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  • Template meta-programming with member function pointers?

    - by wheaties
    Is it possible to use member function pointers with template meta-programming? Such as: class Connection{ public: string getName() const; string getAlias() const; //more stuff }; typedef string (Connection::*Con_Func)() const; template<Con_Func _Name> class Foo{ Connection m_Connect; public: void Foo(){ cout << m_Connect.(*_Name); } }; typedef Foo<&Connection::getName> NamedFoo; typedef Foo<&Connection::getAlias> AliasFoo; Granted, this is rather contrived but is it possible? (yes, there are probably much better ways but humor me.)

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  • Can I use memcpy in C++ to copy classes that have no pointers or virtual functions

    - by Shane MacLaughlin
    Say I have a class, something like the following; class MyClass { public: MyClass(); int a,b,c; double x,y,z; }; #define PageSize 1000000 MyClass Array1[PageSize],Array2[PageSize]; If my class has not pointers or virtual methods, is it safe to use the following? memcpy(Array1,Array2,PageSize*sizeof(MyClass)); The reason I ask, is that I'm dealing with very large collections of paged data, as decribed here, where performance is critical, and memcpy offers significant performance advantages over iterative assignment. I suspect it should be ok, as the 'this' pointer is an implicit parameter rather than anything stored, but are there any other hidden nasties I should be aware of?

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  • Basic help needed with pointers

    - by sbsp
    Hi, i asked some time ago on an account i cant remember how to manipulate basic pointers and someone gave me a really good demo for example char *ptr = hello (hello = a char array) so now *ptr is pointing at h ptr++ = moves the ptr to point at the next element, to get its value i do *ptr and that gives me e ok so far i hope :D but now i need to manipulate a char **ptr and was wondering how i do this in a way that mimmicks the effects of a 2d array? some basic tips would be much appreciated as i need to do an assignment that has a **ptr to immitate a 2d array and without knowing how it does this first means i cant even solve it on paper (for example, how do you dereference a **ptr, how do you get [x][y] values etc) thanks

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  • Prob comparing pointers and integer in C

    - by Dimitri
    Hi I have a problem with this code. When i am using this function I have no warnings. : void handler(int sig){ switch(sig) { case SIGINT : { click++; fprintf(stdout,"SIGINT recu\n"); if( click == N){ exit(0); } } case SIGALRM : fprintf(stdout,"SIGALRM received\n"); exit(0); case SIGTERM: fprintf(stdout,"SIGTERM received\n"); exit(0); } } But when i rewrite the function with this new version, I have a " comparison between pointer and integer" warning on the if statement: void handler( int sig){ printf("Signal recu\n"); if( signal == SIGINT){ click++; fprintf(stdout,"SIGINT received; Click = %d\n",click); if(click == N){ fprintf(stdout,"Exiting with SIGINT\n"); exit(0); } } else if(signal == SIGALRM){ fprintf(stdout,"SIGALRM received\n"); exit(0); } else if(signal == SIGTERM){ fprintf(stdout,"SIGTERM received\n"); exit(0); } Can someone tell me where is the prob?

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  • Basic help needed with pointers (double indirection)

    - by sbsp
    Hi, i asked some time ago on an account i cant remember how to manipulate basic pointers and someone gave me a really good demo for example char *ptr = "hello" (hello = a char array) so now *ptr is pointing at h ptr++ = moves the ptr to point at the next element, to get its value i do *ptr and that gives me e ok so far i hope :D but now i need to manipulate a char **ptr and was wondering how I do this in a way that mimmicks the effects of a 2d array? some basic tips would be much appreciated as I need to do an assignment that has a **ptr to imitate a 2d array and without knowing how it does this first means I cant even solve it on paper (for example, how do you dereference a **ptr, how do you get [x][y] values etc) thanks

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  • Why do they initialize pointers this way?

