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C++ Pointer to Vector: A Guide for Beginners

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C++ Pointer to Vector

In C++, a vector is a dynamic array that can grow and shrink as needed. It is a powerful data structure that is used in a variety of applications, such as data science, machine learning, and game development.

A pointer to a vector is a variable that stores the address of a vector object. This allows you to access the vector object from anywhere in your code. Pointers to vectors can be used to pass vectors to functions, return vectors from functions, and share data between different parts of your code.

In this article, we will discuss the basics of pointers to vectors in C++. We will cover topics such as:

  • Creating pointers to vectors
  • Accessing the elements of a vector through a pointer
  • Passing vectors to functions by reference
  • Returning vectors from functions
  • Sharing data between different parts of your code

By the end of this article, you will have a solid understanding of how to use pointers to vectors in C++.

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| Column 1 | Column 2 | Column 3 | |—|—|—| | Definition | Syntax | Example | | A pointer to a vector is a variable that stores the address of a vector object. | `std::vector *ptr = &vec;` | `int main() { std::vector vec = {1, 2, 3, 4, 5}; std::vector *ptr = &vec;

// Access the elements of the vector using the pointer. for (int i = 0; i < vec.size(); i++) { std::cout << ptr[i] << std::endl; } return 0; }` | | Advantages | Disadvantages | | Pointers to vectors can be used to access the elements of a vector more efficiently than using iterators. | Pointers to vectors can be more difficult to use than iterators. |

A vector is a sequence container that stores elements of the same type in a contiguous block of memory. It is a dynamic array that can grow and shrink as needed. Vectors are one of the most commonly used data structures in C++.

A pointer to a vector is a variable that stores the address of a vector object. It can be used to access the elements of the vector object and to modify its size.

In this tutorial, we will learn how to create, use, and delete pointers to vectors in C++.

What is a pointer to a vector?

The syntax for declaring a pointer to a vector is as follows:

c++ vector * my_vector_pointer;

where `vector ` is the type of the vector object and `my_vector_pointer` is the name of the pointer variable.

How to create a pointer to a vector?

There are two ways to create a pointer to a vector:

  • Directly , by using the `new` operator.
  • Indirectly , by using the `&` operator to get the address of a vector object.

To create a pointer to a vector directly, you can use the `new` operator. The syntax for creating a pointer to a vector directly is as follows:

c++ vector * my_vector_pointer = new vector ();

This code creates a new vector object and stores its address in the pointer variable `my_vector_pointer`.

To create a pointer to a vector indirectly, you can use the `&` operator to get the address of a vector object. The syntax for creating a pointer to a vector indirectly is as follows:

c++ vector my_vector; vector * my_vector_pointer = &my_vector;

This code creates a vector object called `my_vector` and stores its address in the pointer variable `my_vector_pointer`.

How to use a pointer to a vector?

Once you have created a pointer to a vector, you can use it to access the elements of the vector object and to modify its size.

To access an element of a vector, you can use the `[]` operator. The syntax for accessing an element of a vector using a pointer is as follows:

c++ (*my_vector_pointer)[index];

where `my_vector_pointer` is the pointer variable and `index` is the index of the element you want to access.

To modify the size of a vector, you can use the `size()` and `resize()` methods. The syntax for using the `size()` method is as follows:

c++ my_vector_pointer->size();

This method returns the number of elements in the vector object.

The syntax for using the `resize()` method is as follows:

c++ my_vector_pointer->resize(new_size);

This method changes the size of the vector object to `new_size`.

How to delete a pointer to a vector?

To delete a pointer to a vector, you can use the `delete` operator. The syntax for deleting a pointer to a vector is as follows:

c++ delete my_vector_pointer;

where `my_vector_pointer` is the pointer variable.

In this tutorial, we learned how to create, use, and delete pointers to vectors in C++. We also learned how to access the elements of a vector and to modify its size.

Pointers to vectors can be a powerful tool for manipulating data in C++. By understanding how to use them, you can write more efficient and effective code.

