Key takeaways
Vector: Vectors are dynamic arrays that can grow in size, offering more flexibility than static arrays.
Iteration methods:
Range-based for loops (C++11+) simplify iteration and are ideal for read-only access.
Traditional
forloop and indexes are useful for index-based operations.Use
iteratorfor fine-grained control.Use the
autokeyword to reduce type errors.Use constant iterators (
cbegin()andcend()) to ensure that elements are not modified.Practical applications: Iteration techniques can be used in data analysis, game development, packet processing, etc.
Understanding how to iterate over a vector is a key skill in the C++ programming language. It has multiple practical applications across various domains. Here are some practical examples of iterating over a vector.
Data analysis: Iterating vector of age data to calculate averages.
Game development: Iterating vector of game objects to apply updates or changes.
Searching: Iterating vector of elements to find specific items.
Packet processing: Iterating vector of network packets to handle or process them.
The Standard Library offers multiple containers for C++ programming, including arrays, vectors, and lists. This library simplifies code, enhances clarity and performance, and reduces maintenance issues. As Bjarne Stroustrup, the creator of C++, acknowledges:
“The standard library saves programmers from having to reinvent the wheel.”
Vectors is one of the useful data structures in C++ that act like dynamic one-dimensional arrays.
vector<int> vec = {1, 2, 3, 4, 5};
In this Answer, we’ll explore five different methods to iterate through a vector in C++, as listed below:
Use a range-based for loop (C++11 and later).
Use a traditional C++ for loop and indexing.
Use an iterator.
Use the auto keyword.
Use a C++ for loop with cbegin() and cend() .
for loop (C++11 and later)Range-based for loops were introduced in C++11, which simplifies the syntax by abstracting away the need for manual indexing or iterators used by traditional for loops.
#include <iostream>#include <vector>using namespace std;int main() {// Declaration of int vectorvector<int> vec = {1, 2, 3, 4, 5};// Corrected range-based for loopfor (int num : vec) {cout << num << " ";}cout << std::endl;return 0;}
for loop and indexingIn C++, vectors can be indexed with []operator, similar to arrays. To iterate through the vector, run a for loop from i = 0 to i = vec.size().
#include <iostream>#include <vector>using namespace std;int main(){//Declaration of int vectorvector<int> vec = {1, 2, 3, 4, 5};// Returns length of vector as unsigned intunsigned int vecSize = vec.size();// Run for loop from 0 to vecSizefor(unsigned int i = 0; i < vecSize; i++){cout << vec[i] << " ";}cout << endl;return 0;}
Note: Instead of the
[]operator, theat()function can also be used to fetch the value of a vector at a specific index:vec.at(i)
- Where
iis the index.
iteratorAn iterator can be generated to traverse through a vector.
vector<int>::iterator iter;
An iterator is used as a pointer to iterate through a sequence, such as a string or vector. The pointer can then be incremented to access the next element in the sequence. To access the value in the memory space to which the iterator is pointing, you must use *.
#include <iostream>#include <vector>using namespace std;int main(){//Declaration of int vectorvector<int> vec = {1, 2, 3, 4, 5};int vecSize = vec.size(); // returns length of vector//Declaration of vector iteratorvector<int>::iterator iter = vec.begin();cout << "Vector: ";// Run for loop from 0 to vecSizefor(iter; iter < vec.end(); iter++){// Access value in the memory to which the pointer// is referencingcout << *iter << " ";}cout << endl;return 0;}
auto keywordThe C++ auto keyword can also be used to traverse through a vector. auto must be given a variable to store the accessed element and the sequence that needs to be iterated. It must be used in conjunction with a for loop, as shown below.
#include <iostream>#include <vector>using namespace std;int main() {//Declaration of int vectorvector<int> vec = {1, 2, 3, 4, 5};int vecSize = vec.size(); // Returns length of vectorcout << "Vector: ";for (auto & element : vec){cout << element << " ";}return 0;}
for loop with cbegin() and cend() cbegin() and cend() are constant iterators that point to constant content. They cannot write to the element that the const element points to, but they can read from it.
cbegin() is a const iterator that points to the first element in the vector and cend() points to the
#include <iostream>#include <vector>using namespace std;int main() {//Declaration of int vectorvector<int> vec = {1, 2, 3, 4, 5};cout << "Vector: ";// Iterating with cbegin() and cend()for (auto it = vec.cbegin(); it != vec.cend(); ++it) {std::cout << *it << " ";}return 0;}
Quiz!
How to access an element using an iterator
it()
it[]
*it
it->
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