    - by Rob
    In almost all of the books I read and examples I go through I see pointers initialized this way. Say that I have a class variable NSString *myString that I want to initialize. I will almost always see that done this way: -(id)init { if (self = [super init]) { NSString *tempString = [[NSString alloc] init]; myString = tempString; [tempString release]; } return self; } Why can't I just do the following? -(id)init { if (self = [super init]) { myString = [[NSString alloc] init]; } return self; } I don't see why the extra tempString is ever needed in the first place, but I could be missing something here with memory management. Is the way I want to do things acceptable or will it cause some kind of leak? I have read the Memory Management Guide on developer.apple.com and unless I am just missing something, I don't see the difference.

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  • pointers in C with a #define

    - by milan
    The function: #define ASSOC(port) (*(volatile bit_field *) (&port)) The function call: #define SCLK ASSOC(PORTC).bit0 bit_field defined as a struct like this: typedef struct { unsigned char bit0 :1, bit1 :1, bit2 :1, bit3 :1, bit4 :1, bit5 :1, bit6 :1, bit7 :1; } bit_field; I don't know where &port is defined. Can someone please explain how the function is read and how it works please? I am not very good with pointers and this example in particular is very confusing with "*" in the front and at the end and the "&" with the port. Thank you

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  • Problem with passing array of pointers to struct among functions in C

    - by karatemonkey
    The Code that follows segfaults on the call to strncpy and I can't see what I am doing wrong. I need another set of eyes to look it this. Essentially I am trying to alloc memory for a struct that is pointed to by an element in a array of pointers to struct. #include <stdio.h> #include <stdlib.h> #include <string.h> #define MAX_POLICY_NAME_SIZE 64 #define POLICY_FILES_TO_BE_PROCESSED "SPFPolicyFilesReceivedOffline\0" typedef struct TarPolicyPair { int AppearanceTime; char *IndividualFile; char *FullPolicyFile; } PolicyPair; enum { bwlist = 0, fzacts, atksig, rules, MaxNumberFileTypes }; void SPFCreateIndividualPolicyListing(PolicyPair *IndividualPolicyPairtoCreate ) { IndividualPolicyPairtoCreate = (PolicyPair *) malloc(sizeof(PolicyPair)); IndividualPolicyPairtoCreate->IndividualFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->FullPolicyFile = (char *)malloc((MAX_POLICY_NAME_SIZE * sizeof(char))); IndividualPolicyPairtoCreate->AppearanceTime = 0; memset(IndividualPolicyPairtoCreate->IndividualFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); memset(IndividualPolicyPairtoCreate->FullPolicyFile, '\0', (MAX_POLICY_NAME_SIZE * sizeof(char))); } void SPFCreateFullPolicyListing(SPFPolicyPair **CurrentPolicyPair, char *PolicyName, char *PolicyRename) { int i; for(i = 0; i < MaxNumberFileTypes; i++) { CreateIndividualPolicyListing((CurrentPolicyPair[i])); // segfaults on this call strncpy((*CurrentPolicyPair)[i].IndividualFile, POLICY_FILES_TO_BE_PROCESSED, (SPF_POLICY_NAME_SIZE * sizeof(char))); } } int main() { SPFPolicyPair *CurrentPolicyPair[MaxNumberFileTypes] = {NULL, NULL, NULL, NULL}; int i; CreateFullPolicyListing(&CurrentPolicyPair, POLICY_FILES_TO_BE_PROCESSED, POLICY_FILES_TO_BE_PROCESSED); return 0; }

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  • Array-size macro that rejects pointers

    - by nneonneo
    The standard array-size macro that is often taught is #define ARRAYSIZE(arr) (sizeof(arr) / sizeof(arr[0])) or some equivalent formation. However, this kind of thing silently succeeds when a pointer is passed in, and gives results that can seem plausible at runtime until things mysteriously fall apart. It's all-too-easy to make this mistake: a function that has a local array variable is refactored, moving a bit of array manipulation into a new function called with the array as a parameter. So, the question is: is there a "sanitary" macro to detect misuse of the ARRAYSIZE macro in C, preferably at compile-time? In C++ we'd just use a template specialized for array arguments only; in C, it seems we'll need some way to distinguish arrays and pointers. (If I wanted to reject arrays, for instance, I'd just do e.g. (arr=arr, ...) because array assignment is illegal).