3. How to access the elements of a vector using a pointer?

To access the elements of a vector using a pointer, you can use the `->` operator. For example, to access the element at index `i`, you would use the following syntax:

where `ptr` is the pointer to the vector and `i` is the index of the element.

This syntax is similar to the syntax for accessing the elements of an array. However, there are a few important differences. First, a vector is a dynamic array, which means that its size can change at runtime. This means that you cannot always use the array index operator (`[]`) to access the elements of a vector. Second, a vector is a reference type, which means that when you pass a vector to a function, you are passing a reference to the vector, not a copy of the vector. This means that any changes that you make to the vector inside the function will be reflected in the original vector.

For these reasons, it is generally recommended to use the `->` operator to access the elements of a vector. This will ensure that you are always accessing the correct elements of the vector, and that any changes that you make to the vector will be reflected in the original vector.

Here is an example of how to use the `->` operator to access the elements of a vector:

c++ include include

using namespace std;

int main() { // Create a vector of integers. vector numbers = {1, 2, 3, 4, 5};

4. How to modify the size of a vector using a pointer?

To modify the size of a vector using a pointer, you can use the `resize()` method. The `resize()` method takes two arguments: the new size of the vector and a boolean value that specifies whether to fill the new elements with default values.

The following code shows how to use the `resize()` method to modify the size of a vector:

// Resize the vector to a size of 10. numbers.resize(10, 0);

5. How to iterate over a vector using a pointer?

To iterate over a vector using a pointer, you can use the `for` loop. The following code shows how to iterate over a vector of integers using a pointer:

// Iterate over the vector using a pointer. for (int* i = numbers.data(); i < numbers.data() + numbers.size(); i++) { cout << *i << endl; } return 0; } Output: 1 2 3 4 5 Note that the `data()` method returns a pointer to the

Q: What is a pointer to a vector in C++?

Q: How do I create a pointer to a vector in C++?

To create a pointer to a vector, you can use the following syntax:

c++ vector *pVector = new vector ();

This creates a pointer to a vector of integers. You can then use the pointer to access the elements of the vector and to modify its size.

Q: How do I access the elements of a vector using a pointer?

To access the elements of a vector using a pointer, you can use the following syntax:

c++ (*pVector)[index]

This expression will return the element at the specified index of the vector.

Q: How do I modify the size of a vector using a pointer?

To modify the size of a vector using a pointer, you can use the following syntax:

c++ pVector->resize(newSize);

This will resize the vector to the specified size.

Q: What are the advantages of using a pointer to a vector?

There are several advantages to using a pointer to a vector. First, it allows you to access the elements of the vector without having to dereference the pointer. This can be more efficient, especially when you are accessing the elements of the vector multiple times. Second, it allows you to modify the size of the vector without having to create a new vector object. This can be more efficient, especially when you are frequently resizing the vector.

Q: What are the disadvantages of using a pointer to a vector?

There are two main disadvantages to using a pointer to a vector. First, it can be more difficult to debug code that uses pointers than code that does not. Second, pointers can be dangerous if they are not used correctly. If you accidentally dereference a null pointer, your program will crash.

Q: When should I use a pointer to a vector?

You should use a pointer to a vector when you need to access the elements of the vector without having to dereference the pointer, when you need to modify the size of the vector, or when you are working with code that uses pointers.

Q: What are some common errors that can occur when using pointers to vectors?

The most common errors that can occur when using pointers to vectors are:

  • Dereferencing a null pointer: This will cause your program to crash.
  • Modifying the size of a vector through a pointer that is not pointing to the vector: This will cause your program to crash.
  • Passing a pointer to a vector to a function that expects a reference to a vector: This will cause your program to crash.

Q: How can I avoid these errors?

To avoid these errors, you should:

  • Always check to make sure that a pointer is not null before dereferencing it.
  • Always make sure that you are modifying the size of the vector through a pointer that is pointing to the vector.
  • Always pass a pointer to a vector to a function that expects a reference to a vector.

