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  • c# Wrapper to native c++ code, wrapping a parameter which is a pointer to an array

    - by mb300dturbo
    Hi, I have the following simple DLL in c++ un-managed code; extern "C" __declspec(dllexport) void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length); void ArrayMultiplier(float (*pointerArray)[3], int scalar, int length) { for (int i = 0 ; i < length ; length++) { for (int j = 0; j < 3; j++) { pointerArray[i][j] = pointerArray[i][j] * scalar; } } } I have tried writing the following wrapper function for the above in c#: [DllImport("sample.dll")] public static extern void ArrayMultiplier(ref float elements, int scalar, int length); where elements is a 2 dimentional 3x3 array: public float[][] elements = { new float[] {2,5,3}, new float [] {4,8,6}, new float [] {5,28,3} }; The code given above compiles, but the program crashes when the wrapper function is called: Wrapper.ArrayMultiplier(ref elements, scalar, length); Please help me here, and tell me whats wrong with the code above, or how a wrapper can be written for a simple c++ function: void SimpleFunction(float (*pointerToArray)[3]); Thank you all in advance

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  • C pointer initialization and dereferencing, what's wrong here?

    - by randombits
    This should be super simple, but I'm not sure why the compiler is complaining here. #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) { int *n = 5; printf ("n: %d", *n); exit(0); } Getting the following complaints: foo.c: In function ‘main’: foo.c:6: warning: initialization makes pointer from integer without a cast I just want to print the value that the pointer n references. I'm dereferencing it in the printf() statement and I get a segmentation fault. Compiling this with gcc -o foo foo.c.

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  • Evaluation of (de)reference operators

    - by Micha
    I have an (uncommented...) source file which I'm trying to understand. static const Map *gCurMap; static std::vector<Map> mapVec; then auto e = mapVec.end(); auto i = mapVec.begin(); while(i!=e) { // ... const Map *map = gCurMap = &(*(i++)); // ... } I don't understand what &(*(i++)) does. It does not compile when just using i++, but to me it looks the same, because I'm "incrementing" i, then I'm requesting the value at the given address and then I'm requesting the address of this value?!

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  • NULL pointer comparison fails

    - by Ilya
    Hello, I'm initializing in a class a pointer to be NULL. Afterwards I check if it is NULL in the same class. But it's not always 0x0. Sometimes it's 0x8 or 0xfeffffff or 0x3f800000 or 0x80 or other strange stuff. In most case the pointer is 0x0 but sometimes it gets altered somehow. I'm sure that I'm not changing it anywhere in my code. Is there a way it gets changed by "itself"? Here's my code: MeshObject::MeshObject() { mesh.vertexColors = NULL; } MeshObject::MeshObject(const MeshObject &_copyFromMe) { SimpleLog("vertexColors pointer: %p", _copyFromMe.mesh.vertexColors); if (_copyFromMe.mesh.vertexColors != NULL) { SimpleLog("vertexColors"); this->mesh.vertexColors = new tColor4i[_copyFromMe.mesh.vertexCount]; memcpy(this->mesh.vertexColors, _copyFromMe.mesh.vertexColors, _copyFromMe.mesh.vertexCount * sizeof(tColor4i) ); } } My application crashes, because vertexColors wasn't initialized and is being copied. However it is NULL and shouldn't be copied. Thanks.

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  • collect string in loop and printout all the string outside loop

    - by user1508163
    I'm newbie here and there is some question that I want have some lesson from you guys. For example: #include <stdio.h> #include<stdlib.h> #include<ctype.h> void main() { char name[51],selection; do { printf("Enter name: "); fflush(stdin); gets(name); printf("Enter another name?(Y/N)"); scanf("%c",&selection); selection=toupper(selection); }while (selection=='Y'); //I want to printout the entered name here but dunno the coding printf("END\n"); system("pause"); } As I know when the loops perform will overwrite the variable then how I perform a coding that will printout all the name user entered? I have already ask my tutor and he is ask me to use pointer, can anyone guide me in this case?

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  • Pointer mysteriously moves

    - by Armen Ablak
    Hi, I have this code for Node rotation and in a line which is marked something happens and I don't really know what and why :). //Test case 30 \ 16 / 29 RotationRight(node->mParent); //call template<class T> void SplayTree<T>::RotationRight(SplayNode<T> *&node) const { SplayNode<T> *left = node->mLeft; SplayNode<T> *parent = node->mParent; node->mLeft = left->mRight; if(left->HasRight()) left->mRight->mParent = node; left->mRight = node; //node in this line points to 0x00445198 {30} left->mParent = node->mParent; //and in this line it points to 0x00444fb8 {16} (node, not node->mParent) node->mParent = left; node = left; } Well, left-mParent points to node also, so I basically do node = node-mParent. The problem is I can't find a work around - how to unpin in from node and change it's pointing address without changing it's.

