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-rw-r--r--m4/flexmember.m446
1 files changed, 46 insertions, 0 deletions
diff --git a/m4/flexmember.m4 b/m4/flexmember.m4
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+# serial 5
+# Check for flexible array member support.
+
+# Copyright (C) 2006, 2009-2019 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# Written by Paul Eggert.
+
+AC_DEFUN([AC_C_FLEXIBLE_ARRAY_MEMBER],
+[
+ AC_CACHE_CHECK([for flexible array member],
+ ac_cv_c_flexmember,
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdlib.h>
+ #include <stdio.h>
+ #include <stddef.h>
+ struct m { struct m *next, **list; char name[]; };
+ struct s { struct s *p; struct m *m; int n; double d[]; };]],
+ [[int m = getchar ();
+ size_t nbytes = offsetof (struct s, d) + m * sizeof (double);
+ nbytes += sizeof (struct s) - 1;
+ nbytes -= nbytes % sizeof (struct s);
+ struct s *p = malloc (nbytes);
+ p->p = p;
+ p->m = NULL;
+ p->d[0] = 0.0;
+ return p->d != (double *) NULL;]])],
+ [ac_cv_c_flexmember=yes],
+ [ac_cv_c_flexmember=no])])
+ if test $ac_cv_c_flexmember = yes; then
+ 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
+ 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.
+ Don't use 'offsetof (struct s, d@<:@0@:>@)', as this doesn't work with
+ MSVC and with C++ compilers.])
+ else
+ AC_DEFINE([FLEXIBLE_ARRAY_MEMBER], [1])
+ fi
+])