C++ vector delete problem

Question

n3r3d 0 Newbie Poster

16 Years Ago

I have this class :
int br=0; // br is counter how much records i hold in my vector

class racunalo{
      public:
      void upis(string naziv, string velicinaRam, string velicinaHDD, string brzina, string proizvodac);  
      void upisKomp();  
      string getNaziv(int s) const;
      void pregled();
      void upisDat();
      void pregledNaziv();
      void pregledProizvodac();
      void brisanjeRac();
      string getVelicinaRam(int s) const;
      string getVelicinaHDD(int s) const;
      string getVelicinaBrzina(int s) const;
      string getProizvodac(int s) const;
      string getBrzina(int s) const;
      void ispisKomp();
      private:
      struct komp{
             string naziv;
             string velicinaRam;
             string velicinaHDD;
             string brzina;
             string proizvodac;
             };
      vector<komp>racunala;
      
        };

and i want to delete record from vector racunala

i tried to write function like this:

void racunalo::brisanjeRac(){
cout<<"Enter computer name you want to delete:"<<endl;
string comp_name;
cin>>comp_name;
for(int i=0;i<br;i++){
if(kompjuteri.getNaziv(i) == comp_name){
racunala.erase(racunala.begin()+i);}
     }}

but it doesnt work. Lets say i got 2 records in my file.

Acer
Toshiba

when i try to delete Acer it doesn't delete but it get replaced by Toshiba so i get output like

Toshiba
Toshiba

Please help me, thank you in advance.

c++

3 Contributors
7 Replies
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Latest Post 16 Years Ago Latest Post by n3r3d

Dani AI

Generated 7 Months Ago

Short diagnosis and concrete fixes (ties to earlier replies by and ):

You’re operating on the wrong object and a separate counter. In your brisanjeRac you create a fresh racunalo rac; and then call methods on rac. That new object’s vector is empty, so indexing it causes undefined behavior (hangs, crashes, or strange output). Also keeping a global br that mirrors vector size is fragile — use racunala.size() instead. As warned, delete from the same container you print; as suggested, consider remove_if for a clean removal.

Safe, simple member implementation (erase–remove idiom):

void racunalo::brisanjeRac() {
    cout << "Enter computer name you want to delete: ";
    string comp_name;
    if (!(cin >> comp_name)) return;

    // requires <algorithm>
    auto it = std::remove_if(racunala.begin(), racunala.end(),
        [&](const komp &k){ return k.naziv == comp_name; });

    if (it == racunala.end()) {
        cout << "No matching record.\n";
    } else {
        racunala.erase(it, racunala.end());
        cout << "Deleted matching entries.\n";
    }
}

Further practical tips

Remove the global br. Use racunala.size() (type size_t) or provide a size() accessor. That prevents index/length mismatches.
If you must erase while looping, iterate backwards or decrement the index after an erase to avoid skipping the next element.
Change file input to while (datoteka >> naziv >> ram >> ...) (not while(!eof())) to avoid duplicate/partial reads.
If callers need to modify elements, return references (komp& get_komp(size_t)) or provide explicit mutators/erase functions — don’t expose the internal vector unless intended.

Run small tests (one, two, several matches) after these changes. That will eliminate the undefined behavior and make deletions behave predictably.

All 7 Replies

Clinton Portis 211 Practically a Posting Shark

16 Years Ago

Why are you trying to access a second element, in a 1 element vector?

Unless I am missing something..

//I think this...
if(kompjuteri.getNaziv(i) == comp_name){
     racunala.erase(racunala.begin()+i);}

//Should be this:
if(racunala[i].naziv == comp_name){
     racunala.erase(racunala.begin()+i);}

Edited 16 Years Ago by Clinton Portis because: n/a

mrnutty 761 Senior Poster

16 Years Ago

Can you use remove_if ?

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Clinton Portis 211 Practically a Posting Shark · Answer 1 · 2009-12-10T00:40:09+00:00

You need access to the vector as it is a private member of class racunalo.

getNaziv() does not do this for you, as it returns a 'string'

few possible options:

make racunala public.
create an accessor function that will return a pointer to racunala.
declare a public iterator to racunala.
create an accessor function that will return a private iterator
declare the struct and vector outside the scope of the class.

n3r3d 0 Newbie Poster · Answer 2 · 2009-12-10T01:21:41+00:00

You need access to the vector as it is a private member of class racunalo.
getNaziv() does not do this for you, as it returns a 'string'
few possible options:
make racunala public.

create an accessor function that will return a pointer to racunala.

declare a public iterator to racunala.

create an accessor function that will return a private iterator

declare the struct and vector outside the scope of the class.

Thank you, in my assignment i got, there is written racunala must be in private section so i cant use that option. I cant use last one either.
Other three i don't know how to make. Can u give me some example or something else.

