recursion - C++ deep copy a linked list resursively -


i c++ beginner trying write function create deep copy of linked list in c++. function calls until @ last node in source list, copies node. when run segmentation fault or exc_bad_access error. here have far: 

struct node { int data; node* next; };       void copy_list(const node*& source_ptr, node*& dest_ptr) { if (dest_ptr != nullptr){     clear_list(dest_ptr);     }  if (source_ptr == nullptr) return; //we cleared dest_ptr  if (source_ptr->next == nullptr) // last node {     dest_ptr = new node(); //initialize in memory     dest_ptr->data = source_ptr->data; //copy last datum     dest_ptr->next = nullptr; //since end     return; } const node* cursor = source_ptr->next; // happens if source not yet @ end  copy_list(cursor, dest_ptr->next); }

i know there other questions similar this, haven't helped me. have tried using other methods recursion example while loop looks like:

dest_ptr = new node();  dest_ptr->data = source_ptr->data; node* dest = dest_ptr->next; const node* cursor = source_ptr->next;    while(cursor != nullptr) {     dest = new() node;      dest-> data = cursor->data;     //dest->next = nullptr;     dest = dest->next;     cursor = cursor->next; }

the while loop doesn't give errors copy blank (except first node copied outside while loop).

any appreciated. thanks!

if you're beginner, start simple things: try avoid recursion until understand loops. comment on loop version (recursion bad approach particular problem anyway).

if code doesn't want, should try stepping through in debugger note does, or try explain list of instructions (a rubber duck ideal this, it's patient).

you can approach reasoning code:

each variable should have defined purpose, ideally reflected in name. can see purpose of source_ptr point source list. , purpose of cursor traverse source list.

dest_ptr intended hold newly created copy. you're taking start copying first data it.

what purpose of dest, however? start copy value of dest_ptr->next (which null) it. then, in loop, overwrite dest newly created node. copy cursor->data new node, , copy (uninitialised time) pointer dest->next dest. however, note never read value of dest, overwrite in next iteration.

i suspect intended dest pointer pointer node, , intention this:

dest_ptr = new node(); dest_ptr->data = source_ptr->data; node **dest = &dest_ptr->next; const node *cursor = source->ptr->next;  while (cursor) {   *dest = new node();   (*dest)->data = cursor->data;   dest = &((*dest)->next);   cursor = cursor->next; }

this want, pointers pointers ugly. better use dest second cursor traversing destination list:

dest_ptr = new node(); dest_ptr->data = source_ptr->data; node *dest = dest_ptr; const node *cursor = source_ptr->next;  while (cursor) {   dest->next = new node();   dest = dest->next;   dest->data = cursor->data;   cursor = cursor->next; }

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