Home | History | Annotate | Line # | Download | only in m4 
      1 # Check for variable-length arrays.
      2 
      3 # serial 6
      4 
      5 # From Paul Eggert
      6 
      7 # Copyright (C) 2001, 2009-2022 Free Software Foundation, Inc.
      8 # This file is free software; the Free Software Foundation
      9 # gives unlimited permission to copy and/or distribute it,
     10 # with or without modifications, as long as this notice is preserved.
     11 
     12 m4_version_prereq([2.70], [], [
     13 
     14 # AC_C_VARARRAYS
     15 # --------------
     16 # Check whether the C compiler supports variable-length arrays.
     17 AC_DEFUN([AC_C_VARARRAYS],
     18 [
     19   AC_CACHE_CHECK([for variable-length arrays],
     20     ac_cv_c_vararrays,
     21     [AC_EGREP_CPP([defined],
     22        [#ifdef __STDC_NO_VLA__
     23         defined
     24         #endif
     25        ],
     26        [ac_cv_c_vararrays='no: __STDC_NO_VLA__ is defined'],
     27        [AC_COMPILE_IFELSE(
     28           [AC_LANG_PROGRAM(
     29              [[/* Test for VLA support.  This test is partly inspired
     30                   from examples in the C standard.  Use at least two VLA
     31                   functions to detect the GCC 3.4.3 bug described in:
     32                   https://lists.gnu.org/archive/html/bug-gnulib/2014-08/msg00014.html
     33                   */
     34                #ifdef __STDC_NO_VLA__
     35                 syntax error;
     36                #else
     37                  extern int n;
     38                  int B[100];
     39                  int fvla (int m, int C[m][m]);
     40 
     41                  int
     42                  simple (int count, int all[static count])
     43                  {
     44                    return all[count - 1];
     45                  }
     46 
     47                  int
     48                  fvla (int m, int C[m][m])
     49                  {
     50                    typedef int VLA[m][m];
     51                    VLA x;
     52                    int D[m];
     53                    static int (*q)[m] = &B;
     54                    int (*s)[n] = q;
     55                    return C && &x[0][0] == &D[0] && &D[0] == s[0];
     56                  }
     57                #endif
     58                ]])],
     59           [ac_cv_c_vararrays=yes],
     60           [ac_cv_c_vararrays=no])])])
     61   if test "$ac_cv_c_vararrays" = yes; then
     62     dnl This is for compatibility with Autoconf 2.61-2.69.
     63     AC_DEFINE([HAVE_C_VARARRAYS], 1,
     64       [Define to 1 if C supports variable-length arrays.])
     65   elif test "$ac_cv_c_vararrays" = no; then
     66     AC_DEFINE([__STDC_NO_VLA__], 1,
     67       [Define to 1 if C does not support variable-length arrays, and
     68        if the compiler does not already define this.])
     69   fi
     70 ])
     71 
     72 ])
     73