gnulib/doc/noreturn.texi

@c GNU noreturn, stdnoreturn modules documentation

@c Copyright (C) 2019--2020 Free Software Foundation, Inc.

@c Permission is granted to copy, distribute and/or modify this document
@c under the terms of the GNU Free Documentation License, Version 1.3 or
@c any later version published by the Free Software Foundation; with no
@c Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A
@c copy of the license is at <https://www.gnu.org/licenses/fdl-1.3.en.html>.

@node Non-returning Functions
@section Non-returning Functions

@cindex @code{_Noreturn}
@cindex @code{noreturn}
@cindex @code{stdnoreturn}
A "non-returning" function is a function which cannot return normally.
It can transfer control only through @code{longjmp()}, @code{throw}
(in C++), or similar mechanisms.  The most prominent function of this
class is the @code{abort} function.  Non-returning functions are
declared with a @code{void} return type.

It helps the compiler's ability to emit sensible warnings, following
data-flow analysis, to declare which functions are non-returning.

Gnulib has two modules that support such a declaration:

@itemize @bullet
@item
The @samp{stdnoreturn} module.  It provides a way to put this
declaration at function declarations and function definitions, but not
in function pointer types.  The identifier to use is @code{_Noreturn}
or @code{noreturn}; @code{_Noreturn} is to be preferred because
@code{noreturn} is a no-op on some platforms.  The include file is
@code{<stdnoreturn.h>}.

@item
The @samp{noreturn} module.  It provides a way to put this declaration
at function declarations, at function definitions, and in function
pointer types.  The identifiers to use are:
@itemize -
@item
@code{_GL_NORETURN_FUNC} for use in function declarations and function
definitions.
@item
@code{_GL_NORETURN_FUNCPTR} for use on function pointers.
@end itemize
@noindent
The include file is @code{<noreturn.h>}.
@end itemize

Which of the two modules to use?  If the non-returning functions you
have to declare are unlikely to be accessed through function pointers,
you should use module @code{stdnoreturn}; otherwise the module
@code{noreturn} provides for better data-flow analysis and thus for
better warnings.

For a detailed description of the @code{stdnoreturn} module, see
@ref{stdnoreturn.h}.