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  • Pointer initialization

    - by SoulBeaver
    Sorry if this question has been asked before. On my search through SO I didn't find one that asked what I wanted to know. Basically, when I have this: typedef struct node { int data; node *node; } *head; and do node *newItem = new node; I am under the impression that I am declaring and reserving space, but not defining, a pointer to struct node, is that correct? So when I do newItem->data = 100 and newItem->next = 0 I get confused. newItem = 0would declare what exactly? Both data and next? The object as a whole? I'm especially confused when I use typedef. Which part is the macro? I assume node because that's how I call it, but why do I need it? Finally, what happens when I do: node *temp; temp = new node; temp = head->next; head->next = newItem; newItem->next = temp; I mean, head-next is a pointer pointing to object newItem, so I assume not to newItem.data or next themselves. So how can I use an uninitialized pointer that I described above safely like here? is head now not pointing to an uninitialized pointer?

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  • "Initializing" the pointer in the separate function in C

    - by pechenie
    I need to do a simple thing, which I used to do many times in Java, but I'm stuck in C (pure C, not C++). The situation looks like this: int *a; void initArray( int *arr ) { arr = malloc( sizeof( int ) * SIZE ); } int main() { initArray( a ); // a is NULL here! what to do?! return 0; } I have some "initializing" function, which SHOULD assign a given pointer to some allocated data (doesn't matter). How should I give a pointer to a function in order to this pointer will be modified, and then can be used further in the code (after that function call returns)? Thanx for help.

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  • Pointing to array element

    - by regular
    What I'm trying to achieve is say i have an array, i want to be able to modify a specific array element throughout my code, by pointing at it. for example in C++ i can do this int main(){ int arr [5]= {1,2,3,4,5}; int *c = &arr[3]; cout << arr[3] <<endl; *c = 0; cout << arr[3]<<endl; } I did some googling and there seems to be a way to do it through 'unsafe', but i don't really want to go that route. I guess i could create a variable to store the indexes, but I'm actually dealing with slightly more complexity (a list within a list. so having two index variables seems to add complexity to the code.) C# has a databinding class, so what I'm currently doing is binding the array element to a textbox (that i have hidden) and modifying that textbox whenever i want to modify the specific array element, but that's also not a good solution (since i have a textbox that's not being used for its intended purpose - a bit misleading).

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  • C++: casting to void* and back

    - by MInner
    * ---Edit - now the whole sourse* When I debug it on the end, "get" and "value" have different values! Probably, I convert to void* and back to User the wrong way? #include <db_cxx.h> #include <stdio.h> struct User{ User(){} int name; int town; User(int a){}; inline int get_index(int a){ return town; } //for another stuff }; int main(){ try { DbEnv* env = new DbEnv(NULL); env->open("./", DB_CREATE | DB_INIT_MPOOL | DB_THREAD | DB_INIT_LOCK | DB_INIT_TXN | DB_RECOVER | DB_INIT_LOG, 0); Db* datab = new Db(env, 0); datab->open(NULL, "db.dbf", NULL, DB_BTREE, DB_CREATE | DB_AUTO_COMMIT, 0); Dbt key, value, get; char a[10] = "bbaaccd"; User u; u.name = 1; u.town = 34; key.set_data(a); key.set_size(strlen(a) + 1 ); value.set_data((void*)&u); value.set_size(sizeof(u)); get.set_flags(DB_DBT_MALLOC); DbTxn* txn; env->txn_begin(NULL, &txn, 0); datab->put(txn, &key, &value, 0); datab->get(txn, &key, &get, 0); txn->commit(0); User g; g = *((User*)&get); printf("%d", g.town); getchar(); return 0; }catch (DbException &e){ printf("%s", e.what()); getchar(); } solution create a kind of "serializator" what would convert all POD's into void* and then will unite these pieces PS Or I'd rewrite User into POD type and everything will be all right, I hope. Add It's strange, but... I cast a defenetly non-pod object to void* and back (it has std::string inside) and it's all right (without sending it to the db and back). How could it be? And after I cast and send 'trough' db defenetly pod object (no extra methods, all members are pod, it's a simple struct {int a; int b; ...}) I get back dirted one. What's wrong with my approach? Add about week after first 'add' Damn... I've compiled it ones, just for have a look at which kind of dirt it returnes, and oh! it's okay!... I can't ! ... AAh!.. Lord... A reasonable question (in 99.999 percent of situations right answer is 'my', but... here...) - whos is this fault? My or VSs?

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  • operator "new" returning a non-local heap pointer for only one class ?

    - by KaluSingh Gabbar
    Language : C++ Platform : Windows Server 2003 I have an exe calling a DLL, in which when I allocate (new) the memory for class A (which is in DLL) it returns me a non-local heap pointer. I try to new other classes which are in DLL and "new" returns a valid heap pointer for them, its only Class A which is not being allocated properly. I am on windows and validating the heap by this function call : _CrtIsValidHeapPointer ( (const void *) pPtr ) I am seriously confused why this only happens with new-ing Class A and no other class ? (All Native Code)

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  • is my function correct?