Thank you so far.

n3r3d 0 Newbie Poster · Answer 3 · 2009-12-10T01:23:51+00:00

Can you use remove_if ?

Maybe i could, but i dont know how should i write it.

Why are you trying to access a second element, in a 1 element vector?

Unless I am missing something..
//I think this...
if(kompjuteri.getNaziv(i) == comp_name){
     racunala.erase(racunala.begin()+i);}

//Should be this:
if(racunala[i].naziv == comp_name){
     racunala.erase(racunala.begin()+i);}

No, i cannot use racunala, as its in private section and i cannot access to it direct.

Clinton Portis 211 Practically a Posting Shark · Answer 4 · 2009-12-10T02:14:19+00:00

Try this:

class racunalo
{
     private:

          struct komp
          {
               string naziv;
               string velicinaRam;
               string velicinaHDD;
               string brzina;
               string proizvodac;
         };

          vector<komp> racunala;         

     public:

          komp get_komp(int index){return racunala[index];}
          vector<komp> get_rac(){return racunala;}
          void erase(int element){racunala.erase(racuanala.begin()+element);}
          void erase(int first, int last){racunala.erase(racunala.begin()+first, racunala.begin()+last);}
};

int main()
{
     racunalo rac;
 
     for(int i=0; i<br; i++)
     {
          if(rac.get_komp(i).naziv == comp_name)
          {
               rac.erase(i);
               br--;
               i--;
          }
     }
     return 0;
}

n3r3d 0 Newbie Poster · Answer 5 · 2009-12-10T19:27:14+00:00

Try this:

class racunalo
{
     private:

          struct komp
          {
               string naziv;
               string velicinaRam;
               string velicinaHDD;
               string brzina;
               string proizvodac;
         };

          vector<komp> racunala;         

     public:

          komp get_komp(int index){return racunala[index];}
          vector<komp> get_rac(){return racunala;}
          void erase(int element){racunala.erase(racuanala.begin()+element);}
          void erase(int first, int last){racunala.erase(racunala.begin()+first, racunala.begin()+last);}
};

int main()
{
     racunalo rac;
 
     for(int i=0; i<br; i++)
     {
          if(rac.get_komp(i).naziv == comp_name)
          {
               rac.erase(i);
               br--;
               i--;
          }
     }
     return 0;
}

I tried like u wrote here, it starts but when i enter comp_name and press enter program stop responding.

void racunalo::brisanjeRac(){
racunalo rac;
cout<<"Enter computer name you want to delete:"<<endl;
string comp_name;
cin>>comp_name;
for(int i=0;i<br;i++){
if(rac.get_komp(i).naziv == comp_name){
rac.erase(i);
br--;
i--;}
}
}

Here is complete program:

#include <iostream>
#include <string>
#include <vector>
#include <fstream>
using namespace std;
int br=0;
class racunalo{
      public:
      void upis(string naziv, string velicinaRam, string velicinaHDD, string brzina, string proizvodac);  
      void upisKomp();  
      string getNaziv(int s) const;
      void pregled();
      void upisDat();
      void pregledNaziv();
      void pregledProizvodac();

      void brisanjeRac();
      string getVelicinaRam(int s) const;
      string getVelicinaHDD(int s) const;
      string getVelicinaBrzina(int s) const;
      string getProizvodac(int s) const;
      string getBrzina(int s) const;
      void ispisKomp();
      private:
      struct komp{
             string naziv;
             string velicinaRam;
             string velicinaHDD;
             string brzina;
             string proizvodac;
             };
            vector<komp>racunala;
            komp get_komp(int index){return racunala[index];}
vector<komp> get_rac(){return racunala;}
void erase(int element){racunala.erase(racunala.begin()+element);}
void erase(int first, int last){racunala.erase(racunala.begin()+first, racunala.begin()+last);}
        };
racunalo kompjuteri;        
        
        
void racunalo::upis(string nazivNew, string velicinaRamNew, string velicinaHDDNew, string brzinaNew, string proizvodacNew){
     komp temp;
     temp.naziv = nazivNew;
     temp.velicinaRam = velicinaRamNew;
     temp.velicinaHDD = velicinaHDDNew;
     temp.brzina = brzinaNew;
     temp.proizvodac = proizvodacNew;
     br++;
     racunala.push_back(temp);
     }

