In modern C++, vector literals allow us to initialize std::vector objects using a more concise and intuitive syntax. However, the standard C++ library does not provide built-in support for vector literals. In this blog post, we will explore how to create our own custom vector literals in C++.
What are Vector Literals?
Vector literals are a way to initialize a vector object with a list of elements using a syntax similar to array literals. Instead of explicitly calling the vector’s constructor and passing individual elements, we can use a shorthand syntax to define the elements directly.
For example, with vector literals, we can initialize a vector of integers like this:
std::vector<int> numbers = {1, 2, 3, 4, 5};
Creating Custom Vector Literals
To create our own custom vector literals, we can leverage user-defined literals in C++. User-defined literals allow us to define our own suffix for literals of specific types, including vectors.
Here’s an example of creating a user-defined literal for std::vector<int>:
#include <vector>
std::vector<int> operator"" _vec(const char* str, std::size_t size) {
std::vector<int> result;
// Parse the input literal string and populate the vector
// You can customize the parsing logic according to your needs
return result;
}
In the above code, we define an operator function operator"" _vec which takes a string literal as input and returns a std::vector<int>. The _vec suffix is the custom suffix we choose for our vector literals. The function body is where we parse the input string and populate the vector accordingly.
To use our custom vector literal, we can simply append the _vec suffix to our vector literals as follows:
std::vector<int> numbers = "1 2 3 4 5"_vec;
Here, the string "1 2 3 4 5" is the vector literal, and the suffix _vec indicates that it should be interpreted as a std::vector<int> object.
Example Implementation
Let’s provide a concrete implementation of the parsing logic in our operator function. In this example, we will use space-separated numbers as our vector literal format. We will parse the input string and populate the vector accordingly:
#include <vector>
#include <sstream>
#include <string>
std::vector<int> operator"" _vec(const char* str, std::size_t size) {
std::vector<int> result;
std::istringstream iss(std::string(str, size));
int number;
while (iss >> number) {
result.push_back(number);
}
return result;
}
With this implementation, we can now use our custom vector literal syntax to initialize vectors with space-separated numbers:
std::vector<int> numbers = "1 2 3 4 5"_vec;
Conclusion
Custom vector literals provide a convenient way to initialize std::vector objects with a concise and intuitive syntax. By leveraging user-defined literals in C++, we can create our own custom suffixes and parsing logic to support vector literals. This allows for more readable and expressive code when working with vectors in C++.
Now that you have learned how to create custom vector literals, you can explore other variations and customization options based on your specific use cases.
#References