std::vector inserting std::pair

Question

I am having trouble trying to insert a std::pair in the std::vector, with this code:

template <class R>
class AVectorContainner
{
public:
  AVectorContainner()
       {
         mVector= new std::vector<entry>;
       }
  typedef std::pair<int ,R *> entry;

  void insert(R* aPointer, int aID)
  {
     entry aEntry;
     aEntry=std::make_pair(aID,aPointer );
     mVector->push_back(aEntry);

  }
private: 
  std::vector<entry> * mVector;
}

This is the part of the main file, that I declare a pointer of a class and then I used it in the initialization of the template class.

In the main.cpp:

    int main()
    {
        SomeType * aTipe= new SomeType;
        int aID=1;
        AVectorContainer<SomeType> * aContainer= new AVectorContainer;
        aContainer->insert(aTipe,aId);//error line
delete aTipe;
delete aContainer;
        return 0;
    }

Compiler Output:

error: non-static reference member 'const int& std::pair<const int&, SomeType *>::first', can't use default assignment operator

error: value-initialization of reference type 'const int&'

... and not a copy-ctor or assignment operator to be seen. ugh. — WhozCraig, Aug 15 '13 at 18:50
Did you forget to add a semicolon ; after your class declaration or is that just a typo in this post? — AndyG, Aug 15 '13 at 18:51
@Yakk you shouldn't fix the OP's typos unless the OP fixes them himself. — Rapptz, Aug 15 '13 at 18:54
@Rapptz I assumed "error occurs on this line" was true. So I fixed typos prior to that line that would cause build breaks. — Yakk - Adam Nevraumont, Aug 15 '13 at 18:55
@Ricardo_arg -1 Show the real code, otherwise there'll be too much guessing going on. — jrok, Aug 15 '13 at 18:56
@Rapptz you shouldn't introduce typos into someone elses code either. — Yakk - Adam Nevraumont, Aug 15 '13 at 18:56
@Yakk Look at my revision, the extraneous brace was already there, I just put it in a code block. — Rapptz, Aug 15 '13 at 19:03
[The short version](http://ideone.com/Jw6c23) would seem a wee bit less prone to error, though I'm still not fond of that pointer. — WhozCraig, Aug 15 '13 at 19:09
Just my pet peeve but don't dynamically allocate a vector. There is rarely a reason to do so. — andre, Aug 15 '13 at 19:20
Congratulations! You have created a new programming language: **Java++** — Manu343726, Aug 15 '13 at 21:49
here is a similar post: stackoverflow.com/questions/634662/…, this one is facing the same problem. one of the comment to that question was this: blog.copton.net/archives/2007/10/13/stdvector/index.html. The code doesnt compile, so fixit filling with semicolons and other isses doesnt seemt to improve the quality of the question, the compiler again is ringing with the same output, sorry but those anwser doesnt respond the question. — Ricardo_arg, Aug 15 '13 at 21:57
http://sscce.org -- if you cannot provide a simple, self contained, compiling-until-the-error example, the only way we can figure out your problem is by reading your mind. This is not a mind reading website. Provide code that *actually demonstrates the error*. — Yakk - Adam Nevraumont, Aug 15 '13 at 22:32
@Ricardo_arg the code you edited into my answer below, and the code you have above, are fundamentally different. — Yakk - Adam Nevraumont, Aug 16 '13 at 19:19

score 2 · Answer 1 · answered Aug 15 '13 at 19:04

Fixed all typos, compare the two ... he did like 100 in 20 lines!

