--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,12 @@
+2010-04-05  Bruno Haible  <bruno@clisp.org>
+
+	memchr: Avoid a possible C++ test error.
+	* lib/string.in.h (memchr): Provide declaration if function is missing.
+	* m4/memchr.m4 (gl_FUNC_MEMCHR): If the function is missing, set
+	HAVE_MEMCHR to 0, not REPLACE_MEMCHR to 1.
+	* m4/string_h.m4 (gl_HEADER_STRING_H_DEFAULTS): Initialize HAVE_MEMCHR.
+	* modules/string (Makefile.am): Substitute HAVE_MEMCHR.
+
 2010-04-05  Bruno Haible  <bruno@clisp.org>
 
 	strtok_r: Improve idiom.

--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -66,6 +66,11 @@
                                   _GL_ARG_NONNULL ((1)));
 _GL_CXXALIAS_RPL (memchr, void *, (void const *__s, int __c, size_t __n));
 # else
+#  if ! @HAVE_MEMCHR@
+_GL_FUNCDECL_SYS (memchr, void *, (void const *__s, int __c, size_t __n)
+                                  __attribute__ ((__pure__))
+                                  _GL_ARG_NONNULL ((1)));
+#  endif
   /* On some systems, this function is defined as an overloaded function:
        extern "C" { const void * std::memchr (const void *, int, size_t); }
        extern "C++" { void * std::memchr (void *, int, size_t); }  */

--- a/m4/memchr.m4
+++ b/m4/memchr.m4
@@ -1,4 +1,4 @@
-# memchr.m4 serial 7
+# memchr.m4 serial 8
 dnl Copyright (C) 2002-2004, 2009-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -13,12 +13,7 @@
 
   dnl These days, we assume memchr is present.  But just in case...
   AC_REQUIRE([gl_HEADER_STRING_H_DEFAULTS])
-  AC_REPLACE_FUNCS([memchr])
-  if test $ac_cv_func_memchr = no; then
-    gl_PREREQ_MEMCHR
-    REPLACE_MEMCHR=1
-  fi
-
+  AC_CHECK_FUNCS_ONCE([memchr])
   if test $ac_cv_func_memchr = yes; then
     # Detect platform-specific bugs in some versions of glibc:
     # memchr should not dereference anything with length 0
@@ -73,10 +68,14 @@
       [dnl Be pessimistic for now.
        gl_cv_func_memchr_works="guessing no"])])
     if test "$gl_cv_func_memchr_works" != yes; then
-      gl_PREREQ_MEMCHR
       REPLACE_MEMCHR=1
-      AC_LIBOBJ([memchr])
     fi
+  else
+    HAVE_MEMCHR=0
+  fi
+  if test $HAVE_MEMCHR = 0 || test $REPLACE_MEMCHR = 1; then
+    AC_LIBOBJ([memchr])
+    gl_PREREQ_MEMCHR
   fi
 ])
 

--- a/m4/string_h.m4
+++ b/m4/string_h.m4
@@ -76,6 +76,7 @@
   GNULIB_STRVERSCMP=0;  AC_SUBST([GNULIB_STRVERSCMP])
   HAVE_MBSLEN=0;        AC_SUBST([HAVE_MBSLEN])
   dnl Assume proper GNU behavior unless another module says otherwise.
+  HAVE_MEMCHR=1;                AC_SUBST([HAVE_MEMCHR])
   HAVE_DECL_MEMMEM=1;           AC_SUBST([HAVE_DECL_MEMMEM])
   HAVE_MEMPCPY=1;               AC_SUBST([HAVE_MEMPCPY])
   HAVE_DECL_MEMRCHR=1;          AC_SUBST([HAVE_DECL_MEMRCHR])

--- a/modules/string
+++ b/modules/string
@@ -62,6 +62,7 @@
 	      -e 's|@''GNULIB_STRVERSCMP''@|$(GNULIB_STRVERSCMP)|g' \
 	      < $(srcdir)/string.in.h | \
 	  sed -e 's|@''HAVE_MBSLEN''@|$(HAVE_MBSLEN)|g' \
+	      -e 's|@''HAVE_MEMCHR''@|$(HAVE_MEMCHR)|g' \
 	      -e 's|@''HAVE_DECL_MEMMEM''@|$(HAVE_DECL_MEMMEM)|g' \
 	      -e 's|@''HAVE_MEMPCPY''@|$(HAVE_MEMPCPY)|g' \
 	      -e 's|@''HAVE_DECL_MEMRCHR''@|$(HAVE_DECL_MEMRCHR)|g' \