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assert.3: Document static_assert and _Static_assert

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Reviewed by:	imp, 0mp
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D29833
This commit is contained in:
Faraz Vahedi 2021-04-20 10:50:36 +02:00 committed by Mateusz Piotrowski
parent 6bc0bb2936
commit 33f8d79d76
2 changed files with 36 additions and 2 deletions
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1
share/man/man3/Makefile
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@ -72,6 +72,7 @@ MLINKS= arb.3 ARB8_ENTRY.3 \
arb.3 ARB_RIGHT.3 \
arb.3 ARB_RIGHTIDX.3 \
arb.3 ARB_ROOT.3
MLINKS+= assert.3 static_assert.3
MLINKS+= ATOMIC_VAR_INIT.3 atomic_compare_exchange_strong.3 \
ATOMIC_VAR_INIT.3 atomic_compare_exchange_strong_explicit.3 \
ATOMIC_VAR_INIT.3 atomic_compare_exchange_weak.3 \

37
share/man/man3/assert.3
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@ -28,15 +28,18 @@
.\" @(#)assert.3 8.1 (Berkeley) 6/9/93
.\" $FreeBSD$
.\"
.Dd May 31, 2018
.Dd April 20, 2021
.Dt ASSERT 3
.Os
.Sh NAME
.Nm assert
.Nm assert ,
.Nm static_assert
.Nd expression verification macro
.Sh SYNOPSIS
.In assert.h
.Fn assert expression
.Fn static_assert expression
.Fn static_assert expression message
.Sh DESCRIPTION
The
.Fn assert
@ -81,6 +84,21 @@ The
macro should only be used for ensuring the developer's expectations
hold true.
It is not appropriate for regular run-time error detection.
.Pp
The
.Fn static_assert
macro expands to
.Fn _Static_assert ,
and, contrarily to
.Fn assert ,
makes assertions at compile-time.
Once the constraint is violated, the compiler produces a diagnostic
message including the string literal message, if provided.
The initial form of the
.Fn _Static_assert
containing a string literal message was introduced in C11 standard, and
the other form with no string literal is to be implemented by C2x and
some compilers may lack its adoption at present.
.Sh EXAMPLES
The assertion:
.Dl "assert(1 == 0);"
@ -95,14 +113,29 @@ indicate a bug.
Second, the code will disappear if
.Dv NDEBUG
is defined, changing the semantics of the program.
.Pp
The following asserts that the size of the S structure is 16.
Otherwise, it produces a diagnostic message which points at the
constraint and includes the provided string literal:
.Dl "static_assert(sizeof(struct S) == 16, ""size mismatch"");"
If none is provided, it only points at the constraint.
.Sh SEE ALSO
.Xr abort2 2 ,
.Xr abort 3
.Sh STANDARDS
.Rs
The
.Fn assert
macro conforms to
.St -isoC-99 .
.Re
.Pp
.Rs
The
.Fn static_assert
macro conforms to
.St -isoC-2011 .
.Re
.Sh HISTORY
An
.Nm