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  • free( ) pointers

    - by user1043625
    I'm required to use a special library to keep track of my memory leaks where malloc()= allocate( ) and free( ) = unallocate( ). I'm trying to complete free a linked-list but it seems like the "root" value isn't being freed. typedef struct _node { struct _node *child; char *command; } Command_list; void delete_commands(Command_list **root) { Command_list *temp; while( *root != NULL ){ temp = (*root)->child; //printf("STRING: %s\n", *root->command ); unallocate( *root ); *root = temp; } } The function that's calling it void file_processing( .... ){ Command_list *root = allocate(sizeof (Command_list)); root = NULL; .... delete_commands( &root ); } } I believe that Command_list *root = allocate(sizeof (Command_list)) isn't being properly de-allocated for some reason. Anyone can give me some hints? UPDATE: I found out that instead of Command_list *root = allocate(sizeof (Command_list)); root = NULL; this works: Command_list *root = NULL;

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  • c++ Multiple Inheritance - Compiler modifying my pointers

    - by Bob
    If I run the following code, I get different addresses printed. Why? class Base1 { int x; }; class Base2 { int y; }; class Derived : public Base1, public Base2 { }; union U { Base2* b; Derived* d; U(Base2* b2) : b(b) {} }; int main() { Derived* d = new Derived; cout << d << "\n"; cout << U(d).d << "\n"; return 0; } Even more fun is if you repeatedly go in and out of the union the address keeps incrementing by 4, like this int main() { Derived* d = new Derived; cout << d << "\n"; d = U(d).d; cout << d << "\n"; d = U(d).d; cout << d << "\n"; return 0; } If the union is modified like this, then the problem goes away union U { void* v; Base2* b; Derived* d; U(void* v) : v(v) {} }; Also, if either base class is made empty, the problem goes away. Is this a compiler bug? I want it to leave my pointers the hell alone.

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  • What's wrong with my destructor?

