreateCharMatrixFromStrings but it doesn't give me the correct behavior. So, I have something like this: void mexFunction( int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) { vector<string> stringVector; stringVector.push_back("string 1"); stringVector.push_back("string 2"); //etc... The problem is how do I get this vector to the matlab environment? plhs[0] = ??? My goal is to be able to run: >> [strings] = MyFunc(...) >> strings(1) = 'string 1'

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• Determine if a string contains only alphanumeric characters (or a space)

  - by dreamlax

  I'm learning C++ and I am writing a function that determines whether a string contains only alphanumeric characters and spaces. I suppose I am effectively testing whether it matches the regular expression ^[[:alnum:] ]+$ but without using regular expressions. I have seen a lot of algorithms revolve around iterators, so I tried to find a solution that made use of iterators, and this is what I have: #include <algorithm> static inline bool is_not_alnum_space(char c) { return !(isalpha(c) || isdigit(c) || (c == ' ')); } bool string_is_valid(const std::string &str) { return find_if(str.begin(), str.end(), is_not_alnum_space) == str.end(); } Is there a better solution, or a “more C++” way to do this?

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• Strange error: cannot convert from 'int' to 'ios_base::openmode'

  - by Dylan Klomparens

  I am using g++ to compile some code. I wrote the following snippet: bool WriteAccess = true; string Name = "my_file.txt"; ofstream File; ios_base::open_mode Mode = std::ios_base::in | std::ios_base::binary; if(WriteAccess) Mode |= std::ios_base::out | std::ios_base::trunc; File.open(Name.data(), Mode); And I receive these errors... any idea why? Error 1: invalid conversion from ‘int’ to ‘std::_Ios_Openmode’ Error 2: initializing argument 2 of ‘std::basic_filebuf<_CharT, _Traits* std::basic_filebuf<_CharT, _Traits::open(const char*, std::_Ios_Openmode) [with _CharT = char, _Traits = std::char_traits]’ As far as I could tell from a Google search, g++ is actually breaking the C++ standard here. Which I find quite astonishing, since they generally conform very strictly to the standard. Is this the case? Or am I doing something wrong. My reference for the standard: http://www.cplusplus.com/reference/iostream/ofstream/open/

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• Problems with delete in destructor

  - by Vera

  Hello, I wrote this code. The constructor works normally, but in the destructor I get "Windows has triggered a breakpoint." How should I correct this? template class CyclicalArray { private: T* mem_ptr; public: CyclicalArray(size_t capacity, const T& default_value) { this->default_value = default_value; this->capacity = capacity; head_index = 0; mem_ptr = ::new T[capacity]; //memory allocating for(T* p = mem_ptr; p < mem_ptr + capacity * sizeof(T); p += sizeof(T)) { ::new (p) T (default_value); //initialization } } ~CyclicalArray() { for(T* p = mem_ptr + sizeof(T); p < mem_ptr + capacity * sizeof(T); p += sizeof(T)) { p->~T(); } delete[] mem_ptr; }

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• For Qt 4.6.x, how to auto-size text to fit in a specified width?

  - by darenchow

  Inside of my QGraphicsRectItem::paint(), I am trying to draw the name of the item within its rect(). However, for each of the different items, they can be of variable width and similarly names can be of variable length. Currently I am starting with a maximum font size, checking if it fits and decrementing it until I find a font size that fits. So far, I haven't been able to find a quick and easy way to do this. Is there a better, or more efficient way to do this? Thanks! void checkFontSize(QPainter *painter, const QString& name) { // check the font size - need a better algorithm... this could take awhile while (painter->fontMetrics().width(name) > rect().width()) { int newsize = painter->font().pointSize() - 1; painter->setFont(QFont(painter->font().family(), newsize)); } }

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• How to load an RSA key from binary data to an RSA structure using the OpenSSL C Library?

  - by Andreas Bonini

  Currently I have my private key saved in a file, private.key, and I use the following function to load it: RSA *r = PEM_read_RSAPrivateKey("private.key", NULL, NULL, NULL); This works perfectly but I'm not happy with the file-based format; I want to save my key in pure binary form (ie, no base64 or similar) in a char* variable and load/save the key from/to it. This way I have much more freedom: I'll be able to store the key directly into the application const char key[] { 0x01, 0x02, ... };, send it over a network socket, etc. Unfortunately though I haven't found a way to do that. The only way to save and load a key I know of reads/saves it to a file directly.

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• CImg compile problems in Codegear 2009

  - by Seth

  I wish to use the CImg library for image processing in my current project. I am using Codegear C++ Builder 2009. I include CImg.h in the source file and put in the following code: int rows =5; int cols = 5; CImg<double> img(rows,cols); I get the following error: [BCC32 Error] CImg.h(39159): E2285 Could not find a match for 'CImg<unsigned char>::move_to<t>(const CImg<unsigned char>)' Does anyone know if there is a #define I should be using when building in Codegear C++ Builder 2009. Or is it simply not compatible?

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• How do I make a class whose interface matches double, but upon which templates can be specialized?

  - by Neil G

  How do I make a class whose interface matches double, but whose templated types do not dynamic cast to double? The reason is that I have a run-time type system, and I want to be able to have a type that works just like double: template<int min_value, int max_value> class BoundedDouble: public double {}; And then inherit use template specialization to get run-time information about that type: template<typename T> class Type { etc. } template<int min_value, int max_value> class Type<BoundedDouble<min_value, max_value>> { int min() const { return min_value; } etc. } But, you can't inherit from double...

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• C++ initializing constants and inheritance

  - by pingvinus

  I want to initialize constant in child-class, instead of base class. And use it to get rid of dynamic memory allocation (I know array sizes already, and there will be a few child-classes with different constants). So I try: class A { public: const int x; A() : x(0) {} A(int x) : x(x) {} void f() { double y[this->x]; } }; class B : A { B() : A(2) {} }; Pretty simple, but compiler says: error C2057: expected constant expression How can I say to compiler, that it is really a constant?

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• How to log C++ exception if running outside debugger, otherwise rethrow

  - by Stefan Monov

  I wanna do something like this: int main() { try { runApp(); } catch(std::exception const& ex) { if(runningInDebugger()) throw; // let the IDE show me what went wrong else displayMsgBox("Something went wrong! " + ex.what()); } } Needs to work at least in VS2008 but the more debuggers it supports, the better. I want it to check for a debugger at runtime. I don't want to do "#ifdef NDEBUG", because I prefer not to do release builds at all (can't be bothered). So what should I use as a "runningInDebugger()" check?

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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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• how to open many files simultaneously for reading in c

  - by monkeyking

  I'm trying to port some of my c++ code into c. I have the following construct class reader{ private: FILE *fp; alot_of_data data;//updated by read_until() method public: reader(const char*filename) read_until(some conditional dependent on the contents of the file, and the arg supplied) } Im then instantiating hundreds of these object and iterate over them using several 'read_until()' for each file until allfiles is at eof. I'm failing to see any clever way to do this in c, the only solution I can come up with is making an array of FILE pointers, and do the same with all the private member data from my class. But this seems very messy, can I implement the functionality of my class as a function pointer, or anything better, I think I'm missing a fundamental design pattern? The files are way to big to have all in memory, so reading everything from every file is not feasible Thanks

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