Dear All!
After finding some inspiration on https://stackoverflow.com/questions/4088387/how-to-store-pointers-in-map , I've succeeded storing the property tree pointers in a std::map...
std::string TreeizeRelD::writeTree(const std::vectorstd::string> &control,
const std::vectorstd::string>> &data,
pt::ptree & ptTree)
{
// now the map is local...
typedef std::map treeMap;
std::map parentTableTrees;
....
std::string subRootNode = parentNode + (subnodeOfParent != "" ? "." + subnodeOfParent : "");
std::string tableLookup = subRootNode + "." + rootElemRec;
// simply add records if no foreign key name exists (usually the top (root) table)
if (foreignKeyName == "") {
for (std::pair && keyPair : tables[tableLookup]) {
parentTableTrees[subRootNode].insert(std::make_pair(keyPair.first, &ptTree.add_child(subRootNode, keyPair.second)));
...
// iterate through all parent key record collections referred to by subtables parentNode (rootnode + optional subnode)
for (std::pair && parentKeysPair : parentTableTrees.find(lookupNode)->second) {
// iterate through all records (ptrees) in key collection
for (pt::ptree::iterator parentRecPair = parentKeysPair.second->begin(); parentRecPair != parentKeysPair.second->end(); ++parentRecPair) {
// important here: assign a reference to parentRecPtree (pointer!), otherwise a copy is created!
pt::ptree &parentRecPtree = parentRecPair->second;
...
parentTableTrees[subRootNode].insert(std::make_pair(rowsFK, &parentRecPair->second.get_child(subnodeFRec)));
...
parentTableTrees[subRootNode].insert(std::make_pair(rowsFK, &parentRecPtree.put_child(subnodeOfParent, foreignRecordset)));
The complete source of this: https://github.com/rkapl123/OreControl/blob/master/OreMgr/TreeizeRelD/treeiz...
-regards,
Roland
----------------------------------------------------------------------
Message: 1
Date: Wed, 6 Jan 2021 11:49:07 +0000
From: roland kapl mailto:roland.kapl@hotmail.com>
To: "boost-users@lists.boost.orgmailto:boost-users@lists.boost.org" mailto:boost-users@lists.boost.org>
Subject: [Boost-users] boost ptr_map memory access violation
(stack/heap problem)
Message-ID:
mailto:AM0PR03MB424285F7832EDC3C73C96860EDD00@AM0PR03MB4242.eurprd03.prod.ou...>
Content-Type: text/plain; charset="us-ascii"
Dear Boost-Experts!
I'm trying to use a ptr_map along with boost property trees. I need to store pointers to specific parts of a built up property tree to access these parts later on for easy insertion there.
However, when the ptr_map is cleared/destroyed, I get memory access violations/stack overflow messages for my test cases.
The ptr_map (typedef treeMap) is globally defined within a std::map to a ptr_map to property trees as follows (I know this isn't good practice, but passing it as a reference didn't make a difference, so I left it that way):
namespace pt = boost::property_tree;
typedef boost::ptr_map treeMap; std::map parentTableTrees;
The property tree is defined as follows in this function (this builds a property tree from tabular data in the passed table variable "data" using definitions form table variable "control"):
std::string TreeizeRelD::writeTreeAndCreateXML(const std::vectorstd::string>& control,
const std::vectorstd::string>>& data, int *result) {
std::string resultString;
pt::ptree &propTree = pt::ptree();
std::string returnStr = TreeizeRelD::writeTree(control, data, propTree);
*result = 0;
if (returnStr != "") {
*result = 1;
return returnStr;
}
returnStr = TreeizeRelD::createXML(propTree, resultString);
if (returnStr != "") {
*result = 1;
return returnStr;
}
// here the memory access violation occurs:
parentTableTrees.clear();
return resultString;
}
In function writeTree the propTree (being passed by ref as ptTree) is populated in following three lines:
std::string TreeizeRelD::writeTree(const std::vectorstd::string> &control,
const std::vectorstd::string>> &data,
pt::ptree & ptTree)
...
// FIRST LINE
parentTableTrees[subRootNode].insert(keyPair.first, &ptTree.add_child(subRootNode, keyPair.second)); ...
// iterate through all parent key record collections referred to by subtables parentNode (rootnode + optional subnode)
for (treeMap::value_type && parentKeysPair : parentTableTrees.find(lookupNode)->second) {
// iterate through all records (ptrees) in key collection
for (pt::ptree::iterator parentRecPair = parentKeysPair.second->begin(); parentRecPair != parentKeysPair.second->end(); ++parentRecPair) {
pt::ptree &parentRecPtree = parentRecPair->second; ...
// SECOND LINE
// parentRecPair is an iterator variable from the ptr_map:
parentTableTrees[subRootNode].insert(rowsFK, &parentRecPair->second.get_child(subnodeFRec));
...
// THIRD LINE
// parentRecPtree is the referenced property tree itself:
parentTableTrees[subRootNode].insert(rowsFK, &parentRecPtree.put_child(subnodeOfParent, foreignRecordset));
I already have the suspicion that the memory access violation comes from ptr_map taking ownership of the pointers (references) passed to it in the above three lines and that these are all created on the stack and not the heap, where ptr_map expects them to be.
When the ptr_map is finally destroyed, it tries to access memory, that's impossible to access...
But I didn't manage to successfully create heap objects that also do NOT copy the property tree objects, which is important as I only need references to the property trees.
Any help is appreciated.
-regards,
Roland
