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  • How can I pass a C++ member function to a C API as a parameter

    - by michael
    Hi, In my C++ program, I need to call this c API: GConn* gnet_conn_new (const gchar *hostname, gint port, GConnFunc func); where GConnFunc is defined as: void (*GConnFunc) (GConn *conn); My question is if I have a C++ class and have a member function like Class A { public: A(); void my_func (GConn* conn); } In my A::A() Constructor, how can I pass this-myfunc to gnet_conn_new as the GConnFunc parameter? Thank you.

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  • PHP constants declaration based on condition

    - by CM
    I am using one separate file for all constants of my PHP application. class constants { const USERNAME = 'abc'; ........ ........ } For lets say USERNAME constant, value can be either xyz or abc based on file exists check. if xyz file exists USERNAME value would be xyz. How can I do this check in my constants class? Thanks in advance.

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  • avoiding enums as interface identifiers c++ OOP

    - by AlasdairC
    Hi I'm working on a plugin framework using dynamic loaded shared libraries which is based on Eclipse's (and probally other's) extension-point model. All plugins share similar properties (name, id, version etc) and each plugin could in theory satisfy any extension-point. The actual plugin (ie Dll) handling is managed by another library, all I am doing really is managing collections of interfaces for the application. I started by using an enum PluginType to distinguish the different interfaces, but I have quickly realised that using template functions made the code far cleaner and would leave the grunt work up to the compiler, rather than forcing me to use lots of switch {...} statements. The only issue is where I need to specify like functionality for class members - most obvious example is the default plugin which provides a particular interface. A Settings class handles all settings, including the default plugin for an interface. ie Skin newSkin = settings.GetDefault<ISkin>(); How do I store the default ISkin in a container without resorting to some other means of identifying the interface? As I mentioned above, I currently use a std::map<PluginType, IPlugin> Settings::defaults member to achieve this (where IPlugin is an abstract base class which all plugins derive from. I can then dynamic_cast to the desired interface when required, but this really smells of bad design to me and introduces more harm than good I think. would welcome any tips edit: here's an example of the current use of default plugins typedef boost::shared_ptr<ISkin> Skin; typedef boost::shared_ptr<IPlugin> Plugin; enum PluginType { skin, ..., ... } class Settings { public: void SetDefault(const PluginType type, boost::shared_ptr<IPlugin> plugin) { m_default[type] = plugin; } boost::shared_ptr<IPlugin> GetDefault(const PluginType type) { return m_default[type]; } private: std::map<PluginType, boost::shared_ptr<IPlugin> m_default; }; SkinManager::Initialize() { Plugin thedefault = g_settings.GetDefault(skinplugin); Skin defaultskin = boost::dynamic_pointer_cast<ISkin>(theskin); defaultskin->Initialize(); } I would much rather call the getdefault as the following, with automatic casting to the derived class. However I need to specialize for every class type. template<> Skin Settings::GetDefault<ISkin>() { return boost::dynamic_pointer_cast<ISkin>(m_default(skin)); }

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  • windows keydown listeners in C

    - by numerical25
    I am having a very hard time finding resources that talk about the windows message system. Mainly the keydown constant variables. I need to know what const varibles I need to listen for all keypress especially the arrow keys for C

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  • Refactor the following two C++ methods to move out duplicate code

