std::vector. STL vector class. 사용법.

 

 

개요. - std::vector

 

- 동적 배열이면서 배열의 마지막 지점에 엘리먼트 삽입  , 제거 에 최적화 되어있음. 

- push_back()  마지막에 엘리먼트 삽입.
- pop_back() 마지막 엘리먼트 삭제. 

- 마지막 아닌곳도 엘리먼트 삽입, 삭제 가능하긴 함. 
- vector 는 메모리에 연속 배치됨. 

 비교
 - std::deque  마지막 과 앞 모두 엘리먼트 삽입제거 가능. 메모리에 불연속 배치됨. 

헤더파일 : vector , #include <vector>

기본 문법.

 

std::vector

 

The STL vector class is a template class of sequence containers that arrange elements of a given type in a linear arrangement and allow fast random access to any element. They should be the preferred container for a sequence when random-access performance is at a premium.

Syntax

 

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Copy

template < class Type, class Allocator = allocator<Type> > class vector

Parameters

 

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TypeThe element data type to be stored in the vectorAllocatorThe type that represents the stored allocator object that encapsulates details about the vector's allocation and deallocation of memory. This argument is optional and the default value is allocator<Type>.

Remarks

 

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Vectors allow constant time insertions and deletions at the end of the sequence. Inserting or deleting elements in the middle of a vector requires linear time. The performance of the deque Class container is superior with respect to insertions and deletions at the beginning and end of a sequence. The list Class container is superior with respect to insertions and deletions at any location within a sequence.
Vector reallocation occurs when a member function must increase the sequence contained in the vector object beyond its current storage capacity. Other insertions and erasures may alter various storage addresses within the sequence. In all such cases, iterators or references that point at altered portions of the sequence become invalid. If no reallocation happens, only iterators and references before the insertion/deletion point remain valid.
The vector<bool> Class is a full specialization of the template class vector for elements of type bool with an allocator for the underlying type used by the specialization.
The vector<bool> reference Class is a nested class whose objects are able to provide references to elements (single bits) within a vector<bool> object.

Members

 

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Constructors

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vector

Constructs a vector of a specific size or with elements of a specific value or with a specific allocator or as a copy of some other vector.

Typedefs

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allocator_type	A type that represents the allocator class for the vector object.
const_iterator	A type that provides a random-access iterator that can read a const element in a vector.
const_pointer	A type that provides a pointer to a const element in a vector.
const_reference	A type that provides a reference to a const element stored in a vector for reading and performing const operations.
const_reverse_iterator	A type that provides a random-access iterator that can read any const element in the vector.
difference_type	A type that provides the difference between the addresses of two elements in a vector.
iterator	A type that provides a random-access iterator that can read or modify any element in a vector.
pointer	A type that provides a pointer to an element in a vector.
reference	A type that provides a reference to an element stored in a vector.
reverse_iterator	A type that provides a random-access iterator that can read or modify any element in a reversed vector.
size_type	A type that counts the number of elements in a vector.
value_type	A type that represents the data type stored in a vector.

Member Functions

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assign	Erases a vector and copies the specified elements to the empty vector.
at	Returns a reference to the element at a specified location in the vector.
back	Returns a reference to the last element of the vector.
begin	Returns a random-access iterator to the first element in the vector.
capacity	Returns the number of elements that the vector could contain without allocating more storage.
cbegin	Returns a random-access const iterator to the first element in the vector.
cend	Returns a random-access const iterator that points just beyond the end of the vector.
crbegin	Returns a const iterator to the first element in a reversed vector.
crend	Returns a const iterator to the end of a reversed vector.
clear	Erases the elements of the vector.
data	Returns a pointer to the first element in the vector.
emplace	Inserts an element constructed in place into the vector at a specified position.
emplace_back	Adds an element constructed in place to the end of the vector.
empty	Tests if the vector container is empty.
end	Returns a random-access iterator that points to the end of the vector.
erase	Removes an element or a range of elements in a vector from specified positions.
front	Returns a reference to the first element in a vector.
get_allocator	Returns an object to the allocator class used by a vector.
insert	Inserts an element or a number of elements into the vector at a specified position.
max_size	Returns the maximum length of the vector.
pop_back	Deletes the element at the end of the vector.
push_back	Add an element to the end of the vector.
rbegin	Returns an iterator to the first element in a reversed vector.
rend	Returns an iterator to the end of a reversed vector.
reserve	Reserves a minimum length of storage for a vector object.
resize	Specifies a new size for a vector.
shrink_to_fit	Discards excess capacity.
size	Returns the number of elements in the vector.
swap	Exchanges the elements of two vectors.

Operators

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operator[]	Returns a reference to the vector element at a specified position.
operator=	Replaces the elements of the vector with a copy of another vector.