By following these tips, you can avoid the most common errors that can occur when using pointers to vectors.

In this blog post, we have discussed the concept of a C++ pointer to vector. We have seen how to declare, initialize, and use a pointer to vector. We have also seen how to pass a vector to a function by reference and by pointer. Finally, we have discussed the pros and cons of using pointers to vectors.

Here are some key takeaways from this blog post:

  • A pointer to vector is a variable that stores the address of a vector.
  • To declare a pointer to vector, use the `std::vector *` type.
  • To initialize a pointer to vector, use the `new` operator.
  • To use a pointer to vector, dereference it using the `->` operator.
  • You can pass a vector to a function by reference or by pointer.
  • Passing a vector by reference is more efficient than passing it by pointer.
  • Using pointers to vectors can lead to memory leaks and behavior.

Overall, pointers to vectors can be a powerful tool for C++ programmers. However, it is important to use them carefully to avoid potential problems.

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std::vector assign() method

  • since C++20
  • since C++11
  • until C++11

Replaces the contents of the container with the contents of another.

(1) Replaces the contents with count copies of value value .

(2) Replaces the contents with copies of those in the range [ first, last ) .

The behavior is undefined

This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator .

This overload has the same effect as overload (1) if InputIt is an integral type.

(3) Replaces the contents with the elements from the initializer list ilist .

All iterators , pointers and references to the elements of the container are invalidated. The past-the-end iterator is also invalidated.

Parameters ​

  • count - the new size of the container
  • value - the value to initialize elements of the container with
  • first , last - the range to copy the elements from
  • ilist - initializer list to copy the values from

Return value ​

Complexity ​.

  • (1) Linear in count - O(count) .
  • (2) Linear in distance between first and last - O(std::distance(firs,t last)) .
  • (3) Linear in ilist.size() - O(ilist.size()) .

Exceptions ​

  • Return value

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Std::vector<t,allocator>:: vector.

(C++20)
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(C++20)
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vector::cbegin (C++11)
vector::cend (C++11)
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)

operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
erase_if(std::vector) (C++20)




(1)
); (until C++17)
) noexcept(noexcept(Allocator())); (since C++17)
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(2)
vector( const Allocator& alloc ); (until C++17)
vector( const Allocator& alloc ) noexcept; (since C++17)
(constexpr since C++20)
(3)
vector( size_type count,

                 const T& value = T(),

                 const Allocator& alloc = Allocator() );
(until C++11)
size_type count,

        const T& value,

        const Allocator& alloc = Allocator() );
(since C++11)
(constexpr since C++20)
(4)
vector( size_type count ); (since C++11)
(until C++14)
vector( size_type count,
                 const Allocator& alloc = Allocator() );
(since C++14)
< class InputIt >

vector( InputIt first, InputIt last,

        const Allocator& alloc = Allocator() );
(5) (constexpr since C++20)
const vector& other ); (6) (constexpr since C++20)
const vector& other, const Allocator& alloc ); (7) (since C++11)
(constexpr since C++20)
vector&& other ); (8) (since C++11)
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(10) (since C++11)
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template< <T> R >

constexpr vector( , R&& rg,

                  const Allocator& alloc = Allocator() );
(11) (since C++23)

Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc .

This constructor has the same effect as vector(static_cast<size_type>(first), static_cast<value_type>(last), a) if is an integral type.

(until C++11)

This overload participates in overload resolution only if satisfies , to avoid ambiguity with the overload (3).

(since C++11)

The allocator is obtained as if by calling <allocator_type>::select_on_container_copy_construction(
    other.get_allocator()).

(since C++11)

During , only the first argument contributes to the deduction of the container's template parameter.

