Tips on using STL containers

STL (Standard Template Library) is a very commonly used standard library in C, which contains many containers, such as vector, map, set, etc. These containers are widely used in C development and have the advantages of high efficiency and ease of use. However, in actual use, we also need some skills to better use these containers. This article will introduce some tips for using STL containers.

1. Tips for using vector containers

Vector is one of the most commonly used STL containers. It can implement dynamic arrays, similar to ArrayList in Java. However, you need to pay attention to the following points when using it:

1. Avoid using push_back and pop_back

Although push_back and pop_back are the most basic operations of vector, they are used when inserting or deleting elements. Very time consuming. push_back needs to reallocate space and copy data; pop_back needs to destruct the tail elements. Therefore, it is generally recommended to use the reserve function to allocate space first, and then use subscripts to access elements.

2. Use the emplace_back function

The emplace_back function can directly insert elements at the end of the vector, which is more efficient than push_back. Moreover, emplace_back can also pass parameters to construct elements, which can reduce unnecessary copy construction.

3. Use the swap function to delete elements

vector Deleting elements requires moving subsequent elements to fill the gaps. Therefore, when deleting elements, you can consider using the swap function to swap the element to be deleted with the last element, and then pop_back. This can reduce the number of element moves and improve efficiency.

2. Tips for using map containers

Map is an ordered associative container in which the elements are sorted according to key values. When using map, you can consider the following points:

1. Use iterator to traverse

Because map is ordered, using iterator to traverse can ensure that the traversal order is consistent with the key value. sequence.

2. Use lower_bound and upper_bound functions to search

The lower_bound and upper_bound functions can quickly search in an ordered container and return an iterator. lower_bound returns an iterator of the smallest element greater than or equal to a certain value, and upper_bound returns an iterator of the smallest element greater than a certain value.

3. Use the find function to search

Using the find function can quickly search, but it should be noted that if the element does not exist, the iterator returned by find will point to the end of the container. Therefore, you need to use the count function to determine whether the element exists before using find.

3. Tips for using set containers

set is also an ordered associative container, in which the elements are sorted according to key values. When using set, you can consider the following points:

1. Use the emplace function to insert elements

The insertion function emplace of set can directly insert elements, which is more efficient than the insert function, and can pass parameters Construction elements.

2. Use the find function to search

Using the find function can quickly search, but it should be noted that if the element does not exist, the iterator returned by find will point to the end of the container. Therefore, you need to use the count function to determine whether the element exists before using find.

3. Use lower_bound and upper_bound functions to search

The lower_bound and upper_bound functions can quickly search in an ordered container and return an iterator. lower_bound returns an iterator of the smallest element greater than or equal to a certain value, and upper_bound returns an iterator of the smallest element greater than a certain value.

To sum up, the tips for using STL containers involve avoiding some inefficient operations while utilizing some efficient functions. These techniques can improve the efficiency and quality of STL containers to a certain extent, making development more efficient.

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