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 12m4_version_prereq([2.70], [], [ 13 14# AC_C_VARARRAYS 15# -------------- 16# Check whether the C compiler supports variable-length arrays. 17AC_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