Merge #28: Import fixes for sanitizer reported issues

1352543 Import fixes for sanitizer reported issues (fanquake)
d5fb869 refactor: use c++11 range based for loop in checkObject (fanquake)
ff9c379 refactor: Use nullptr (c++11) instead of NULL (Barry Deeney)
08a9975 build: use ax_cxx_compile_stdcxx.m4 to check for C++11 support (Barry Deeney)

Pull request description:

  See discussion in bitcoin/bitcoin#22646.

  Note that this code takes advantage of C++11 features, however this is fine, because this tree is for our downstream use, where we already require C++17.

  Co-authored-by: MarcoFalke <falke.marco@gmail.com>

ACKs for top commit:
  MarcoFalke:
    Concept ACK 1352543 🚍

Tree-SHA512: fbbee06630d3702953c290a5a4a2fe843770deb128534b62106230ecb020486b55dffdf25bf1acd6bc3f7f68c4539bc907e1fb159c3d2a95d4edaa00b1fcf8bd

Author: fanquake

build-aux/m4/ax_cxx_compile_stdcxx.m4

@@ -45,6 +45,9 @@ AC_SUBST(LIBUNIVALUE_AGE)
 LT_INIT
 LT_LANG([C++])
 
+dnl Require C++11 compiler (no GNU extensions)
+AX_CXX_COMPILE_STDCXX([11], [noext], [mandatory], [nodefault])
+
 case $host in
   *mingw*)
     LIBTOOL_APP_LDFLAGS="$LIBTOOL_APP_LDFLAGS -all-static"

configure.ac

@@ -45,7 +45,7 @@ static void outputEscape()
 
 	for (unsigned int i = 0; i < 256; i++) {
 		if (escapes[i].empty()) {
-			printf("\tNULL,\n");
+			printf("\tnullptr,\n");
 		} else {
 			printf("\t\"");
 

gen/gen.cpp

@@ -178,17 +178,19 @@ bool UniValue::findKey(const std::string& key, size_t& retIdx) const
 
 bool UniValue::checkObject(const std::map<std::string,UniValue::VType>& t) const
 {
-    if (typ != VOBJ)
+    if (typ != VOBJ) {
         return false;
+    }
 
-    for (std::map<std::string,UniValue::VType>::const_iterator it = t.begin();
-         it != t.end(); ++it) {
+    for (const auto& object: t) {
         size_t idx = 0;
-        if (!findKey(it->first, idx))
+        if (!findKey(object.first, idx)) {
             return false;
+        }
 
-        if (values.at(idx).getType() != it->second)
+        if (values.at(idx).getType() != object.second) {
             return false;
+        }
     }
 
     return true;
@@ -228,7 +230,7 @@ const char *uvTypeName(UniValue::VType t)
     }
 
     // not reached
-    return NULL;
+    return nullptr;
 }
 
 const UniValue& find_value(const UniValue& obj, const std::string& name)