Return an array of structs.... What am I missng.

**shick** · 03-29-2014

cannot convert from 'Map *' to 'Map (*__w64 )[12][16]' I am thinking I overcomplicated this one or I just don't see it.

Code:

int map1[12][16]={
   {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1},
   {2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3},
   {3,3,3,4,3,3,3,3,3,3,3,3,3,3,2,3},
   {4,4,4,4,4,4,4,4,4,4,4,4,4,1,2,3},
   {3,3,3,3,3,3,3,3,3,3,3,3,4,1,2,3},
   {3,3,3,3,3,3,3,3,3,3,3,3,4,1,2,3},
   {1,3,3,3,3,3,3,3,3,3,3,3,4,1,2,3},
   {4,4,4,4,4,4,4,4,4,4,4,4,4,1,2,3},
   {1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,3},
   {2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,3},
   {3,3,3,3,3,3,3,3,3,3,3,3,3,3,2,3},
   {4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4}};


struct    Map
{
  public:
    int    Xpos; // X position in Pixels
    int    Ypos; // Y position in Pixels
    int    ID;   // The ID number that corresponds to the Bitmap to display
    };

 
Map* LoadMap(int lvl[12][16])
    {
      Map tm[12][16];
 
 
      for (int y=0; y<12; y++)
       {
        for (int x=0; x<16; x++)
          {
           tm[y][x].Xpos = x*50;
 
            if(lvl[y][x] == 1)
                 {
                   cout<<"1 ";
 
                  tm[y][x].ID = 1;
                 }
                if(lvl[y][x] == 2;
                   {
                      cout<<"2 ";
                      tm[y][x].ID = 2;
                   }
                 If(lvl[y][x] == 3)
                    {
                   cout<<"3 ";
                  tm[y][x].ID = 3;
                   }

                 if(lvl[y][x] == 4)
                  {
                  cout<<"4 ";
                  tm[y][x].ID = 4;
                  }
 
              }
 
                tm[y][x].Ypos= y*50;
 
cout<<"\n";
 
 
        }
return   *tm;                 // error is here or
 
    }



void main()
{

Map lvl1[12][16];               
 
&lvl1=LoadMap(map1);   // error is here

return;
}

**MutantJohn** · 03-29-2014

It looks like you're making a static allocation of data and then returning a pointer to it which I think will cause severe lifetime problems.

Also, the compiler is telling you that a pointer to a static allocation like what you're doing is not the same as a simple pointer to anywhere in the memory. So no more static, use dynamic.

**Elysia** · 03-29-2014

You cannot return a C array. Period. C arrays behave differently from all other data types.
Furthermore, returning a pointer to local stack data is undefined behaviour. The data will go away once the function ends which makes the pointer point to invalid data.

However, you can return an array if you use std::array or std::vector. The real C++ types that do not act special in any way.
Also, main shall return int and nothing else.

**rcgldr** · 03-29-2014

A function can return a pointer to a static or an allocated (malloc or new) array or matrix, but not a local array or matrix since it's memory on the stack effectively gets freed when the function returns. Syntax:

Code:

int (*returnptrtomatrix())[12][16]

**shick** · 03-31-2014

Thanks for the info guys. I have also figured out that my compiler (VS.net 2003) isn't doing me any favors as it is so out of date. I downloaded the new dev-C but if you know of a better one that's free I like to hear about it.

**Elysia** · 03-31-2014

You could just upgrade to Visual Studio 2013 Express. Dev-C++ has long since been abandoned (not maintained), to the best of my knowledge.

**Elkvis** · 03-31-2014

Originally Posted by Elysia

You could just upgrade to Visual Studio 2013 Express. Dev-C++ has long since been abandoned (not maintained), to the best of my knowledge.

Visual Studio is a great IDE, and in fact, it's the best one available for Windows, but its C++11 support is still pretty poor, even 2+ years and two major version releases after the standard's adoption. MinGW with G++ 4.8, and Code::Blocks, Eclipse or Netbeans would be good alternatives, if you want to make use of all that C++11 has to offer.

**Elysia** · 03-31-2014

Originally Posted by Elkvis

...but its C++11 support is still pretty poor, even 2+ years and two major version releases after the standard's adoption...

No, it's not. The latest version is pretty compliant.
Yes, it is missing a few bits here and there, but it's definitely not as poor as you make it out to be.
For reference, here is a list: C++11/14 Core Language Features in VS 2013 and the Nov 2013 CTP - Visual C++ Team Blog - Site Home - MSDN Blogs

Oh and btw, MinGW is not fully C++11/14 compliant, either.
If you want a compiler that support C++11 and complete Draft C++14, then Clang is a good choice.

**Elkvis** · 03-31-2014

Originally Posted by Elysia

No, it's not. The latest version is pretty compliant.
Yes, it is missing a few bits here and there, but it's definitely not as poor as you make it out to be.
For reference, here is a list: C++11/14 Core Language Features in VS 2013 and the Nov 2013 CTP - Visual C++ Team Blog - Site Home - MSDN Blogs

There is still a lot of "No" in that list, and many of them are things I use often. Obviously, individual preferences may vary, of course.

Originally Posted by Elysia

Oh and btw, MinGW is not fully C++11/14 compliant, either.
If you want a compiler that support C++11 and complete Draft C++14, then Clang is a good choice.

G++ 4.8 may not be 100 percent complete, but it's very close, and much closer, in fact, than VC++. 4.9 is going to be complete, but since it hasn't been released yet, it's not available with MinGW yet, nor (as far as I know) as a repository package for any Linux distro.

Good call on Clang. I haven't used it, but I've heard nothing but good things about it, except from people who have tried to build it from source on windows. I've been meaning to give it a try, but haven't found the time.

**Elysia** · 03-31-2014

Originally Posted by Elkvis

There is still a lot of "No" in that list, and many of them are things I use often. Obviously, individual preferences may vary, of course.

True, but that does not equal poor support. That's only the core features, too. It does not include the standard library, which to my knowledge, is fully compliant unless it depends on core features not yet supported in the compiler.
So while "many of them are things I use often" is a big negative to you, it may or may not be to others, and it does absolutely not imply that overall support is poor.

Good call on Clang. I haven't used it, but I've heard nothing but good things about it, except from people who have tried to build it from source on windows. I've been meaning to give it a try, but haven't found the time.

Clang has absolutely wonderful tools aside from being a wonderful compiler. The only problem is that it does not work with Visual Studio, which is kind of a dealbreaker for me.
As for building it on Windows... let's not go there. Been there once. Not going back.

**Elkvis** · 03-31-2014

Originally Posted by Elysia

As for building it on Windows... let's not go there. Been there once. Not going back.

That's exactly what I was referring to. I remember your thread on the tech board, and wouldn't wish your experiences on my worst enemies

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