I was testing a C++ project of mine with older versions of GCC, and
mistakingly used the following command:
$ ./configure CXX=gcc-4.7
Autoconf didn't spot any problem:
> checking whether the C++ compiler works... yes
But of course gcc-4.7 doesn't know how to link a C++ program, so my
build failed.
The attached patch fixes this problem by changing the C++ null program
into:
int main() { (void) new int; return 0; }
Any C++ compiler, even an ancient one, should be able to pass that test,
but C compilers will fail. In GCC's case, the program will compile but
the link will fail because libc doesn't contain an 'operator new'.
Index: autoconf-2.69/lib/autoconf/c.m4
===================================================================
--- autoconf-2.69.orig/lib/autoconf/c.m4 2012-01-21 14:46:39.000000000 +0100
+++ autoconf-2.69/lib/autoconf/c.m4 2014-02-05 10:06:25.172408390 +0100
@@ -247,6 +247,14 @@
])
+# _AC_LANG_NULL_PROGRAM(C++)
+# --------------------------
+# To distinguish a C++ compiler from a C compiler, test if we can compile
+# and link a program with a C++-specific construct.
+m4_define([_AC_LANG_NULL_PROGRAM(C++)],
+[AC_LANG_PROGRAM([], [(void) new int;])])
+
+
# AC_LANG_CPLUSPLUS
# -----------------
AU_DEFUN([AC_LANG_CPLUSPLUS], [AC_LANG(C++)])