(since C++23)
Parameters Complexity Exceptions Notes Example Defect reports See also

[ edit ] Parameters

alloc - allocator to use for all memory allocations of this container
count - the size of the container
value - the value to initialize elements of the container with
first, last - the range first last to copy the elements from
other - another container to be used as source to initialize the elements of the container with
init - initializer list to initialize the elements of the container with
rg - a , that is, an whose elements are convertible to

[ edit ] Complexity

  • If first and last are both forward, bidirectional or random-access iterators,
  • The copy constructor of T is only called N   times, and
  • No reallocation occurs.
  • Otherwise ( first and last are just input iterators),
  • The copy constructor of T is called O(N) times, and
  • Reallocation occurs O(log N) times.
  • If R models ranges::forward_range or ranges::sized_range ,
  • Initializes exactly N elements from the result of dereferencing successive iterators of rg , and
  • Otherwise ( R models input range),
  • The copy or move constructor of T is called O(N) times, and

[ edit ] Exceptions

Calls to Allocator :: allocate may throw.

[ edit ] Notes

After container move construction (overload (8) ), references, pointers, and iterators (other than the end iterator) to other remain valid, but refer to elements that are now in * this . The current standard makes this guarantee via the blanket statement in [container.reqmts]/67 , and a more direct guarantee is under consideration via LWG issue 2321 .

The overload (4) zeroes out elements of non-class types such as int , which is different from the behavior of new[] , which leaves them uninitialized. To match the behavior of new [ ] , a custom Allocator::construct can be provided which leaves such elements uninitialized.

Note that the presence of list-initializing constructor (10) means list initialization and direct initialization do different things:

macro Value Std Feature
202202L (C++23) construction and insertion; overload ( )

[ edit ] Example

[ edit ] defect reports.

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
C++98 overload (5) allowed up to 2N  copy
constructor calls in the input iterator case
changed to O(N) calls
C++98 for overload (4), the elements in the container were default constructed they are value-initialized
C++11 the default constructor is explicit made non-explicit

[ edit ] See also

assigns values to the container
(public member function)
assigns values to the container
(public member function)
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6.4. Storing Pointers in a vector

For efficiency or other reasons, you can’t store copies of your objects in a vector , but you need to keep track of them somehow.

Store pointers to your objects in a vector instead of copies of the objects themselves. But if you do, don’t forget to delete the objects that are pointed to, because the vector won’t do it for you. Example 6-4 shows how to declare and work with vector s of pointers.

Example 6-4. Using vectors of pointers

You can store pointers in a vector just like you would anything else. Declare a vector of pointers like this:

The important thing to remember is that a vector stores values without regard for what those values represent. It, therefore, doesn’t know that it’s supposed to delete pointer values when it’s destroyed. If you allocate memory, then put pointers to that ...

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vector assign from pointer

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  Pointer to a vector

vector assign from pointer

vector < > ints_t; ints_t* i_am_a_pointer_to_a_vector;
> A, B, C; vector< >::pointer X = A
std; print( vector < > * v ) { ( n = 0; n < v->size(); n++) cout << v->at( n ) << ; cout << endl; } main() { _primes[] = { 2, 3, 5, 7 }; _fibonaccis[] = { 1, 1, 2, 3 }; vector < > primes( _primes, _primes + 4 ); vector < > fibonaccis( _fibonaccis, _fibonaccis + 4 ); print( &primes ); print( &fibonaccis ); 0; }

<vector>

Std:: vector ::assign.

range (1)
fill (2)
range (1)
fill (2)
initializer list (3)

Return value

main () { std::vector< > first; std::vector< > second; std::vector< > third; first.assign (7,100); std::vector< >::iterator it; it=first.begin()+1; second.assign (it,first.end()-1); myints[] = {1776,7,4}; third.assign (myints,myints+3); std::cout << << (first.size()) << ; std::cout << << (second.size()) << ; std::cout << << (third.size()) << ; 0; }

Iterator validity

Exception safety.