    - by ossandcad
    I have the following two methods that (as you can see) are similar in most of its statements except for one (see below for details) unsigned int CSWX::getLineParameters(const SURFACE & surface, vector<double> & params) { VARIANT varParams; surface->getPlaneParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } unsigned int CSWX::getPlaneParameters(const CURVE & curve, vector<double> & params) { VARIANT varParams; curve->get_LineParams(varParams); // this is the line of code that is different SafeDoubleArray sdParams(varParams); for( int i = 0 ; i < sdParams.getSize() ; ++i ) { params.push_back(sdParams[i]); } if( params.size() > 0 ) return 0; return 1; } Is there any technique that I can use to move the common lines of code of the two methods out to a separate method, that could be called from the two variations - OR - possibly combine the two methods to a single method? The following are the restrictions: The classes SURFACE and CURVE are from 3rd party libraries and hence unmodifiable. (If it helps they are both derived from IDispatch) There are even more similar classes (e.g. FACE) that could fit into this "template" (not C++ template, just the flow of lines of code) I know the following could (possibly?) be implemented as solutions but am really hoping there is a better solution: I could add a 3rd parameter to the 2 methods - e.g. an enum - that identifies the 1st parameter (e.g. enum::input_type_surface, enum::input_type_curve) I could pass in an IDispatch and try dynamic_cast< and test which cast is NON_NULL and do an if-else to call the right method (e.g. getPlaneParams() vs. get_LineParams()) The following is not a restriction but would be a requirement because of my teammates resistance: Not implement a new class that inherits from SURFACE/CURVE etc. (They would much prefer to solve it using the enum solution I stated above)

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  • Execution issue with PyModule_AddIntConstant function

    - by karnol
    I m learning python c api functions and keen to learn python 3.1 stable version. Found an unresolved issue recently and tried PyModule_AddIntConstant(PyObject *module, const char *name, long value) Runtime error occurred for this function call. Is there something wrong with the function in python 3.1?

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  • C# DateTime, is this method regional setting safe?

    - by JL
    I am using the following method to serialize a date as a string private const string DateFormatString = "dd.MM.yyyy HH:mm:ss"; string LastsuccessfuldownloadDateTime = DateTime.Now.AddDays(-91).ToString(DateFormatString); Is this the safest way to ensure that the string always gets serialized in this format?

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  • Get rid of Trailing Numbers in C

    - by Tech163
    For example, #include <stdio.h> int main (int argc, const char * argv[]) { char out = printf("teststring"); printf("%d\n", out); return 0; } will return teststring10. Anyone has an idea how to get rid of the 10? Thanks in advance.

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  • Why are member constants available even if there are no instances of a its class?

    - by flockofcode
    1) Why are member constants available even if there are no instances of a its class? 2) Is the only reason why constant expressions need to be fully evaluated at compile time due to compiler replacing constant variable with literal value? 3) Since string is also an object, I would think the following would produce an error, but it doesn’t. Why? class A { const string b = “it works”; } thank you

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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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  • C++ STL make_heap and pop_heap not working.

    - by Henrique
    I need to use a Heap, so i've searched about the STL one, but it doesn't seem to work, i wrote some code to explain what i mean: #include <stdio.h> #include <stdlib.h> #include <vector> #include <algorithm> struct data { int indice; int tamanho; }; bool comparator2(const data* a, const data* b) { return (a->tamanho < b->tamanho); } int main() { std::vector<data*> mesas; data x1, x2, x3, x4, x5; x1.indice = 1; x1.tamanho = 3; x2.indice = 2; x2.tamanho = 5; x3.indice = 3; x3.tamanho = 2; x4.indice = 4; x4.tamanho = 6; x5.indice = 5; x5.tamanho = 4; mesas.push_back(&x1); mesas.push_back(&x2); mesas.push_back(&x3); mesas.push_back(&x4); mesas.push_back(&x5); make_heap(mesas.begin(), mesas.end(), comparator2); for(int i = 0 ; i < 5 ; i++) { data* mesa = mesas.front(); pop_heap(mesas.begin(),mesas.end()); mesas.pop_back(); printf("%d, %d\n", mesa->indice, mesa->tamanho); } return 0; }; and this is what i get: 4, 6 2, 5 1, 3 3, 2 5, 4 So it's not working as a heap, as the maximum element on the vector is not being returned right. Or am i doing something wrong?

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  • Another getcwd question...

