How to iterate over a C++ STL container?

To traverse an STL container, you can use the container's begin() and end() functions to obtain the iterator range: Vector: Use a for loop to traverse the iterator range. Linked list: Use the next() member function to traverse the elements of the linked list. Mapping: Get an iterator of key-value pairs and use a for loop to traverse.

How to traverse C++ STL containers

Traversing C++ Standard Template Library (STL) containers is essential in programmers’ daily work a task. STL provides a series of predefined data structures such as vectors, linked lists, and maps, each with its own traversal methods.

Traverse STL vectors

To traverse a vector, we can use the begin() and end() functions to obtain the iterator range:

#include <vector>

int main() {
  std::vector<int> v = {1, 2, 3, 4, 5};

  // 使用基于范围的 for 循环
  for (int num : v) {
    std::cout << num << " ";
  }

  std::cout << std::endl;

  // 使用迭代器
  for (std::vector<int>::iterator it = v.begin(); it != v.end(); ++it) {
    std::cout << *it << " ";
  }

  std::cout << std::endl;

  return 0;
}

Output:

1 2 3 4 5 
1 2 3 4 5 

Traversing STL linked list

To traverse a linked list, we can use the front() and# of the linked list ##back() function and the next() member function of the linked list:

#include <list>

int main() {
  std::list<int> l = {1, 2, 3, 4, 5};

  // 使用基于范围的 for 循环
  for (int num : l) {
    std::cout << num << " ";
  }

  std::cout << std::endl;

  // 使用迭代器
  std::list<int>::iterator it = l.begin();
  while (it != l.end()) {
    std::cout << *it << " ";
    it = it->next();
  }

  std::cout << std::endl;

  return 0;
}

Output:

1 2 3 4 5 
1 2 3 4 5 

Traverse the STL mapping

To iterate over a map, we can use the map's

begin() and end() functions to get an iterator of key-value pairs:

#include <map>

int main() {
  std::map<std::string, int> m = {{"Apple", 1}, {"Banana", 2}, {"Cherry", 3}};

  // 使用基于范围的 for 循环
  for (auto const& [key, value] : m) {
    std::cout << key << ": " << value << std::endl;
  }

  std::cout << std::endl;

  // 使用迭代器
  for (std::map<std::string, int>::iterator it = m.begin(); it != m.end(); ++it) {
    std::cout << it->first << ": " << it->second << std::endl;
  }

  return 0;
}

Output:

Apple: 1
Banana: 2
Cherry: 3

Apple: 1
Banana: 2
Cherry: 3

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