    - by Ahmed Sharara
    // Sparse Array Assignment.cpp : Defines the entry point for the console application. // #include "stdafx.h" #include<iostream> using namespace std; struct node{ int row; int col; int value; node* next_in_row; node* next_in_col; }; class MultiLinkedListSparseArray { private: char *logfile; node** rowPtr; node** colPtr; // used in constructor node* find_node(node* out); node* ins_node(node* ins,int col); node* in_node(node* ins,node* z); node* get(node* in,int row,int col); bool exist(node* so,int row,int col); node* dummy; int rowd,cold; //add anything you need public: MultiLinkedListSparseArray(int rows, int cols); ~MultiLinkedListSparseArray(); void setCell(int row, int col, int value); int getCell(int row, int col); void display(); void log(char *s); void dump(); }; MultiLinkedListSparseArray::MultiLinkedListSparseArray(int rows,int cols){ rowPtr=new node* [rows+1]; colPtr=new node* [cols+1]; for(int n=0;n<=rows;n++) rowPtr[n]=NULL; for(int i=0;i<=cols;i++) colPtr[i]=NULL; rowd=rows;cold=cols; } MultiLinkedListSparseArray::~MultiLinkedListSparseArray(){ cout<<"array is deleted"<<endl; for(int i=rowd;i>=0;i--){ for(int j=cold;j>=0;j--){ if(exist(rowPtr[i],i,j)) delete get(rowPtr[i],i,j); } } // it stops in the last loop & doesnt show the done word cout<<"done"<<endl; delete [] rowPtr; delete [] colPtr; delete dummy; } void MultiLinkedListSparseArray::log(char *s){ logfile=s; } void MultiLinkedListSparseArray::setCell(int row,int col,int value){ if(exist(rowPtr[row],row,col)){ (*get(rowPtr[row],row,col)).value=value; } else{ if(rowPtr[row]==NULL){ rowPtr[row]=new node; (*rowPtr[row]).value=value; (*rowPtr[row]).row=row; (*rowPtr[row]).col=col; (*rowPtr[row]).next_in_row=NULL; (*rowPtr[row]).next_in_col=NULL; } else if((*find_node(rowPtr[row])).col<col){ node* out; out=find_node(rowPtr[row]); (*out).next_in_row=new node; (*((*out).next_in_row)).col=col; (*((*out).next_in_row)).row=row; (*((*out).next_in_row)).value=value; (*((*out).next_in_row)).next_in_row=NULL; } else if((*find_node(rowPtr[row])).col>col){ node* ins; ins=in_node(rowPtr[row],ins_node(rowPtr[row],col)); node* g=(*ins).next_in_row; (*ins).next_in_row=new node; (*((*ins).next_in_row)).col=col; (*(*ins).next_in_row).row=row; (*(*ins).next_in_row).value=value; (*(*ins).next_in_row).next_in_row=g; } } } int MultiLinkedListSparseArray::getCell(int row,int col){ return (*get(rowPtr[row],row,col)).value; } void MultiLinkedListSparseArray::display(){ for(int i=1;i<=5;i++){ for(int j=1;j<=5;j++){ if(exist(rowPtr[i],i,j)) cout<<(*get(rowPtr[i],i,j)).value<<" "; else cout<<"0"<<" "; } cout<<endl; } } node* MultiLinkedListSparseArray::find_node(node* out) { while((*out).next_in_row!=NULL) out=(*out).next_in_row; return out; } node* MultiLinkedListSparseArray::ins_node(node* ins,int col){ while(!((*ins).col>col)) ins=(*ins).next_in_row; return ins; } node* MultiLinkedListSparseArray::in_node(node* ins,node* z){ while((*ins).next_in_row!=z) ins=(*ins).next_in_col; return ins; } node* MultiLinkedListSparseArray::get(node* in,int row,int col){ dummy=new node; dummy->value=0; while((*in).col!=col){ if((*in).next_in_row==NULL){ return dummy; } in=(*in).next_in_row; } return in; } bool MultiLinkedListSparseArray::exist(node* so,int row,int col){ if(so==NULL) return false; else{ while((*so).col!=col){ if((*so).next_in_row==NULL) return false; else so=(*so).next_in_row; } return true; } }

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  • Getting Segmentation Fault in C++, but why?

    - by Carlos
    I am getting segmentation fault in this code but i cant figure out why. I know a segmentation fault happens when a pointer is NULL, or when it points to a random memory address. #include <iostream> #include <fstream> #include <cmath> using namespace std; //**************************** CLASS ******************************* class Database { struct data{ string city; float latitude, longitude; data *link; }*p; public: Database(); void display(); void add(string cityName, float lat, float lon); private: string cityName; float lat, lon; }; //************************** CLASS METHODS ************************** Database::Database() { p = NULL; } void Database::add(string cityName, float lat, float lon){ data *q, *t; if(p == NULL){ p = new data; p -> city = cityName; p -> latitude = lat; p -> longitude = lon; p -> link = NULL; } else{ q = p; while(q -> link != NULL){ q = q -> link; } t = new data; t -> city = cityName; t -> latitude = lat; t -> longitude = lon; q -> link = t; } } void Database::display() { data *q; cout<<endl; for( q = p ; q != NULL ; q = q->link ) cout << endl << q -> city; } //***************************** MAIN ******************************* //*** INITIALIZATION *** Database D; void loadDatabase(); //****** VARIABLES ***** //******* PROGRAM ****** int main() { loadDatabase(); D.display(); } void loadDatabase() { int i = 0; string cityName; float lat, lon; fstream city; city.open("city.txt", ios::in); fstream latitude; latitude.open("lat.txt", ios::in); fstream longitude; longitude.open("lon.txt", ios::in); while(!city.eof()){ //************************************ city >> cityName; //* * latitude >> lat; //Here is where i think is the problem longitude >> lon; //* * D.add(cityName, lat, lon); //************************************ } city.close(); latitude.close(); longitude.close(); } This is the error am actually getting in console

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  • How to overwrite an array of char pointers with a larger list of char pointers?