    - by sbsp
    This is part of an assignment so please dont post solutions, just point me in the right direction if possible? I am passing a pointer to a char array to my method, as well as a value for the actual height of the char array. I am looping through to see if all values are 0, if they are then return 0, esle return one The method is used as a test to see if i should free memory or not and set the pointer to null if it is full of 0's. The issue i am having is that the programme should have "some unfree" memory at the end, so i have no idea whether or not its doing it correctly - and gdb i struggle with immensley. Thanks for reading int shouldBeNull(char *charPointer, int sizeOfCharArray) { int isIn = 0; int i = 0; while(i < sizeOfCharArray){ if(*charPointer != '0'){ isIn = 1; break; } i++; charPointer++; } return isIn; }

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  • From where starts the process' memory space and where does it end?

    - by nhaa123
    Hi, I'm trying to dump memory from my application where the variables lye. Here's the function: void MyDump(const void *m, unsigned int n) { const unsigned char *p = reinterpret_cast<const unsigned char *(m); char buffer[16]; unsigned int mod = 0; for (unsigned int i = 0; i < n; ++i, ++mod) { if (mod % 16 == 0) { mod = 0; std::cout << " | "; for (unsigned short j = 0; j < 16; ++j) { switch (buffer[j]) { case 0xa: case 0xb: case 0xd: case 0xe: case 0xf: std::cout << " "; break; default: std::cout << buffer[j]; } } std::cout << "\n0x" << std::setfill('0') << std::setw(8) << std::hex << (long)i << " | "; } buffer[i % 16] = p[i]; std::cout << std::setw(2) << std::hex << static_cast<unsigned int(p[i]) << " "; if (i % 4 == 0 && i != 1) std::cout << " "; } } Now, how can I know from which address starts my process memory space, where all the variables are stored? And how do I now, how long the area is? For instance: MyDump(0x0000 /* <-- Starts from here? */, 0x1000 /* <-- This much? */); Best regards, nhaa123

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  • correct format for function prototype

    - by yCalleecharan
    Hi, I'm writing to a text file using the following declaration: void create_out_file(char file_name[],long double *z1){ FILE *out; int i; if((out = fopen(file_name, "w+")) == NULL){ fprintf(stderr, "***> Open error on output file %s", file_name); exit(-1); } for(i = 0; i < ARRAY_SIZE; i++) fprintf(out, "%.16Le\n", z1[i]); fclose(out); } Where z1 is an long double array of length ARRAY_SIZE. The calling function is: create_out_file("E:/first67/jz1.txt", z1); I defined the prototype as: void create_out_file(char file_name[], long double z1[]); which I'm putting before "int main" but after the preprocessor directives. My code works fine. I was thinking of putting the prototype as void create_out_file(char file_name[],long double *z1). Is this correct? *z1 will point to the first array element of z1. Is my declaration and prototype good programming practice? Thanks a lot...

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  • Explain this C# code: byte* p = (byte*) (void*) Scan0;

    - by qulzam
    I found the code from the net in which i cant understand this line:- byte* p = (byte*)(void*)Scan0; There Scan0 is System.IntPtr. It is code of C#.Net. Plz Explain the above line. The complete code is given below. this is code to convert a image in grayscale. public static Image GrayScale(Bitmap b) { BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb); int stride = bmData.Stride; System.IntPtr Scan0 = bmData.Scan0; unsafe { byte* p = (byte*)(void*)Scan0; int nOffset = stride - b.Width * 3; byte red, green, blue; for (int y = 0; y < b.Height; ++y) { for (int x = 0; x < b.Width; ++x) { blue = p[0]; green = p[1]; red = p[2]; p[0] = p[1] = p[2] = (byte)(.299 * red + .587 * green + .114 * blue); p += 3; } p += nOffset; } } b.UnlockBits(bmData); return (Image)b; } I understand all the code but only have the problem on this line. byte* p = (byte*)(void*)Scan0;

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  • Is auto_ptr deprecated?

    - by idimba
    Is auto_ptr deprecated in incomming C++ standard? Is unique_ptr should be used for ownershipt transfer instead of share ptr? If unique_ptr is not in standard, than do I need use shared_ptr instead?

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  • Pass 2d array to function in C?

    - by Evelyn
    I know it's simple, but I can't seem to make this work. My function is like so: int GefMain(int array[][5]) { //do stuff return 1; } In my main: int GefMain(int array[][5]); int main(void) { int array[1800][5]; GefMain(array); return 0; } I referred to this helpful resource, but I am still getting the error "warning: passing argument 1 of GefMain from incompatible pointer type." What am I doing wrong?