    - by rubenvb
    Sorry to keep hammering on this, but I'm trying to learn :). Is this any good? And yes, I care about memory leaks. I can't find a decent way of preallocating the char*, because there simply seems to be no cross-platform way. const string getcwd() { char* a_cwd = getcwd(NULL,0); string s_cwd(a_cwd); free(a_cwd); return s_cwd; }

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  • Struct with pointer to a function

    - by user354021
    Hello, In a C struct I have defined a function pointer as follows: typedef struct _sequence_t { const int seq[3]; typedef void (* callbackPtr)(); } sequence_t; I want to initialize a var of that type globally with: sequence_t sequences[] = { { { 0, 1, 2 }, toggleArmament }, }; And I keep getting error telling me that there are too many initializers. How to work it out?

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  • 'Good' programming form in maintaining / updating / accessing files by entry

    - by zhermes
    Basic Question: If I'm storying/modifying data, should I access elements of a file by index hard-coded index, i.e. targetFile.getElement(5); via a hardcoded identifier (internally translated into index), i.e. target.getElementWithID("Desired Element"), or with some intermediate DESIRED_ELEMENT = 5; ... target.getElement(DESIRED_ELEMENT), etc. Background: My program (c++) stores data in lots of different 'dataFile's. I also keep a list of all of the data-files in another file---a 'listFile'---which also stores some of each one's properties (see below, but i.e. what it's name is, how many lines of information it has etc.). There is an object which manages the data files and the list file, call it a 'fileKeeper'. The entries of a listFile look something like: filename , contents name , number of lines , some more numbers ... Its definitely possible that I may add / remove fields from this list --- but in general, they'll stay static. Right now, I have a constant string array which holds the identification of each element in each entry, something like: const string fileKeeper::idKeys[] = { "FileName" , "Contents" , "NumLines" ... }; const int fileKeeper::idKeysNum = 6; // 6 - for example I'm trying to manage this stuff in 'good' programatic form. Thus, when I want to retrieve the number of lines in a file (for example), instead of having a method which just retrieves the '3'rd element... Instead I do something like: string desiredID = "NumLines"; int desiredIndex = indexForID(desiredID); string desiredElement = elementForIndex(desiredIndex); where the function indexForID() goes through the entries of idKeys until it finds desiredID then returns the index it corresponds to. And elementForIndex(index) actually goes into the listFile to retrieve the index'th element of the comma-delimited string. Problem: This still seems pretty ugly / poor-form. Is there a way I should be doing this? If not, what are some general ways in which this is usually done? Thanks!

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  • template; operator (int)

    - by Oops
    Hi, regarding my Point struct already mentioned here: http://stackoverflow.com/questions/2794369/template-class-ctor-against-function-new-c-standard is there a chance to replace the function toint() with a cast-operator (int)? namespace point { template < unsigned int dims, typename T > struct Point { T X[ dims ]; //umm??? template < typename U > Point< dims, U > operator U() const { Point< dims, U > ret; std::copy( X, X + dims, ret.X ); return ret; } //umm??? Point< dims, int > operator int() const { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } //OK Point<dims, int> toint() { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } }; //struct Point template < typename T > Point< 2, T > Create( T X0, T X1 ) { Point< 2, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; return ret; } }; //namespace point int main(void) { using namespace point; Point< 2, double > p2d = point::Create( 12.3, 34.5 ); Point< 2, int > p2i = (int)p2d; //äähhm??? std::cout << p2d.str() << std::endl; char c; std::cin >> c; return 0; } I think the problem is here that C++ cannot distinguish between different return types? many thanks in advance. regards Oops

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  • Do I need to cast the result of strtol to int?

    - by Kristo
    The following code does not give a warning with g++ 4.1.1 and -Wall. int octalStrToInt(const std::string& s) { return strtol(s.c_str(), 0, 8); } I was expecting a warning because strtol returns a long int but my function is only returning a plain int. Might other compilers emit a warning here? Should I cast the return value to int in this case as a good practice?

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  • c++ template and its element type

    - by David
    This is my template matrix class: template<typename T> class Matrix { public: .... Matrix<T> operator / (const T &num); } However, in my Pixel class, I didn't define the Pixel/Pixel operator at all! Why in this case, the compiler still compiles?

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