    - by Casey
    My function is being passed a struct containing, among other things, a NULL terminated array of pointers to words making up a command with arguments. I'm performing a glob match on the list of arguments, to expand them into a full list of files, then I want to replace the passed argument array with the new expanded one. The globbing is working fine, that is, g.gl_pathv is populated with the list of expected files. However, I am having trouble copying this array into the struct I was given. #include <glob.h> struct command { char **argv; // other fields... } void myFunction( struct command * cmd ) { char **p = cmd->argv; char* program = *p++; // save the program name (e.g 'ls', and increment to the first argument glob_t g; memset(&g, 0, sizeof(g)); g.gl_offs = 1; int res = glob(*p++, GLOB_DOOFFS, NULL, &g); glob_handle_res(res); while (*p) { res = glob(*p, GLOB_DOOFFS | GLOB_APPEND, NULL, &g); glob_handle_res(res); } if( g.gl_pathc <= 0 ) { globfree(&g); } cmd->argv = malloc((g.gl_pathc + g.gl_offs) * sizeof *cmd->argv); if (cmd->argv == NULL) { sys_fatal_error("pattern_expand: malloc failed\n");} // copy over the arguments size_t i = g.gl_offs; for (; i < g.gl_pathc + g.gl_offs; ++i) cmd->argv[i] = strdup(g.gl_pathv[i]); // insert the original program name cmd->argv[0] = strdup(program); ** cmd->argv[g.gl_pathc + g.gl_offs] = 0; ** globfree(&g); } void command_free(struct esh_command * cmd) { char ** p = cmd->argv; while (*p) { free(*p++); // Segfaults here, was it already freed? } free(cmd->argv); free(cmd); } Edit 1: Also, I realized I need to stick program back in there as cmd-argv[0] Edit 2: Added call to calloc Edit 3: Edit mem management with tips from Alok Edit 4: More tips from alok Edit 5: Almost working.. the app segfaults when freeing the command struct Finally: Seems like I was missing the terminating NULL, so adding the line: cmd->argv[g.gl_pathc + g.gl_offs] = 0; seemed to make it work.

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  • Function to swap pointers in Objective-C

    - by Michael
    - (void) swapController:(MyViewController*)controller1 with:(MyViewController*)controller2 { MyViewController *swap = controller2; controller2 = controller1; controller1 = swap; } Looks like this doesn't work because I'm not passing references. How to do it anyway?

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  • Pointers in c/c++

    - by jammkie same
    include void main() { int p[]={0,1,2,3,4}; int *a[]={p,p+1,p+2,p+3,p+4}; printf("%u %u %u %u",a,a,(*a)); } What should be the output of the above code? And if we make array p as static(static int p[]), output gets changed .Why?

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  • How to copy an array of char pointers with a larger list of char pointers?

    - by Casey Link
    My function is being passed a struct containing, among other things, a NULL terminated array of pointers to words making up a command with arguments. I'm performing a glob match on the list of arguments, to expand them into a full list of files, then I want to replace the passed argument array with the new expanded one. The globbing is working fine, that is, g.gl_pathv is populated with the list of expected files. However, I am having trouble copying this array into the struct I was given. #include <glob.h> struct command { char **argv; // other fields... } void myFunction( struct command * cmd ) { char **p = cmd->argv; char* program = *p++; // save the program name (e.g 'ls', and increment to the first argument glob_t g; memset(&g, 0, sizeof(g)); int res = glob(*p, 0, NULL, &g); *p++ // increment while (*p) { glob(*p++, GLOB_APPEND, NULL, &g); // append the matches } // here i want to replace cmd->argv with the expanded g.gl_pathv memcpy(cmd->argv, g.gl_pathv, g.gl_pathc ); // this doesn't work globfree(&g); }

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  • Problem with passing vector of pointers to objects to member function of another object

