liveBook · Manning

Incompatible types

As explained in Modern C

Incompatible types are C types that are not permitted to denote the same compatible type for a particular language construct.

A _Generic expression selects one expression by the type of its controlling expression. Its listed type expressions must be mutually incompatible, so the compiler can choose exactly one match. TAKEAWAY: incompatible types are C types that cannot denote the same compatible type for this construct. section 16.6

Selecting a type-specific function

The fabs macro associates float with fabsf and long double with fabsl, leaving fabs as the default. These associations illustrate distinct type cases in a type-generic interface.

Keep these related constraints in view:

  • Require an unambiguous compile-time choice among the type expressions. section 16.6
  • Reject a pointer to a variable-length array as a _Generic type expression. section 16.6
  • Keep every choice expression valid, including alternatives that are not selected. section 16.6

How Modern C covers it

How deep it goes
Defines mutual incompatibility, forbids pointer-to-VLA associations, and emphasizes validity of every choice expression.
Examples
Demonstrates fabs dispatch and an invalid TRACE_CONVERT alternative involving integer-to-pointer assignment.
What you can do after
Diagnose _Generic macros by checking type compatibility, ambiguity, forbidden pointer-to-VLA associations, and all alternative expressions.
How it connects
Connects _Generic expressions, type-generic programming, compatible types, and pointers to variable-length arrays.
Cover of Modern C
liveBookmanning.com
Read Modern C on liveBook Get the book at manning.com

This explainer was generated by Manning's knowledge graph from the text of Modern C. The section links point to the parts of the book it draws on.