From: Alexei Sheplyakov <varg@metalica.kh.ua>
Date: Sat, 8 Aug 2009 10:02:47 +0000 (+0300)
Subject: G_eval: fix incorrect use of STL iterator.
X-Git-Tag: release_1-6-0~74
X-Git-Url: https://ginac.de/ginac.git/tutorial/ginac.git?a=commitdiff_plain;h=dda45abd8a2c408f8b3eb7959a10dfb2468ecc3a;p=ginac.git

G_eval: fix incorrect use of STL iterator.

According to [lib.bidirectional.iterators] it's not OK to decrement
an iterator pointing to the beginning of the sequence. Fortunately random
access iterators provided by (current versions of) gcc/libstdc++ don't have
this silly limitation, so the code which works with pointers works with
iterators without any changes at all. However,
 - there's no guarantee that the current behavior won't change in the future
 - some non-GNU compilers are not that smart (i.e. the program segfaults
   upon when decrementing beginning-of-the-sequence iterator).
---

diff --git a/ginac/inifcns_nstdsums.cpp b/ginac/inifcns_nstdsums.cpp
index 2c4061a9..b4105338 100644
--- a/ginac/inifcns_nstdsums.cpp
+++ b/ginac/inifcns_nstdsums.cpp
@@ -569,11 +569,12 @@ ex G_eval(const Gparameter& a, int scale, const exvector& gsyms)
 
 			Gparameter newa;
 			Gparameter::const_iterator it2 = short_a.begin();
-			for (--it2; it2 != it;) {
-				++it2;
+			for (; it2 != it; ++it2) {
 				newa.push_back(*it2);
 			}
+			newa.push_back(*it);
 			newa.push_back(a[0]);
+			it2 = it;
 			++it2;
 			for (; it2 != short_a.end(); ++it2) {
 				newa.push_back(*it2);