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  • I can't get that `bus error` to stop sucking.

    - by Koning Baard XIV
    I have this a class called PPString: PPString.h #ifndef __CPP_PPString #define __CPP_PPString #include "PPObject.h" class PPString : public PPObject { char *stringValue[]; public: char *pointerToCharString(); void setCharString(char *charString[]); void setCharString(const char charString[]); }; #endif PPString.cpp #include "PPString.h" char *PPString::pointerToCharString() { return *stringValue; } void PPString::setCharString(char *charString[]) { *stringValue = *charString; } void PPString::setCharString(const char charString[]) { *stringValue = (char *)charString; } I'm trying to set the stringValue using std::cin: main.cpp PPString myString; myString.setCharString("LOLZ"); std::cout << myString.pointerToCharString() << std::endl; char *aa[1000]; std::cin >> *aa; myString.setCharString(aa); std::cout << myString.pointerToCharString() << std::endl; The first one, which uses a const char works, but the second one, with a char doesn't, and I get this output: copy and paste from STDOUT LOLZ im entering a string now... Bus error where the second line is what I entered, followed by pressing the return key. Can anyone help me fixing this? Thanks...

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  • Can somebody please explain this recursive function for me?

    - by capncoolio
    #include <stdio.h> #include <stdlib.h> void reprint(char *a[]) { if(*a) { printf("%d ",a); reprint(a+1); printf("%s ",*a); } } int main() { char *coll[] = {"C", "Objective", "like", "don't", "I", NULL}; reprint(coll); printf("\n"); return EXIT_SUCCESS; } As the more experienced will know, this prints the array in reverse. I don't quite understand how! I need help understanding what reprint(char *a[]) does. I understand pointer arithmetic to a degree, but from inserting printf's here and there, I've determined that the function increments up to the array end, and then back down to the start, only printing on the way down. However, I do not understand how it does this; all I've managed to understand by looking at the actual code is that if *a isn't NULL, then call reprint again, at the next index. Thanks guys!

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  • C++ deleting a pointer

    - by eSKay
    On this page, its written that One reason is that the operand of delete need not be an lvalue. Consider: delete p+1; delete f(x); Here, the implementation of delete does not have a pointer to which it can assign zero. Adding a number to a pointer shifts it forward in memory by those many number of sizeof(*p) units. So, what is the difference between delete p and delete p+1, and why would making the pointer 0 only be a problem with delete p+1?

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  • Could I ever want to access the address zero?

    - by Joel
    The constant 0 is used as the null pointer in C and C++. But as in http://stackoverflow.com/questions/2389251/pointer-to-a-specific-fixed-address there seems to be some possible use of assigning fixed addresses. Is there ever any conceivable need, in any system, for whatever low level task, for accessing the address 0? If there is, how is that solved with 0 being the null pointer and all? If not, what makes it certain that there is not such a need?

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  • Acessing a struct member, using a pointer to a vector of structs. Error:base operand of '->' has non-pointer type

    - by Matt Munson
    #include <iostream> #include <vector> using namespace std; struct s_Astruct { vector <int> z; }; int main () { vector <s_Astruct> v_a; for(int q=0;q<10;q++) { v_a.push_back(s_Astruct()); for(int w =0;w<5;w++) v_a[q].z.push_back(8); } vector <s_Astruct> * p_v_a = & v_a; cout << p_v_a[0]->z[4]; //error: base operand of '->' has non-pointer type //'__gnu_debug_def::vector<s_Astruct, std::allocator<s_Astruct> >' } There seems to be some issue with this sort of operation that I don't understand. In the code that I'm working on I actually have things like p_class-vector[]-vector[]-int; and I'm getting a similar error.

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  • why no implicit conversion from pointer to reference to const pointer.

