C++11 introduced new forms of literals using modified syntax and semantics to provide User-Defined Literals (UDL) also known as Extensible Literals. While there was the ability to use them the standard library did not use any of them. In C++14, the commission added some standard literals. In this post, we explain user-defined literals operators and we explain some of these standard literals added in C++14.
What are the user defined literal operators in C++?
C++11 introduced new forms of literals using modified syntax and semantics in order to provide User-Defined Literals (UDL) also known as Extensible Literals. Using user-defined literals, user-defined classes can provide new literal syntax and they can be used with the operator "" to combine values with conversion operators. Here below, we explain how to use user-defined literals in C++.
What are the standard user-defined literals in C++14?
In C++14, we have some standard user-defined literal operators that comes with standard library. These are literals for basic strings, for chrono types, and for complex number types.
We can access to these operators by:
- using namespace std::literals;
- using namespace std::string_literals;
- using namespace std::literals::string_literals;
C++14 adds the following standard literals below,
For the string types there is an operator”” s() for basic string,
- s :
std::basic_stringtypes for creating the various string types std::string, std::wstring, etc.
here how we can use it with auto,
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auto str = "LearnCPlusPlus.org"s; // auto deduction to string |
Suffixes for std::chrono::duration values,
- h : hour type for the
std::chrono::durationtime intervals - m : minute type for the
std::chrono::durationtime intervals - s : second type for the
std::chrono::durationtime intervals - ms : millisecond type for the
std::chrono::durationtime intervals - ns : nanosecond type for the
std::chrono::durationtime intervals - us : u.second type for the
std::chrono::durationtime intervals
here how we can use them with auto,
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auto durh = 24h; // auto deduction to chrono::hours auto durm = 60min; // auto deduction to chrono::minutes auto durs = 120s; // auto deduction to chrono::seconds auto durms = 1000ms; // auto deduction to chrono::milliseconds auto durns = 2000ns; // auto deduction to chrono::nanoseconds |
Suffixes for complex number literals,
- if : imaginary number for the
std::complex<float>types - i : imaginary number for the
std::complex<double>types - il : imaginary number for the
std::complex<long double>types
here how we can use them with auto,
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auto zi = 5i; // auto deduction to complex<double> auto zif = 7if; // auto deduction to complex<float> auto zil = 9il; // auto deduction to complex<long double> |
there are more definitions.
Is there a full example of how to use standard user-defined literals in C++14?
Here is a full example about standard user-defined literals in C++.
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#include <iostream> #include <string> #include <iomanip> #include <complex> #include <chrono> using namespace std::literals; using namespace std::string_literals; // using namespace std::literals::string_literals; int main() { auto str = "LearnCPlusPlus.org"s; // auto deduction to string auto durh = 24h; // auto deduction to chrono::hours auto durm = 60min; // auto deduction to chrono::minutes auto durs = 120s; // auto deduction to chrono::seconds auto durms = 1000ms; // auto deduction to chrono::milliseconds auto durns = 2000ns; // auto deduction to chrono::nanoseconds auto zi = 5i; // auto deduction to complex<double> auto zif = 7if; // auto deduction to complex<float> auto zil = 9il; // auto deduction to complex<long double> } |
For more information about the standard user-defined literals, please see https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3402.pdf
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