#include <vector>
#include <utility>

template <class R>
class AVectorContainer
{
public:
  AVectorContainer()
       {
         mVector= new std::vector<entry>;
       }
  typedef std::pair<int ,R *> entry;

  void insert(R* aPointer, int aID)
  {
     entry aEntry;
     aEntry=std::make_pair(aID,aPointer );
     mVector->push_back(aEntry);

  }
private: 
  std::vector<entry> * mVector;
};

class SomeType
{
public:
    SomeType(){ x=5; }
    ~SomeType(){ }
    int x;
};

int main()
{
    SomeType * aTipe= new SomeType;
    int aID=1;
    AVectorContainer<SomeType> * aContainer= new AVectorContainer<SomeType>;
    aContainer->insert(aTipe,aID);//error line
    return 0;
}

Yakk - Adam Nevraumont · Accepted Answer · 2013-08-16T19:19:05.850

The original poster failed to actually post the code that was causing the problem.

He has since edited my post with the correct code that demonstrates the problem. The code that demonstrates the problem follows:

template <class R, typename B=int>
class AVectorContainer
{
public:
  AVectorContainer() {}
  typedef R* ptr_Type;
  typedef const B & const_ref_Type;
  typedef std::pair<const_ref_Type ,ptr_Type> entry;


  void insert(ptr_Type aPointer, const_ref_Type aID) {
     entry aEntry=std::make_pair(aID,aPointer);
     mVector.push_back(aEntry);
  }
private:
  std::vector<entry> mVector;
};

class SomeType
{
public:
  SomeType(){ x=5; }
  ~SomeType(){ }
  int x;
};

int main()
{
  SomeType * aTipe= new SomeType;
  int aID=1;
  AVectorContainer<SomeType> aContainer;
  aContainer.insert(aTipe,aID);
  return 0;
}

Compiler output:

/usr/include/c++/4.7/bits/stl_pair.h:88: error: non-static reference member 'const int& std::pair<const int&, SomeType*>::first', can't use default assignment operator

The flaw is in these lines:

  typedef R* ptr_Type;
  typedef const B & const_ref_Type;
  typedef std::pair<const_ref_Type ,ptr_Type> entry;
  std::vector<entry> mVector;

Here, the original poster attempts to make a vector of pairs that contain a constant reference, and then does this:

entry aEntry;
aEntry=std::make_pair(aID,aPointer )

this attempts to assign one pair to another. But const& variables cannot be assigned to another -- they can be constructed (initialized) from another const&, but not assigned.

An easy fix is:

entry aEntry=std::make_pair(aID,aPointer )

so that we are not constructing aEntry from another entry, instead of default constructing aEntry (which is also illegal: const& must be initialized), then assigning to it.

True, I didn't pay much attention to the actual code. I was too busy `SnD'ing` the typos! — gifnoc-gkp, Aug 15 '13 at 19:25
seriously?? this is a solution?? just checking the types and adding some class that was just writting for showing proposing?. — Ricardo_arg, Aug 15 '13 at 21:03
@Ricardo_arg it wasn't much of a question. Your code was full of typos -- TheOtherGuy fixed that. I noticed you also had a pile of unnecessary `new`s: rather than editing TheOtherGuy's answer to remove them, I tossed it out here. If ThatOtherGuy improved his answer, I'd just delete mine. — Yakk - Adam Nevraumont, Aug 15 '13 at 21:32
here is a similar post: http://stackoverflow.com/questions/634662/non-static-const-member-cant-use-default-assignment-operator, this one is facing the same problem. one of the comment to that question was this: http://blog.copton.net/archives/2007/10/13/stdvector/index.html. The code doesnt compile, so fixit filling with semicolons and other isses doesnt seemt to improve the quality of the question, the compiler again is ringing with the same output, sorry but those anwser doesnt respond the question. — Ricardo_arg, Aug 15 '13 at 21:50
The code I wrote compiles. I even link to a live example. If yours does not, maybe your compiler us broken, or maybe your code is different than mine. @ricardo_arg — Yakk - Adam Nevraumont, Aug 15 '13 at 22:28

score 0 · Answer 3 · answered Aug 15 '13 at 19:01

0

After fixing all the typo's (Containner, aId, missing ; etc.) the code compiles just fine.

answered Aug 15 '13 at 19:01

nullptr

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std::vector inserting std::pair

3 Answers3