mongoCXX: SIG: SEGFAULT while calling find_one()

[javantamt]

Hey there!

I'm trying to implement some easy wrapper for mongoDB in withe the new cxx driver.
Calling in this assambly the funcion find_one() is throwing a segfault. I don't know why.
It looks like an obvious misstake...

Member function:

int CMongo::FindOne(std::string strJSONFind, std::string strJSONOrderBy, core::v1::optional<bsoncxx::v_noabi::document::value> &docReturn ){

  int iErr = 0;

  mongocxx::options::find MyFindOptions{};
  MyFindOptions.sort(bsoncxx::from_json(strJSONOrderBy).view());
  // core::v1::optional<bsoncxx::v_noabi::document::value> XXX;

  try{
  //docReturn = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions);    // SEGFAULT
  // XXX = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions); // segfault
   // auto i = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions); // segfault
    auto i = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions);  // segfault

Class header:

class CMongo {
public:
  CMongo();

  int FindOne(
      std::string strJSONFind,
      std::string strJSONOrderBy,
      core::v1::optional<bsoncxx::v_noabi::document::value> &docReturn );
  virtual ~CMongo();

private:
  mongocxx::client conn;    // connection to database
  class mongocxx::v_noabi::collection collJobs;    
};

Class Constructor:

CMongo::CMongo() {
  // TODO Put this in every init functions withe a question of existence
  mongocxx::client conn(mongocxx::uri("Mongo credentiales" ));
  collJobs = conn["Database"]["collection"];
}

Function Call:

  CMongo MyMongo;
  core::v1::optional<bsoncxx::v_noabi::document::value> ReturnVal;
  MyMongo.FindOne("{\"started\":false}","{\"date\":1,\"priority\":1}",ReturnVal);

[Andrew Morrow]

On Mon, May 2, 2016 at 5:54 PM, javantamt <java...@gmail.com> wrote:

Hey there!

 

Calling in this assambly the funcion find_one() is throwing a segfault. I don't know why.
It looks like an obvious misstake...

I think I know what the problem is, see below.

 

Member function:

int CMongo::FindOne(std::string strJSONFind, std::string strJSONOrderBy, core::v1::optional<bsoncxx::v_noabi::document::value> &docReturn ){

  int iErr = 0;

  mongocxx::options::find MyFindOptions{};
  MyFindOptions.sort(bsoncxx::from_json(strJSONOrderBy).view());
  // core::v1::optional<bsoncxx::v_noabi::document::value> XXX;

  try{
  //docReturn = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions);    // SEGFAULT
  // XXX = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions); // segfault
   // auto i = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions); // segfault
    auto i = collJobs.find_one(bsoncxx::from_json(strJSONFind).view(),MyFindOptions);  // segfault

Note: this isn't your problem, but you shouldn't need the .view calls above. The bsoncxx::from_json is an rvalue and should be able to be passed directly to find_one.

 

Class header:

class CMongo {
public:
  CMongo();

  int FindOne(
      std::string strJSONFind,
      std::string strJSONOrderBy,
      core::v1::optional<bsoncxx::v_noabi::document::value> &docReturn );
  virtual ~CMongo();

private:
  mongocxx::client conn;    // connection to database
  class mongocxx::v_noabi::collection collJobs;    
};

Class Constructor:

CMongo::CMongo() {
  // TODO Put this in every init functions withe a question of existence
  mongocxx::client conn(mongocxx::uri("Mongo credentiales" ));
  collJobs = conn["Database"]["collection"];
}

I think you haven't actually initialized the member CMongo::conn here - you have shadowed it, and created a temporary mongocxx::client object called 'conn' on the stack. You then use that to initialize CMongo::collJobs, and it immediately goes out of scope.

That is not a legal usage: the collection object must outlive the connection object that produced it.

Can you see if your segfault is resolved if you write this as:

conn = mongocxx:client(mongocxx::uri("Mongo credentiales" ));

Even better would be to initialize conn in the member initializer list in CMongo::CMongo.

I recommend running your application under valgrind or AddressSanitizer to find these sorts of mistakes.

[javantamt]

Note: this isn't your problem, but you shouldn't need the .view calls above.

It was my problem. Thx for this =).