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Diffstat (limited to 'm4/flexmember.m4')
| -rw-r--r-- | m4/flexmember.m4 | 46 |
1 files changed, 46 insertions, 0 deletions
diff --git a/m4/flexmember.m4 b/m4/flexmember.m4 new file mode 100644 index 0000000..db93cf3 --- /dev/null +++ b/m4/flexmember.m4 @@ -0,0 +1,46 @@ +# serial 5 +# Check for flexible array member support. + +# Copyright (C) 2006, 2009-2018 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 +]) |