C++ - Vector index 접근 / 수정 / 삭제

ABOUT Vector index

vector index value 수정

at : access specified element with bounds checking
operator[] : access specified element

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

v.at(4) = -1;
v[4] = 77;

• at and operator[] both return a reference to the indexed element

• you’d better take the habit to use at, less idiomatic, but bound-checking is priceless

• A much better way is to use at(...). This will automatically check for out of bounds behaviour and break throwing an std::out_of_range. So in the case when we have

  v.at(10) = 9;
  

• We will get:
  terminate called after throwing an instance of ‘std::out_of_range’ what(): vector::_M_range_check: __n (which is 10) >= this->size() (which is 4)

• at() 을 쓰는게 좋겠네요. code test 에서 vector로 컨테이너 구현하고 [] 인덱스 접근했더니 시간초과 에러났었음. 앞으로 at()을 쓰도록 합시다

vector - erase : 데이터 삭제

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

int count = 0;
for(vector<int>::iterator it = v.begin(); it != v.end(); it++){
    if(count == 5){//index가 5이면 데이터를 삭제
        it = v.erase(it);
        break;
    }else{
        count++;
    }
}

vector - insert : 데이터 추가

vector <int> v;
for(int i=1;i<=10;i++){
   v.push_back(i);
}

int count = 0;
int i = 0;
for(std::vector<int>::iterator it = v.begin(); it != v.end(); it++){
    if(count == 5){//index가 5이면 데이터를 추가
        v.insert(it,6);
        break;
    }else{
        count++;
    }
}

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