  • Information
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  • <cctype> (ctype.h)
  • <cerrno> (errno.h)
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  • <cfloat> (float.h)
  • <cinttypes> (inttypes.h)
  • <ciso646> (iso646.h)
  • <climits> (limits.h)
  • <clocale> (locale.h)
  • <cmath> (math.h)
  • <csetjmp> (setjmp.h)
  • <csignal> (signal.h)
  • <cstdarg> (stdarg.h)
  • <cstdbool> (stdbool.h)
  • <cstddef> (stddef.h)
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  • <cstdio> (stdio.h)
  • <cstdlib> (stdlib.h)
  • <cstring> (string.h)
  • <ctgmath> (tgmath.h)
  • <ctime> (time.h)
  • <cuchar> (uchar.h)
  • <cwchar> (wchar.h)
  • <cwctype> (wctype.h)

Containers:

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  • <unordered_set>

Input/Output:

  • <fstream>
  • <iomanip>
  • <ios>
  • <iosfwd>
  • <iostream>
  • <istream>
  • <ostream>
  • <sstream>
  • <streambuf>

Multi-threading:

  • <atomic>
  • <condition_variable>
  • <future>
  • <mutex>
  • <thread>
  • <algorithm>
  • <bitset>
  • <chrono>
  • <codecvt>
  • <complex>
  • <exception>
  • <functional>
  • <initializer_list>
  • <iterator>
  • <limits>
  • <locale>
  • <memory>
  • <new>
  • <numeric>
  • <random>
  • <ratio>
  • <regex>
  • <stdexcept>
  • <string>
  • <system_error>
  • <tuple>
  • <typeindex>
  • <typeinfo>
  • <type_traits>
  • <utility>
  • <valarray>
  • vector<bool>
  • vector::vector
  • vector::~vector

member functions:

  • vector::assign
  • vector::back
  • vector::begin
  • vector::capacity
  • vector::cbegin
  • vector::cend
  • vector::clear
  • vector::crbegin
  • vector::crend
  • vector::data
  • vector::emplace
  • vector::emplace_back
  • vector::empty
  • vector::end
  • vector::erase
  • vector::front
  • vector::get_allocator
  • vector::insert
  • vector::max_size
  • vector::operator=
  • vector::operator[]
  • vector::pop_back
  • vector::push_back
  • vector::rbegin
  • vector::rend
  • vector::reserve
  • vector::resize
  • vector::shrink_to_fit
  • vector::size
  • vector::swap

non-member overloads:

  • relational operators (vector)
  • swap (vector)

How to Create Vector of Pointers in C++

  • How to Create Vector of Pointers in C++

Use [] Notation to Create Vector of Pointers in C++

Use the new operator to create vector of pointers on dynamic memory in c++, use the std::vector container to create vector of pointers in c++.

How to Create Vector of Pointers in C++

This article will explain several methods of how to create a vector of pointers in C++.

Since the pointer types can be modified easily, we will use int * in the following examples to declare a vector of pointers. Alternatively, we can use the void * pointer if you require a generic address type to store opaque data structures or, on the contrary, use a pointer to a custom defined class.

This solution uses a C-style array notation - [] that declares a fixed-length array. It is similar to the regular array declaration, but in this case, we are interested in accessing each element’s addresses. We are using the & (address of) operator to access pointers in the vector and print them out to the console. Note that these memory addresses are located on the stack memory.

On the other hand, we can utilize the new operator to create a vector of pointers dynamically allocated on the heap.

This solution requires the programmer to free up the memory before the program exits; otherwise, the code will suffer from the memory leak, which can be a massive problem in long-running applications and resource-constrained hardware environments. Note that we use the delete [] notation to clean up each location in a dynamically allocated vector.

std::vector offers rich functionality to allocate a vector of pointers and manipulate the vector with multiple built-in functions. This method provides a more flexible interface for new element creation during the run-time. Notice that we initialized the vector elements with the nullptr value, as shown in the following example.

