pointer assignments not holding through multiple functions c++ -

i'm writing small program simulate schedulers inside os , during execution noticing when assign new value head pointer of linked list not carry on next function. if don't have written.

//insert @ head of event queue if(ecursor == ehead){     cout << "insert @ head" << endl;     eve->prev =  null;     eve->next = ecursor;     ecursor->prev = eve;     ehead = eve;     ecursor = eve; } 

ive double checked insert login make sure im not missing anything, , works other insertions. @ point never assigns head pointer correctly.

after insert head pointer read main body of program displays time @ event take place (presumably event in made head equal to)

event type: 2

check events in queue

ecount: 1

check event order

eve->time: 0.0667091

ecursor->time: 0.0108831

insert after tail

scheduling arrival: 1

event type: 1

check events in queue

ecount: 1

check event order

eve->time: 0.015281

ecursor->time: 0.0667091

insert @ head

clock: 0.0667091

type 1: arrival

type 2: departure

as can see last insertion inserted @ head , new head time should inserted event time clock not show change.

here of program reference

void insert_event(struct event* eve) { ecursor = ehead;  cout << "event type: " << eve->type << endl;  cout << "check no events in queue" << endl;  cout << "ecount: " << ecount << endl;  if(ecount == 0){      ehead = eve;      eve->next = null;      eve->prev = null;      etail = ehead; }   //if newevent preceded other events/event queue not empty else{     cout << "check event order" << endl;     //insert new arrival event queue     do{         cout << "eve->time: " << eve->time << endl;         cout << "ecursor->time: " << ecursor->time << endl;         //new arrival earlier event cursor points          if(ecursor->time >= eve->time){              //insert @ head of event queue             if(ecursor == ehead){                 cout << "insert @ head" << endl;                 eve->prev =  null;                 eve->next = ecursor;                 ecursor->prev = eve;                 ehead = eve;                 ecursor = eve;             }              //insert inside of event queue             else{                 cout << "insert inside " << endl;                 ecursor->prev->next = eve;                 eve->next = ecursor;                 eve->prev = ecursor->prev;                  ecursor->prev = eve;             }             break;         }          //new arrival after final event in event queue         //insert @ tail of event queue         else if(ecursor == etail && (ecursor->time < eve->time)){             cout << "insert after tail" << endl;             ecursor->next = eve;             eve->prev = ecursor;             etail = eve;             break;         }          ecursor = ecursor->next;     }while(ecursor != null);      //reset ecursor head of event queue     ecursor = ehead;   //increment event queue count ecount++; }   int process_event_arr(struct event* eve){  cout << "processing arrival: " << pacount << endl;  //generate new process struct process* proc = new process;   //process time starts proc->start = simclock;  //generate service time process proc->sertime = genexp(1/ts);  //if no processes service, service arrival instantly //add departure event if(!server_busy){      phead = proc;     schedule_event_dep(proc);     server_busy = true;      //set cpu proc     incpu = proc; }  //behavior process queueing else{      //non premptive     if(stype == 1 || stype == 3)         //process ready queue         phead->next = proc;         phead = proc;     } }  //remove arrival event queue remove_event(eve); eve = null;  //schedule new arrival event schedule_event_arr();  //increment process count pcount++; pacount++; }  int process_event_dep(struct event* eve){  pcursor = phead; cout << "processing dep: " << depcount << endl; //process completed process eve->link->finish = simclock;  cout << " if no ready queue release cpu" << endl; if(pcount == 0)     server_busy = false;  else{     cout << "creating temp process" << endl;     struct process* temp = new process;      cout << "assigning temp process cursor time" << endl;     temp->start = pcursor->start;      cout << "schedule next process" << endl;     switch(stype){         case 1:     //fcfs                                             if(pcursor->start < temp->start)                             temp = pcursor;                          pcursor = pcursor->next;                     while(pcursor != null);                      schedule_event_dep(temp);                     incpu = temp;                     break;         default:                     //error                     break;     }; };  //remove event event queue/process ready queue remove_event(eve); eve = null;  //incremement departure count //decrement process/event count dcount++;    pcount--; ecount--; }   int run_sim(){  struct event* eve = new event; while(!(dcount > 10000)){      eve = ehead;     simclock = eve->time;     cout << "clock: " << simclock << endl;     switch (eve->type){          case arr:             process_event_arr(eve);             break;         case dep:             process_event_dep(eve);             break;         case qtum:             process_event_tslice(eve);             break;         default:             //error             break;      }     ehead = eve->next;     free(eve);     eve = null; }  return 0; }