Why Do Libraries Use Hexadecimal Constants Instead of Enums?

Hexadecimal is only a way of writing the integer; the value itself is still just a number. It is useful when the bit pattern matters because each hex digit corresponds to exactly four binary bits. In this example, the shared 0x0001 prefix may identify an error category or leave room for related groups of values, which is much easier to see in hex than in decimal.

Sometimes the numbers are part of an external convention or specification, so changing them could break compatibility. Even when there is no strict external requirement, stable numeric codes are useful when values cross library boundaries, get logged, or are handled by bindings written in other languages. The hexadecimal spelling simply makes those stable values and their structure easier to inspect.

A C enum could technically contain these exact values, but enums in C have limited type-safety and less control over their underlying representation. Named macros or typed integer constants are also easy to expose consistently to other languages and APIs, which matters for a cross-platform library.