How to replace elements in C++ STL container?

The method of replacing elements in an STL container is as follows: std::vector: use at() or [] operator; std::list: access elements through iterator; std::map and std::unordered_map: use [ ] operator.

How to replace elements in C++ STL containers

In the C++ Standard Template Library (STL), there are various containers that can store and manipulate elements. Replacing an element at a specific location in a container is a common task. Here's how to replace elements in different STL container types:

1. Replace elements in std::vector

for std::vector, specific elements can be accessed and modified using the at() or [] operators.

// 使用 at()
std::vector<int> vec{1, 2, 3, 4, 5};
vec.at(2) = 10; // 替换 vec[2] 为 10

// 使用 []
vec[3] = 20; // 替换 vec[3] 为 20

2. Replace elements in std::list

For std::list, you can useiterator Access and modify elements.

std::list<std::string> lst{"a", "b", "c", "d", "e"};
auto it = std::next(lst.begin(), 2); // 迭代器指向 lst[2]
*it = "z"; // 替换 lst[2] 为 "z"

3. Replace elements in std::map and

std::unordered_map

for std::map and std::unordered_map, you can use the [] operator to access and modify specific elements.

// std::map
std::map<std::string, int> mp{ {"a", 1}, {"b", 2}, {"c", 3} };
mp["a"] = 10; // 替换 mp["a"] 为 10

// std::unordered_map
std::unordered_map<std::string, int> ump{ {"a", 1}, {"b", 2}, {"c", 3} };
ump["a"] = 10; // 替换 ump["a"] 为 10

Practical case

Suppose we have a std::vector, which stores the names of students, and we need to reorder them in alphabetical order Name. We can use STL's std::sort() function to sort the container, and the at() function to replace elements to match the sorted order.

std::vector<std::string> names{"John", "Alice", "Bob", "Mary", "David"};
std::sort(names.begin(), names.end());

for (int i = 0; i < names.size(); ++i) {
    names.at(i) = std::to_string(i + 1) + ". " + names[i];
}

In this example, we sort the names container, then iterate through the elements one by one and replace them with the modified string, including the position and name. The end result is an alphabetical list of names, preceded by their rank.

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