Emplace vs push mail

A question that gets to the heart of C++'s container classes!

emplace and push_back are two different ways to add elements to a container, such as a std::vector or std::list. While they may seem similar, they have distinct differences in terms of behavior and performance.

push_back

push_back is a member function of the container class that adds a new element to the end of the container. It takes a single argument, which is the value to be added. Here's an example:

std::vector<int> vec;
vec.push_back(42);

When you call push_back, the container creates a new element and copies the value into it. This means that the element is constructed in the container, and then the value is copied into it.

emplace_back

emplace_back is a member function of the container class that adds a new element to the end of the container. It takes a variable number of arguments, which are used to construct the new element in-place. Here's an example:

std::vector<int> vec;
vec.emplace_back(42);

When you call emplace_back, the container constructs the new element in-place, using the arguments provided. This means that the element is constructed directly in the container, without the need for a copy.

Key differences

Here are the key differences between push_back and emplace_back:

1. Copy vs. Move: push_back creates a copy of the value, while emplace_back constructs the element in-place, using the arguments provided.
2. Performance: emplace_back is generally faster than push_back, since it avoids the overhead of creating a copy.
3. Return value: push_back returns a reference to the container, while emplace_back returns a void (i.e., no return value).

When to use each

Here are some guidelines on when to use each:

• Use push_back when you need to add a value to a container and don't care about the performance implications.
• Use emplace_back when you need to add a value to a container and want to avoid the overhead of creating a copy. This is particularly important when working with large or complex objects.

In summary, push_back creates a copy of the value and adds it to the container, while emplace_back constructs the element in-place, using the arguments provided. Choose the right one based on your specific use case and performance requirements.