    - by user316606
    I'll illustrate my question with code: #include <iostream> void PrintInt(const unsigned char*& ptr) { int data = 0; ::memcpy(&data, ptr, sizeof(data)); // advance the pointer reference. ptr += sizeof(data); std::cout << std::hex << data << " " << std::endl; } int main(int, char**) { unsigned char buffer[] = { 0x11, 0x11, 0x11, 0x11, 0x22, 0x22, 0x22, 0x22, }; /* const */ unsigned char* ptr = buffer; PrintInt(ptr); // error C2664: ... PrintInt(ptr); // error C2664: ... return 0; } When I run this code (in VS2008) I get this: error C2664: 'PrintInt' : cannot convert parameter 1 from 'unsigned char *' to 'const unsigned char *&'. If I uncomment the "const" comment it works fine. However shouldn't pointer implicitly convert into const pointer and then reference be taken? Am I wrong in expecting this to work? Thanks!

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  • How to return a copy of the data in C++

    - by Josh Curren
    I am trying to return a new copy of the data in a C++ Template class. The following code is getting this error: invalid conversion from ‘int*’ to ‘int’. If I remove the new T then I am not returning a copy of the data but a pointer to it. template<class T> T OrderedList<T>::get( int k ) { Node<T>* n = list; for( int i = 0; i < k; i++ ) { n=n->get_link(); } return new T( n->get_data() ); // This line is getting the error ********** }

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  • Check if a pointer points to allocated memory on the heap.

    - by Ugo
    Ok, I know this question seems to have been asked many times on stackoverflow. but please read Well the answer for any address is "No you can't" but the question here is to know if a pointer points to a piece of memory allocated with malloc/new. Actually I think it could be easily implemented overriding malloc/free and keeping track of allocated memory ranges. Do you know a memory management library providing this specific tool ?

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  • What does this pointer-heavy C code do?

    - by justRadojko
    Could someone explain to me what should two following lines do: s.httpheaderline[s.httpheaderlineptr] = *(char *)uip_appdata; ++((char *)uip_appdata); This is taken from uIP code for microcontrollers. s - structure httpheaderline - http packet presented as a string httpheadrlineptr - integer value uip_appdata - received ethernet packet (string) If some more info is needed please let me know. BTW. Eclipse is reporting an error on the second line with message Invalid lvalue in increment so i'm trying to figure out how to solve this.

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  • Class lookup structure array in C++

    - by wyatt
    I'm trying to create a structure array which links input strings to classes as follows: struct {string command; CommandPath cPath;} cPathLookup[] = { {"set an alarm", AlarmCommandPath}, {"send an email", EmailCommandPath}, {"", NULL} }; which will be used as follows: CommandPath *cPath = NULL; string input; getline(cin, input); for(int i = 0; cPathLookup[i] != ""; i++) { if(cPathLookup[i].command == input) cPath = new cPathLookup[i].cPath; } Obviously, this code is meaningless, but I think my intention is apparent - depending on input, I'd like cPath to be initialized as either a new AlarmCommandPath or a new EmailCommandPath. I could handle it with a function returning an instance depending on input, but a whole sequence of ifs just seems inelegant. I should also note that, in case it's not apparent and important, that AlarmCommandPath and EmailCommandPath are derived from CommandPath, and CommandPath is an abstract class. Thanks for any help you can offer. EDIT: I just noticed that, in spite of CommandPath being abstract, I have a declaration: CommandPath *cPath = NULL; in working code. Why does that compile?

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  • casting char[][] to char** causes segfault?

    - by Earlz
    Ok my C is a bit rusty but I figured I'd make my next(small) project in C so I could polish back up on it and less than 20 lines in I already have a seg fault. This is my complete code: #define ROWS 4 #define COLS 4 char main_map[ROWS][COLS+1]={ "a.bb", "a.c.", "adc.", ".dc."}; void print_map(char** map){ int i; for(i=0;i<ROWS;i++){ puts(map[i]); //segfault here } } int main(){ print_map(main_map); //if I comment out this line it will work. puts(main_map[3]); return 0; } I am completely confused as to how this is causing a segfault. What is happening when casting from [][] to **!? That is the only warning I get. rushhour.c:23:3: warning: passing argument 1 of ‘print_map’ from incompatible pointer type rushhour.c:13:7: note: expected ‘char **’ but argument is of type ‘char (*)[5]’ Are [][] and ** really not compatible pointer types? They seem like they are just syntax to me.

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  • How to convert a void pointer to array of classes

    - by user99545
    I am trying to convert a void pointer to an array of classes in a callback function that only supports a void pointer as a means of passing paramaters to the callback. class person { std::string name, age; }; void callback (void *val) { for (int i = 0; i < 9; i++) { std::cout << (person [])val[i].name; } } int main() { person p[10]; callback((void*)p); } My goal is to be able to pass an array of the class person to the callback which then prints out the data such as their name and age. However, the compile does not like what I am doing and complains that error: request for member 'name' in 'val', which is of non-class type 'void*' How can I go about doing this?

