The C++ Deque resize method is a built-in function found within the C++ Standard Template Library (STL). Its primary purpose is to adjust the size of the deque container to the specified size provided in the argument, subject to certain conditions.
In C++, programmers frequently use the deque::resize method to adjust the container to a specific number of elements (n). When n exceeds the current container size, new elements are added to expand the container to n elements. Conversely, if n is less than the container size, the container is shrunk to n elements, discarding any elements beyond that limit.
Where n denotes a fresh dimension of the container provided in the parameter.
Syntax
It has the following syntax:
deque<T>.resize(size_type n); // Resize to n, default-initialized
deque<T>.resize(size_type n, const T& val); // Resize to n, filled with val
In this format,
- n stands for a fresh container dimension, which is a required input.
- val denotes a novel value to append within the expanded area.
Return value: It does not return any value.
Resizing a Deque to a Smaller Size Using resize in C++
Let's consider a basic scenario where n is smaller than the size of the container.
Example
#include <iostream>
#include<deque>
using namespace std; //using standard namespace
int main() //main function
{
deque<int> d={100,200,300,400,500};
d.resize(3);
for(int i=0;i<d.size();i++)
{
cout<<d[i];
cout<<" ";
}
return 0;
}
Output:
100 200 300
Explanation:
In this instance, we've established a deque that stores integer values and set it up with specific elements. Subsequently, we have employed the resize method to adjust the container's size to 3, consequently eliminating elements past the third position. Following this, a for loop combined with the size function is utilized to exhibit the remaining deque elements. This displays the initial three elements, affirming the successful resizing of the deque.
C++ Example to Expand a Deque with Default Values Using the resize Function
Let's consider a scenario to demonstrate the process of enlarging a deque with default values by utilizing the resize method in C++.
Example
#include <iostream>
#include<deque>
using namespace std; //using standard namespace
int main() //main function
{
deque<string> d={"C","C++","Java",".Net","Python"};
d.resize(7,"Rust");
for(int i=0;i<d.size();i++)
{
cout<<d[i];
cout<<" ";
}
return 0;
}
Output:
C C++ Java .Net Python Rust Rust
Explanation:
In this instance, we've created a deque with string values and expanded its size to 7 using the resize function. Following that, we've populated the additional positions with the string "Rust". Subsequently, a for loop is employed to showcase all elements within the deque. Ultimately, the deque has grown beyond its initial capacity, with "Rust" filling the newly added slots, resulting in its appearance twice in the output.
C++ deque resize Example to resize an empty deque
Let's consider a scenario to demonstrate the process of adjusting the size of an empty deque by utilizing the resize method in C++.
Example
#include <iostream>
#include <deque>
using namespace std; //using standard namespace
int main() { //main function
deque<int> dq;
dq.resize(6, 15); // Expands empty deque to 4 elements with value 10
cout << "After resize(6, 15): ";
for (int x : dq)
cout << x << " ";
return 0;
}
Output:
After resize(6, 15): 15 15 15 15 15 15
Explanation:
In this instance, a deque was instantiated as empty and then enlarged to accommodate 6 elements via the resize method, with each element set to 15 by default. Subsequently, a range-based for loop was employed to exhibit all elements within the deque, revealing that it currently holds six instances of the value 15.
Features of the deque resize function in C++
There are several features of the deque resize function in C++. Some main features are as follows:
- In the C++ programming language, the deque resize function is commonly used to increase or decrease the number of elements in a deque.
- The resize function takes a constant-time operation (O(1)) when elements are shrunk. On the other hand, it also takes linear (O(n)) time complexity when the number of elements grows.
- It doesn't return any value.
- If we want to increase the deque size, we can easily initialize the element with a specified value.
- If we want to reduce the deque size, we can remove the elements from the end of the deque.
Conclusion
In summary, the C++ deque::resize method is frequently used to modify the element count in a deque container. It has the capability to decrease the deque size by eliminating elements from the end or increase it by adding new elements that are either default-initialized or initialized with a specific value.
The resize method is a valuable tool for dynamically adjusting the size of a deque in C++ according to specific program needs. It operates with constant-time complexity O(1) when reducing the size, but transitions to linear time complexity O(n) when increasing it. In summary, resize is a straightforward yet effective function for managing deque size efficiently.
C++ Deque Resize Function FAQs
The primary objective of the deque::resize function in the C++ programming language is to adjust the size of the deque container.
In C++, the deque::resize method is frequently employed to adjust the quantity of elements stored in the deque container. This function allows for both expansion and contraction of the element count within a deque.
No, the resize function in C++ does not invalidate iterators or references.
Yes, altering the size of a deque can render iterators, references, and pointers invalid, particularly when new memory blocks are assigned during enlargement. When the deque is reduced in size, only iterators and references to the eliminated elements become invalid, while those referencing the remaining elements typically stay intact. Nevertheless, it is advisable to consider that iterators might become invalidated following a resize function.
The deque resize function in C++ may have the following common limitations:
- It may lead to reallocation of memory, impacting performance.
- Resizing a deque may invalidate existing iterators, causing potential issues.
- The resize operation may involve moving elements in memory, leading to overhead.
- Resizing a deque to a smaller size may result in unused memory being retained.
- The complexity of resizing a deque can vary based on the implementation, affecting efficiency.
There are several drawbacks to the deque resize function in C++. Some of them are as follows:
- If we use the resize method without any value, elements get constructed by default, such as 0 for ints, empty for strings.
- If the element type has pointers or resources, ensure proper destructors to avoid leaks during truncation.
- Deques are not thread-safe, concurrent resizes can corrupt the data.
- Resizing an empty deque works fine, but resizing to 0 clears it entirely.
- Repeatedly resizing larger than smaller can fragment memory due to block allocation.
What occurs when the size of the new deque surpasses the size of the existing deque in C++?
If there is a requirement to enlarge the size of a deque in the C++ programming language, the deque resize method can be employed to extend it by appending fresh elements at the deque's conclusion. These additional elements are either default-initialized or initialized with a specific value.
5) Is it possible to employ the resize method with a constant (const) deque in C++?
No, the resize method cannot be used with a const deque since the resize operation alters the content of the container. The resize function requires a deque that is not const.
