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| author | Paul Eggert <eggert@cs.ucla.edu> | 2019-05-24 14:59:11 -0700 |
|---|---|---|
| committer | Paul Eggert <eggert@cs.ucla.edu> | 2019-05-24 15:01:20 -0700 |
| commit | 0ffb8fd223dbc9ab6ec8aa33fb1cdf1056856344 (patch) | |
| tree | a77b573066a08ed96415ded3185a062ec5aa711a /m4 | |
| parent | 34d712407676b159bd72b79bedb3ddd788adb28d (diff) | |
| download | gnulib-0ffb8fd223dbc9ab6ec8aa33fb1cdf1056856344.tar.gz | |
flexmember: update comment
* m4/flexmember.m4 (AC_C_FLEXIBLE_ARRAY_MEMBER): Improve comment.
Diffstat (limited to 'm4')
| -rw-r--r-- | m4/flexmember.m4 | 10 |
1 files changed, 7 insertions, 3 deletions
diff --git a/m4/flexmember.m4 b/m4/flexmember.m4 index 1347068fe3..ef6373df29 100644 --- a/m4/flexmember.m4 +++ b/m4/flexmember.m4 @@ -34,10 +34,14 @@ AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER], AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [], [Define to nothing if C supports flexible array members, and to 1 if it does not. That way, with a declaration like 'struct s - { int n; double d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack + { int n; char d@<:@FLEXIBLE_ARRAY_MEMBER@:>@; };', the struct hack can be used with pre-C99 compilers. - When computing the size of such an object, don't use 'sizeof (struct s)' - as it overestimates the size. Use 'offsetof (struct s, d)' instead. + Use 'FLEXSIZEOF (struct s, d, N)' to calculate the size in bytes + of such a struct containing an N-element array, as both + 'sizeof (struct s) + N * sizeof (char)' and + 'offsetof (struct s, d) + N * sizeof (char)' + might compute a size that can cause malloc to align storage + improperly, even in C11. Don't use 'offsetof (struct s, d@<:@0@:>@)', as this doesn't work with MSVC and with C++ compilers.]) else |