    - by Jamesz
    Hi, I have a vector of pointers to Mouse objects called 'mice'. I'm passing the mice to the cat by reference. vector <Mouse*> mice; Cat * c; c->lookForMouse(&mice); And here's my lookForMouse() member function void Cat::lookForMouse(vector <Mouse*> *mice) { ... } And now to the problem! Within the function above, I can't seem to access my mice. This below will not work mice[i]->isActive(); The error message I receive suggests to use mice[i].isActive(), but this throws an error saying isActive() is not a member of std::vector<_Ty ... This works though... vector <Mouse*> miceCopy = *mice; miceCopy[i]->isActive(); I understand that I shouldn't be creating another vector of mice here, it defeats the whole point of passing it by reference (let me know if I'm wrong)... Why can't I do mice[i]-isActive() What should I be doing? Thanks for your time and help :D James.

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  • C++ design question, container of instances and pointers

    - by Tom
    Hi all, Im wondering something. I have class Polygon, which composes a vector of Line (another class here) class Polygon { std::vector<Line> lines; public: const_iterator begin() const; const_iterator end() const; } On the other hand, I have a function, that calculates a vector of pointers to lines, and based on those lines, should return a pointer to a Polygon. Polygon* foo(Polygon& p){ std::vector<Line> lines = bar (p.begin(),p.end()); return new Polygon(lines); } Here's the question: I can always add a Polygon (vector Is there a better way that dereferencing each element of the vector and assigning it to the existing vector container? //for line in vector<Line*> v //vcopy is an instance of vector<Line> vcopy.push_back(*(v.at(i)) I think not, but I dont really like that approach. Hopefully, I will be able to convince the author of the class to change it, but I cant base my coding right now to that fact (and i'm scared of a performance hit). Thanks in advance.

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  • C++ Function pointers vs Switch

    - by Perfix
    What is faster: Function pointers or switch? The switch statement would have around 30 cases, consisting of enumarated unsigned ints from 0 to 30. I could do the following: class myType { FunctionEnum func; string argv[123]; int someOtherValue; }; // In another file: myType current; // Iterate through a vector containing lots of myTypes // ... for ( i=0; i < myVecSize; i ++ ) switch ( current.func ) { case 1: //... break; // ........ case 30: // blah break; } And go trough the switch with func every time. The good thing about switch would also be that my code is more organized than with 30 functions. Or I could do that (not so sure with that): class myType { myReturnType (*func); string argv[123]; int someOtherValue; }; I'd have 30 different functions then, at the beginning a pointer to one of them is assigned to myType. What is probably faster: Switch statement or function pointer? Calls per second: Around 10 million. I can't just test it out - that would require me to rewrite the whole thing. Currently using switch. I'm building an interpreter which I want to be faster than Python & Ruby - every clock cycle matters!

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  • deleting an array that stores pointers to some objects

    - by memC
    hi, I am storing pointers to elements of a vec_A in an array A* a_ptrs[3] . Assume that vec_A will not be resized. So, a_ptrs[i] will point to the correct element. My question is: Suppose A* a_ptrs[3] is declared in a class B. Since it is not created using 'new' I am guessing I don't need to delete it in the destructor. Am I right?? class A { public: int getNumber(); A(int val); ~A(){}; private: int num; }; A::A(int val){ num = val; }; int A::getNumber(){ return num; }; int main(){ int i =0; int num; std::vector<A> vec_A; for ( i = 0; i < 10; i++){ vec_A.push_back(A(i)); } A* a_ptrs[3]; a_ptrs[0] = &vec_A[0]; a_ptrs[1] = &vec_A[3]; a_ptrs[2] = &vec_A[5]; for (i = 0; i<3; i++){ std::cout<<"\n: a_ptrs[i].getNumber() = "<<a_ptrs[i]->getNumber(); } std::cout << "\nPress RETURN to continue..."; std::cin.get(); return 0; }

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  • Pointer arithmetic and arrays: what's really legal?