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  • FORTRAN function returning an array causes a segfault (calling from C++)

    - by Dane Larsen
    Basically, here's my problem. I'm calling someone else's FORTRAN functions from my C++ code, and it's giving me headaches. Some code: function c_error_message() character(len = 255) :: c_error_message errmsg(1:9) = 'ERROR MSG' return end That's the FORTRAN function. My first question is: Is there anything in there that would cause a segfault? If not, then second: What does that return? A pointer? I'm trying to call it with the following C statement: char *e = c_error_message_(); That causes a segfault. c_error_message(); That too causes a segfault. I declared c_error_message_() earlier on with the following code: extern"C" { char* c_error_message_(); } Would declaring a function with a different return type than the actual return type cause a segfault? I'm at a loss. Thanks for any replies.

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  • How can I free all allocated memory at once?

    - by Tommy
    Here is what I am working with: char* qdat[][NUMTBLCOLS]; char** tdat[]; char* ptr_web_data; // Loop thru each table row of the query result set for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru each column of the query result set and extract the data for(col_index = 0; col_index < number_cols; col_index++) { ptr_web_data = (char*) malloc((strlen(Data) + 1) * sizeof(char)); memcpy (ptr_web_data, column_text, strlen(column_text) + 1); qdat[row_index][web_data_index] = ptr_web_data; } } tdat[row_index] = qdat[col_index]; After the data is used, the memory allocated is released one at a time using free(). for(row_index = 0; row_index < number_rows; row_index++) { // Loop thru all columns used for(col_index = 0; col_index < SARWEBTBLCOLS; col_index++) { // Free memory block pointed to by results set array free(tdat[row_index][col_index]); } } Is there a way to release all the allocated memory at once, for this array? Thank You.

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  • how to save poiner in C

    - by JosiP
    Hi In my app, for debugging i want to save pointer, before i do other operations on it eg: void foo(...) { /* suppose ptr1 points to one of my strcuts */ ptr1 = NULL; /* before that ptr1=NULL i want to save value of that pointer - how to do it ? */ } thx for any help

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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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  • Remove pointer object whose reference is mantained in three different lists

    - by brainydexter
    I am not sure how to approach this problem: 'Player' class mantains a list of Bullet* objects: class Player { protected: std::list< Bullet* > m_pBullet_list; } When the player fires a Bullet, it is added to this list. Also, inside the constructor of bullet, a reference of the same object is updated in CollisionMgr, where CollisionMgr also mantains a list of Bullet*. Bullet::Bullet(GameGL*a_pGameGL, Player*a_pPlayer) : GameObject( a_pGameGL ) { m_pPlayer = a_pPlayer; m_pGameGL->GetCollisionMgr()->AddBullet(this); } class CollisionMgr { void AddBullet(Bullet* a_pBullet); protected: std::list< Bullet*> m_BulletPList; } In CollisionMgr.Update(); based on some conditions, I populate class Cell which again contain a list of Bullet*. Finally, certain conditions qualify a Bullet to be deleted. Now, these conditions are tested upon while iterating through a Cell's list. So, if I have to delete the Bullet object, from all these places, how should I do it so that there are no more dangling references to it? std::list< Bullet*>::iterator bullet_it; for( bullet_it = (a_pCell->m_BulletPList).begin(); bullet_it != (a_pCell->m_BulletPList).end(); bullet_it++) { bool l_Bullet_trash = false; Bullet* bullet1 = *bullet_it; // conditions would set this to true if ( l_Bullet_Trash ) // TrashBullet( bullet1 ); continue; } Also, I was reading about list::remove, and it mentions that it calls the destructor of the object we are trying to delete. Given this info, if I delete from one list, the object does not exist, but the list would still contain a reference to it..How do I handle all these problems ? Can someone please help me here ? Thanks PS: If you want me to post more code or provide explanation, please do let me know.

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  • Passing a 2D array to a function in C

    - by Tyler Treat
    I have, essentially, a matrix of data (lets say ints) that I would like to store in a 2D array in which the dimensions are not known until runtime (say x columns and y rows). I want to populate the array in a function, so I assume I need to do something like this: int main(int argc, char **argv) { int y = atoi(argv[1]); int x = atoi(argv[2]); int **matrix = malloc(x * sizeof(int*)); populateMatrix(matrix, y, x); return 0; } void populateMatrix(**matrix, int y, int x) { int i, j; for (i = 0; i < y; i++) { for (j = 0; j < x; j++) { matrix[i][j] = i * j; // populated with trivial data to keep it simple } } } Obviously this doesn't work, but I'm not sure how to do what I'm describing exactly.

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  • [C] this code, its work fine and return what i want, but its hang before print it ??

    - by Rami Jarrar
    I make this program :: #include<stdio.h> char *raw_input(char *msg); main() { char *s; *s = *raw_input("Message Here Is: "); printf("Return Done.."); printf(s); } char *raw_input(char *msg){ char *d; printf("%s", msg); scanf("%s",&d); return d; } What this do is, it print my message and scan for input from the user, then print it,, but whats the problem in print the input from the user ???

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