Requirements

Header: <vector>
Namespace: std

 

 

 

 

std::vector 생성자 사용예 

 

#include <vector>


  std::vector<int> first;                                // empty vector of ints
  std::vector<int> second (4,100);                       // four ints with value 100
  std::vector<int> third (second.begin(),second.end());  // iterating through second
  std::vector<int> fourth (third);                       // a copy of third

  // the iterator constructor can also be used to construct from arrays:
  int myints[] = {16,2,77,29};
  std::vector<int> fifth (myints, myints + sizeof(myints) / sizeof(int) );

 

 

루프

std::vector<i> my_vec;

my_vec.push_back(345); // 345 를 my_vec 마지막에 추가 
my_vec.push_back(3); // 3을 my_vec 마지막에 추가 

// 일반 배열처럼 루프
for(int i = 0 ; i<my_vec.size() ; i++)
{
   my_vec.at(i);// my_vec[i] 로 해도 됨. 
}

// iterator 를 이용한 루프 . 
vector<int>::iterator iter;
for(iter = my_vec.begin(); iter != my_vec.end(); iter++)
{
  *iter; //iterator 는 엘리먼트 주소를 받는 포인터이므로 값을 받기 위해서 * 부착.
}

// auto 이용한 루프
for(auto iter : my_vec)// 엘리먼트의 값을 복사해서 iter 에  넣어줌. 
{
    iter; // 값이 복사된 것이므로 iter 그냥 사용. 
}

 

 

////////// 엘리먼트 받기 

my_vec.at(idx); // idx에 해당하는 것 

my_vec[idx]; // idx 에 해당하는 것

my_vec.front(); // 첫번째 것

my_vec.back(); // 마지막 것


///// 특정 엘리먼트에 값 대입. 
my_vec.at(idx) = 값;
my_vec[idx] - 값;


///// 엘리먼트 삽입. 

my_vec.push_back(element); // 마지막에 삽입.

my_vec.insert(iter, element); // iter 에 element 삽입. 뒤의것은 밀림.

my_vec.insert(iter,5 ,element); // iter 에 5개의 element 삽입. 뒤의것은 밀림. 


///// 제거 
my_vec.pop_back() ; // 마지막것 제거. 

my_vec.clear() ; // 모두 제거. 

my_vec.erase(iteration); // iteration 에 해당하는것 제거. 

/// 제거 . erase
my_vec.erase(my_vec.begin()); // 첫번째 요소 제거 .
my_vec.erase(my_vec.begin()+1); // 2번째 요소 제거 .

my_vec.erase(my_vec.end() - 1); // 마지막것 제거 . -1 해야함. 
my_vec.erase(my_vec.end() - 2); // 마지막 앞에것 제거 . -2 해야함. 

my_vec.erase(iter_start,iter_end); // iter_start 이상 iter_end "미만" 제거. 


- erase(iterator) : 인자 iterator 로 지정된 1개  엘리먼트 삭제. (일반 배열같은 인덱스로 지정안됨)
- erase(it1, it2) it1과 it2 사이의 모든 엘리먼트 삭제. 
- 반환값 : 삭제된 다음 엘리먼트의 iterator

 

 

vector 엘리먼트 메모리 배치는 일반배열과 동일하게 연속 배치됨. 

 

std::vector<double> vec_dbl;


double * p_double = &vec_dbl[0]; // double 포인터로 받음. 아래 data() 로 받는것과 동일. 
double * p_double = vec_dbl.data();// vector 에서 제공되는 함수 이용하여 첫엘리먼트주소받는것. 

 

vector 에서의 비교연산자. 

if(vec1 == vec2)  // 벡터의 모든 요소가 같으면 true. 

if(vec1 != vec2) // 다르다의 정의 : 요소중 1개 이상이 다르면 다른것.

 

vector  assign (다른 vector 복사 ) 

// vec2 의 요소 3~254까지 vec1 에 복사.
vec1.assign (vec2.begin() + 3 , vec2.begin() + 254); 

// vec2 전체요소 를 vec1 에 복사. 
vec1.assign (vec2.begin(), vec2.end());

 

 

vector 최대값, 최소값 , 인덱스 구하기

#include <vector>
#include <algorithm>

std::vector<double> my_vec_double; 

double max = *max_element(my_vec_double.begin(), my_vec_double.end()); // 최대값
int idx_max = max_element(my_vec_double.begin(), my_vec_double.end()); // 최대값인 엘리먼트 인덱스

double min = *min_element(my_vec_double.begin(), my_vec_double.end()); // 최소값
int idx_min = min_element(my_vec_double.begin(), my_vec_double.end()); //최소값인 엘리먼트 인덱스

 

 

 

 

 

연관 

 

 

 

C++. std::map . 키-값 컬렉션

 

 

std::deque .

 

 

 

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첫 등록 : 2016년 1월 20일. 

최종 수정 : 2022.02.05

단축 주소 : https://igotit.tistory.com/570

 

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