    - by bitcruncher
    Consider the following statements: int *pFarr, *pVarr; int farr[3] = {11,22,33}; int varr[3] = {7,8,9}; pFarr = &(farr[0]); pVarr = varr; At this stage, both pointers are pointing at the start of each respective array address. For *pFarr, we are presently looking at 11 and for *pVarr, 7. Equally, if I request the contents of each array through *farr and *varr, i also get 11 and 7. So far so good. Now, let's try pFarr++ and pVarr++. Great. We're now looking at 22 and 8, as expected. But now... Trying to move up farr++ and varr++ ... and we get "wrong type of argument to increment". Now, I recognize the difference between an array pointer and a regular pointer, but since their behaviour is similar, why this limitation? This is further confusing to me when I also consider that in the same program I can call the following function in an ostensibly correct way and in another incorrect way, and I get the same behaviour, though in contrast to what happened in the code posted above!? working_on_pointers ( pFarr, farr ); // calling with expected parameters working_on_pointers ( farr, pFarr ); // calling with inverted parameters . void working_on_pointers ( int *pExpect, int aExpect[] ) { printf("%i", *pExpect); // displays the contents of pExpect ok printf("%i", *aExpect); // displays the contents of aExpect ok pExpect++; // no warnings or errors aExpect++; // no warnings or errors printf("%i", *pExpect); // displays the next element or an overflow element (with no errors) printf("%i", *aExpect); // displays the next element or an overflow element (with no errors) } Could someone help me to understand why array pointers and pointers behave in similar ways in some contexts, but different in others? So many thanks. EDIT: Noobs like myself could further benefit from this resource: http://www.panix.com/~elflord/cpp/gotchas/index.shtml

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  • How to access pixels of an NSBitmapImageRep?

    - by Paperflyer
    I have an NSBitmapImageRep that is created like this: NSBitmapImageRep *imageRep = [[NSBitmapImageRep alloc] initWithBitmapDataPlanes:NULL pixelsWide:waveformSize.width pixelsHigh:waveformSize.height bitsPerSample:8 samplesPerPixel:4 hasAlpha:YES isPlanar:YES colorSpaceName:NSCalibratedRGBColorSpace bytesPerRow:0 bitsPerPixel:0]; Now I want to access the pixel data so I get a pointer to the pixel planes using unsigned char *bitmapData; [imageRep getBitmapDataPlanes:&bitmapData]; According to the Documentation this returns a C array of five character pointers. But how can it do that? since the type of the argument is unsigned char **, it can only return an array of chars, but not an array of char pointers. So, this leaves me wondering how to access the individual pixels. Do you have an idea how to do that? (I know there is the method – setColor:atX:y:, but it seems to be pretty slow if invoked for every single pixel of a big bitmap.)

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  • Call by Reference Function in C

    - by Chad
    Hello everyone, I would just like a push in the right direction here with my homework assignment. Here is the question: (1) Write a C function called input which returns void, this function prompts the user for input of two integers followed by a double precision value. This function reads these values from the keyboard and finds the product of the two integers entered. The function uses call by reference to communicate the values of the three values read and the product calculated back to the main program. The main program then prints the three values read and the product calculated. Provide test results for the input: 3 5 23.5. Do not use arrays or global variables in your program. And here is my code: #include <stdio.h> #include <stdlib.h> void input(int *day, int *month, double *k, double *pro); int main(void){ int i,j; double k, pro; input(&i, &j, &k, &pro); printf("%f\n", pro); return 0; } void input(int *i, int *j, double *k, double *pro){ int x,y; double z; double product; scanf("%d", &x); scanf("%d", &y); scanf("%f", &z); *pro += (x * y * z); } I can't figure out how to reference the variables with pointers really, it is just not working out for me. Any help would be great!

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  • Function pointer arrays in Fortran

    - by Eduardo Dobay
    I can create function pointers in Fortran 90, with code like real, external :: f and then use f as an argument to another function/subroutine. But what if I want an array of function pointers? In C I would just do double (*f[])(int); to create an array of functions returning double and taking an integer argument. I tried the most obvious, real, external, dimension(3) :: f but gfortran doesn't let me mix EXTERNAL and DIMENSION. Is there any way to do what I want? (The context for this is a program for solving a system of differential equations, so I could input the equations without having a million parameters in my subroutines.)

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