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Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

Related Article - C++ Pointer

  • Dangling Pointers in C++
  • Declaration and Uses of unique_ptr in C++
  • Function Pointer to Member Function in C++
  • How to Swap Two Numbers Using Pointers in C++
  • Void Pointer in C++
  • Functionality and Difference Between *& and **& in C++
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Assigning a value to a pointer

If I have the following for example:

For the statement: x = func(a); , do we say that we are returning an address to x ? Or, how exactly do we read it?

EDIT : Is it eligible to say that we are returning a pointer to x ? If so, can you explain how this is done exactly? I mean, how are we returning a pointer?

Lightness Races in Orbit's user avatar

7 Answers 7

x is a pointer to an int , so in other words it is the address of a memory location where an int is stored. So x = func(a) means that func returns the address of an int and stores it in the variable x .

Take care not to return the address of a local variable whose contents would be undefined after func returns.

Alexander Gessler's user avatar

RE: Your edit:

EDIT: Is it eligible to say that we are returning a pointer to x? If so, can you explain how is this done exactly? I mean, how are we returning a pointer?

Yes, it is certainly eligible. Try and think of and treat pointers as any other data type. Under the hood, they are just memory addresses. A pointer can be returned the same way any other data type can be returned.

Take this code for example:

Say that "y" is declared globally as: "int* y = ...". Now the memory address being pointed to by "x" is the same as the memory address being pointed to by "y".

Now let's say that "y" was -not- declared as a pointer, but instead as a normal int (e.g. "int y = 5"). The function could do this and still be valid:

AlexFZ's user avatar

*x is points to int typed variable in memory. So function func should return address to int.

For example the getGlobalCounter function:

But isn't always good idea to delete objects returned from functions. In that case it should result in runtime error, because of counter isn't dynamically allocated int as in top example.

kravemir's user avatar

If you are assigning a variable's value to the return-type of a function, then that return-type must match the variable's type. This goes the same for pointers.

So, if you have:

Then setting myPointer equal to func() will change the memory address which "myPointer" points to, to the memory address returned by func().

x is a pointer, specifically to an int. So it should be obvious that there are two memory locations used. One for the pointer and one for the memory it's pointing to (assuming the pointer is not null).

The pointer itself holds a memory address, specifically the location of the memory it's pointing to. Something like 0xa456e4fa.

Yes, func() is returning a pointer. The prototype of func would look like the following..

Notice the return type is a pointer to an int. From this and what I said previously, it should be obvious what this will return. Something of the form 0xyyyyyy, or a memory address/pointer. That memory address goes into your x pointer.

Remember that the pointer itself is not holding the data that it's pointing to, it is only the address. There's really no reason you CAN'T return a pointer. However, you do need to be careful in WHAT you return. You do not want to return the address of a local variable because that variable will go out of scope once the function has completed its execution. You'll then be returning the address of something invalid. Returning the VALUE of a local pointer however, is fine because the value you returned (the address) will be preserved as will the memory it's pointing to.

I also just realized I wrote you a book. Damn, I sure do ramble when I'm tired.

MGZero's user avatar

The statement just reads that x is assigned the value returned by function func . For the code to compile without errors , the func should return an address though . And for the code to execute as expected as AlexFZ pointed out , you should take care that func does not return the address of a variable local to the function.

woodstok's user avatar

It means that func() returns a variable of type int*.

Is it eligible to say that we are returning a pointer to x?

No, we are returning a pointer to an integer and assigning it to x since it is a pointer.

This is an example code which returns an int pointer int* func(int a) { int *y = &a; return y; }

cppcoder's user avatar

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vector assign from pointer

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Different Ways to Convert Vector to Array in C++ STL

An array is the collection of data belonging to a primitive data type. The data in this is kept in a continuous memory location. Vectors are dynamic arrays that can be resized to meet the needs. We can convert vectors to arrays in the following ways given below.