string racunalo::getNaziv(int s) const
{return racunala[s].naziv;
}
string racunalo::getVelicinaRam(int s) const
{return racunala[s].velicinaRam;
}
string racunalo::getVelicinaHDD(int s) const
{return racunala[s].velicinaHDD;
}
string racunalo::getBrzina(int s) const
{return racunala[s].brzina;
}
string racunalo::getProizvodac(int s) const
{return racunala[s].proizvodac;
}
void racunalo::ispisKomp(){
                cout<<"Naziv"<<endl;
     for(int i=0;i<br;i++){
cout<<kompjuteri.getNaziv(i)<<endl;               
             }
     }
     //upis
void racunalo::upisKomp(){
     ifstream datoteka;
     string naziv,ram,hdd,brzina,proizvodac;
     datoteka.open("ducan.txt");
     while(!datoteka.eof()){
     datoteka >> naziv >> ram >> hdd >> brzina >> proizvodac;
     racunalo::upis(naziv,ram,hdd,brzina,proizvodac);}
     cout<<"Podaci iz datoteke su ucitani!"<<endl;
     system("pause");
     }
void racunalo::pregledNaziv(){
     cout<<"Unesite naziv racunala:"<<endl;
     string naziv;
     cin>>naziv;
     system("cls");
     cout<<"Naziv\tRam\tHDD\tBrzina\tProizvodac"<<endl;
     for(int i=0;i<br;i++){
             if(kompjuteri.getNaziv(i) == naziv){
             cout<<kompjuteri.getNaziv(i)<<"\t\t"<<kompjuteri.getVelicinaRam(i)<<"\t"<<kompjuteri.getVelicinaHDD(i)<<"\t"<<kompjuteri.getBrzina(i)<<"\t"<<kompjuteri.getProizvodac(i)<<endl;}}
     }    

void racunalo::brisanjeRac(){
racunalo rac;
cout<<"Enter computer name you want to delete:"<<endl;
string comp_name;
cin>>comp_name;
for(int i=0;i<br;i++){
if(rac.get_komp(i).naziv == comp_name){
rac.erase(i);
br--;
i--;}
}
}

//upis u datoteku
void racunalo::upisDat(){
     int brojac=0;
     ofstream datoteka;
     datoteka.open("ducan.txt");
     for(int i=0;i<br;i++){
     datoteka<<kompjuteri.getNaziv(i)<<" "<<kompjuteri.getVelicinaRam(i)<<" "<<kompjuteri.getVelicinaHDD(i)<<" "<<kompjuteri.getBrzina(i)<<" "<<kompjuteri.getProizvodac(i)<<endl;
     brojac++;}
     cout<<brojac<<" racunala je upisano u datoteku ducan.txt ."<<endl;
     }
     
     
void racunalo::pregledProizvodac(){
     cout<<"Unesite proizvodaca racunala:"<<endl;
     string naziv;
     cin>>naziv;
     system("cls");
     cout<<"Naziv\tRam\tHDD\tBrzina\tProizvodac"<<endl;
     for(int i=0;i<br;i++){
             if(kompjuteri.getProizvodac(i) == naziv){
             cout<<kompjuteri.getNaziv(i)<<"\t\t"<<kompjuteri.getVelicinaRam(i)<<"\t"<<kompjuteri.getVelicinaHDD(i)<<"\t"<<kompjuteri.getBrzina(i)<<"\t"<<kompjuteri.getProizvodac(i)<<endl;}}
     }    
     //pregled
void racunalo::pregled(){
     system("cls");
     cout<<"Prema kojem kriteriju zelite pregledati racunala:"<<endl;
     cout<<"1.Prema nazivu"<<endl;
     cout<<"2.Prema proizvodacu"<<endl;
     int izbor;
     cin>>izbor;
     switch(izbor){
                   case 1:
                        kompjuteri.pregledNaziv();
                        system("pause");
                        break;
                   case 2:
                        kompjuteri.pregledProizvodac();
                        system("pause");
                        break;
                        };
     }
     //meni
void meni(){
     for(;;){
     system("cls");
     cout<<"MENI"<<endl;
     cout<<"1. Unos podataka iz datoteke"<<endl;
     cout<<"2. Ispis podataka o racunalu"<<endl;
     cout<<"3. Brisanje podataka odabranog racunala"<<endl;
     cout<<"4. Pregled podataka o racunalima prema odredenom kriteriju"<<endl;
     int izbor;
     cin>>izbor;
     switch(izbor){
                   case 1:
                         kompjuteri.upisKomp();
                         break;
                   case 2:
                        kompjuteri.upisDat();
                        system("pause");
                        break;
                   case 3:
                        kompjuteri.brisanjeRac();
                        break;
                   case 4:
                        kompjuteri.pregled();
                        break;
                   case 5:
                        kompjuteri.ispisKomp();
                        system("pause");
                        break;
                         }}}     
int main(){
    meni();
    system("pause");}

I dont know where is error. Can you look at it and see.

P.S. Hrvatska = ljepe žene :))

C++ vector delete problem

Dani AI

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