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In this noncompliant code example, a user-defined literal n::x is operator"" x is declared. However, literal suffix identifiers are required to start with an underscore; literal suffixes without the underscore prefix are reserved for future library implementations:

#include <cstddef>
 
namespace n {
unsigned int operator"" x(const char *, std::size_t);
}

Compliant Solution (User-defined Literal)

In this compliant solution, the user-defined literal is named n::operator"" _x, which is not a reserved identifier:

#include <cstddef>

 
namespace n {
unsigned int operator"" _x(const char *, std::size_t);
}

Note that the name of the user-defined literal is operator"" _x and not _x, which would have otherwise been reserved to the global namespace.

Noncompliant Code Example (File Scope Objects)

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