Re: boost ptr_map memory access violation

From: roland kapl (roland.kapl_at_[hidden])
Date: 2021-01-08 21:28:40

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::vector<std::vector<std::string>> &control,
                   const std::vector<std::vector<std::vector<std::string>>> &data,
                   pt::ptree & ptTree)
{
    // now the map is local...
   typedef std::map<std::string, pt::ptree*> treeMap;
    std::map<std::string, treeMap> 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<std::string, pt::ptree> && 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<std::string, pt::ptree*> && 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/treeizereld.cpp

-regards,
Roland

----------------------------------------------------------------------

Message: 1

Date: Wed, 6 Jan 2021 11:49:07 +0000

From: roland kapl <roland.kapl_at_[hidden]<mailto:roland.kapl_at_[hidden]>>

To: "boost-users_at_[hidden]<mailto:boost-users_at_[hidden]>" <boost-users_at_[hidden]<mailto:boost-users_at_[hidden]>>

Subject: [Boost-users] boost ptr_map memory access violation

                (stack/heap problem)

Message-ID:

                <AM0PR03MB424285F7832EDC3C73C96860EDD00_at_AM0PR03MB4242.eurprd03.prod.outlook.c<mailto:AM0PR03MB424285F7832EDC3C73C96860EDD00_at_AM0PR03MB4242.eurprd03.prod.outlook.c>>

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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<std::string, pt::ptree> treeMap; std::map<std::string, treeMap> 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::vector<std::vector<std::string>>& control,

    const std::vector<std::vector<std::vector<std::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::vector<std::vector<std::string>> &control,

                   const std::vector<std::vector<std::vector<std::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

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