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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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  • 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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  • 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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  • [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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  • 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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  • 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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  • What happens when I throw an exception?

    - by helloWorld
    I have some technical questions. In this function: string report() const { if(list.begin() == list.end()){ throw "not good"; } //do something } If I throw the exception what is going on with the program? Will my function terminate or will it run further? If it terminates, what value will it return?

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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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  • Access Voilation in std::pair

    - by sameer karjatkar
    I have an application which is trying to populate a pair . Out of no where the application crashes . The Windbg analysis on the crash dump suggest PRIMARY_PROBLEM_CLASS: INVALID_POINTER_READ DEFAULT_BUCKET_ID: INVALID_POINTER_READ STACK_TEXT: 0389f1dc EPFilter32!std::vector,std::allocator ::size+0xc INVALID_POINTER_READ_c0000005_Test.DLL!std::vector_std::pair_unsigned_int, unsigned_int_,std::allocator_std::pair_unsigned_int,unsigned_int___::size Following is the statement in the code where it fails const branch_info& b1 = en1.m_branches[i1]; where branch_info is std::pair and the en1.m_branches[i1] fetches me a pair value

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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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  • 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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  • fill an array with Int like a Char; C++, cin object

    - by Duknov007
    This is a pretty simple question; first time poster and long time looker. Here is my binary to decimal converter I wrote: #include <iostream> #include <cmath> using namespace std; const int MAX = 6; int conv(int z[MAX], int l[6], int MAX); int main() { int zelda[MAX]; const int d = 6; int link[d]; cout << "Enter a binary number: \n"; int i = 0; while (i < MAX && (cin >> zelda[i]).get()) //input loop { ++i; } cout << conv(zelda, link, MAX); cin.get(); return 0; } int conv(int zelda[MAX], int link[6], int MAX) { int sum = 0; for (int t = 0; t < MAX; t++) { long int h, i; for (int h = 5, i = 0; h >= 0; --h, ++i) if (zelda[t] == 1) link[h] = pow(2.0, i); else link[h] = 0; sum += link[t]; } return sum; } With the way the input loop is being handled, I have to press enter after each input of a number. I haven't added any error correction yet either (and some of my variables are vague), but would like to enter a binary say 111111 instead of 1 enter, 1 enter, 1 enter, etc to fill the array. I am open to any technique and other suggestions. Maybe input it as a string and convert it to an int? I will keep researching. Thanks.

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  • C++ STL: Trouble with iterators

    - by Rosarch
    I'm having a beginner problem: bool _isPalindrome(const string& str) { return _isPalindrome(str.begin(), str.end()); // won't compile } bool _isPalindrome(string::iterator begin, string::iterator end) { return begin == end || *begin == *end && _isPalindrome(++begin, --end); } What am I doing wrong here? Why doesn't str.begin() get type checked to be a string::iterator?

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