Input : Vector: [1, 2, 3, 4, 5] Output: Array: [1, 2, 3, 4, 5] Input : Vector: [‘G’, ‘e’, ‘e’, ‘k’, ‘s’]  Output: Array: [‘G’, ‘e’, ‘e’, ‘k’, ‘s’] 

Here, we will discuss the 5 ways to convert Vector to Array in C++ STL:

  • Naive Approach to Convert Vector to Array
  • Using copy() function in C++ STL
  • Using transform() function in C++ STL
  • Using data() function in C++ STL
  • Using & operator in C++

1. Naive Approach to Convert Vector to Array

The vector can be converted to an array by first allocating the array’s memory sufficient to accommodate all vector elements. Then we run a for loop and copy every element of the vector to the array.

       

Time Complexity: O(n) Auxiliary Space: O(n)

2. Using copy() function in C++ STL

copy() function in C++ is used to copy a range of elements from one container to another. It takes 3 arguments which are a pointer to the beginning of the source container, a pointer to the end of the source container, and a pointer to the beginning of the destination container.

         

3. Using transform() function in C++ STL

transform() function in C++ is used to copy a range of elements from one container to another based upon a unary operation. It takes 4 parameters which include a pointer to the beginning of the source container, a pointer to the end of the source container, and a pointer to the beginning of the destination container, a unary operation.

4. Using data() function in C++ STL

data() function in C++ returns a pointer to the first element in the array which is used internally by the vector. There are no parameters accepted by this function.

Time Complexity: O(n) Auxiliary Space: O(1)

Note: Be aware that in case of STL SequenceContainers which can change their size at runtime, like std::vector, there is no guarantee that the memory location of the underlying array will stay same across container manipulations that change the containers size.

5. Using & operator in C++

When used on the first element of an STL SequenceContainer (std::vector, std::array…), the & operator returns a pointer to the first element of an internally used C-style array. That array can be accessed and modified directly. 

       

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  1. c++

    1. Yep. You should be able to do this. The relevant constructor is template <class InputIterator> vector ( InputIterator first, InputIterator last, const Allocator& = Allocator() ); - and pointers are iterators too (since you can do integer arithmetic on them). That being said, all that the vector is doing is iterating over the elements of d ...

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  3. std::vector<T,Allocator>::assign

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  4. vector

    Assign vector content Assigns new contents to the vector , replacing its current contents, and modifying its size accordingly. In the range version (1), the new contents are elements constructed from each of the elements in the range between first and last , in the same order.

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  6. vector

    Allows direct access to any element in the sequence, even through pointer arithmetics, and provides relatively fast addition/removal of elements at the end of the sequence. ... assign Assign vector content (public member function) push_back Add element at the end (public member function) pop_back Delete last element (public member function) insert

  7. vector<...>::assign() method

    std::vector assign () method. Replaces the contents of the container with the contents of another. (1) Replaces the contents with count copies of value value. (2) Replaces the contents with copies of those in the range [ first, last ).

  8. vector :: assign() in C++ STL

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  9. std::vector

    2)std::pmr::vector is an alias template that uses a polymorphic allocator. The elements are stored contiguously, which means that elements can be accessed not only through iterators, but also using offsets to regular pointers to elements. This means that a pointer to an element of a vector may be passed to any function that expects a pointer to ...

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    constexpr vector (std::from_range_t, R && rg, const Allocator& alloc = Allocator()); (11) (since C++23) Constructs a new container from a variety of data sources, optionally using a user supplied allocator alloc . 1) Default constructor. Constructs an empty container with a default-constructed allocator. 2) Constructs an empty container with ...

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  15. vector::assign

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  20. c++

    Notice the return type is a pointer to an int. From this and what I said previously, it should be obvious what this will return. Something of the form 0xyyyyyy, or a memory address/pointer. That memory address goes into your x pointer. Remember that the pointer itself is not holding the data that it's pointing to, it is only the address.

  21. Different Ways to Convert Vector to Array in C++ STL

    Here, we will discuss the 5 ways to convert Vector to Array in C++ STL: 1. Naive Approach to Convert Vector to Array. The vector can be converted to an array by first allocating the array's memory sufficient to accommodate all vector elements. Then we run a for loop and copy every element of the vector to the array.