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  • How can I return to a string address and then assign it to a new string?

    - by Y_Y
    I have 1 function that I want to return the address of an assigned string to the main function and assign an new string pointer with the same address so that the new string will have the contents of the old string. For example: unknown_datatype function() { char *old = "THE STRING"; return old; } int main() { char *snew = ""; snew = function(); return 0; } *unknown_datatype means I don't know that to put there... *How can I approach this without changing anything in the main() method

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  • C problem, left of '->' must point to class/struct/union/generic type ??

    - by Patrick
    Hello! Trying to understand why this doesn't work. I keep getting the following errors: left of '-nextNode' must point to class/struct/union/generic type (Also all the lines with a - in the function new_math_struct) Header file #ifndef MSTRUCT_H #define MSTRUCT_H #define PLUS 0 #define MINUS 1 #define DIVIDE 2 #define MULTIPLY 3 #define NUMBER 4 typedef struct math_struct { int type_of_value; int value; int sum; int is_used; struct math_struct* nextNode; } ; typedef struct math_struct* math_struct_ptr; #endif C file int get_input(math_struct_ptr* startNode) { /* character, input by the user */ char input_ch; char* input_ptr; math_struct_ptr* ptr; math_struct_ptr* previousNode; input_ptr = &input_ch; previousNode = startNode; /* as long as input is not ok */ while (1) { input_ch = get_input_character(); if (input_ch == ',') // Carrage return return 1; else if (input_ch == '.') // Illegal character return 0; if (input_ch == '+') ptr = new_math_struct(PLUS, 0); else if (input_ch == '-') ptr = new_math_struct(MINUS, 0); else if (input_ch == '/') ptr = new_math_struct(DIVIDE, 0); else if (input_ch == '*') ptr = new_math_struct(MULTIPLY, 0); else ptr = new_math_struct(NUMBER, atoi(input_ptr)); if (startNode == NULL) { startNode = previousNode = ptr; } else { previousNode->nextNode = ptr; previousNode = ptr; } } return 0; } math_struct_ptr* new_math_struct(int symbol, int value) { math_struct_ptr* ptr; ptr = (math_struct_ptr*)malloc(sizeof(math_struct_ptr)); ptr->type_of_value = symbol; ptr->value = value; ptr->sum = 0; ptr->is_used = 0; return ptr; } char get_input_character() { /* character, input by the user */ char input_ch; /* get the character */ scanf("%c", &input_ch); if (input_ch == '+' || input_ch == '-' || input_ch == '*' || input_ch == '/' || input_ch == ')') return input_ch; // A special character else if (input_ch == '\n') return ','; // A carrage return else if (input_ch < '0' || input_ch > '9') return '.'; // Not a number else return input_ch; // Number } The header for the C file just contains a reference to the struct header and the definitions of the functions. Language C.

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  • char pointer array in c#

    - by james
    consider the following c++ code #include "stdafx.h" #include<iostream> using namespace std; void ping(int,char* d[]); void ping(int a,char *b[]) { int size; size=sizeof(b)/sizeof(int); // total size of array/size of array data type //cout<<size; for(int i=0;i<=size;i++) cout<<"ping "<<a<<b[i]<<endl; } int _tmain(int argc, _TCHAR* argv[]) { void (*funcptr)(int,char* d[]); char* c[]={"a","b"}; funcptr= ping; funcptr(10,c); return 0; } how can i implement the same in c#.. m new to c#. how can i have char pointer array in c#?

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  • How do I return the indices of a multidimensional array element in C?

    - by Eddy
    Say I have a 2D array of random boolean ones and zeroes called 'lattice', and I have a 1D array called 'list' which lists the addresses of all the zeroes in the 2D array. This is how the arrays are defined: define n 100 bool lattice[n][n]; bool *list[n*n]; After filling the lattice with ones and zeroes, I store the addresses of the zeroes in list: for(j = 0; j < n; j++) { for(i = 0; i < n; i++) { if(!lattice[i][j]) // if element = 0 { list[site_num] = &lattice[i][j]; // store address of zero site_num++; } } } How do I extract the x,y coordinates of each zero in the array? In other words, is there a way to return the indices of an array element through referring to its address?

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