Pointer value seems to be affected by value preceding it

[Senshi]

Hey everyone!

I normally don't cross-post, but I would really like to see this issue fixed and I feel like my StackOverflow question isn't really getting anywhere. Here's my problem:

In my current workflow I am exporting a 3D model along with various information (vertex colors, UV coordinates e.g.) from Blender through Python. This is stored in a binary file which can be read in C++.

Consider the following code:

Python:

ar = [0, 1, 2, 3, 4]
with open('model.bin', 'wb') as file:
    file.write(struct.pack('%si' & len(ar), *ar))

C++:

u32* ar = (u32*) model_bin; //model_bin is already declared externally
for(int i=0; i<5; i++){
    printf("%d\n", ar[i]);
}

This works! However, my file contains more than just one list of data. It contains a lot of data of different types. I keep track of this with the help of different pointers at the start of each new "element". I.e.:

rgb* vcols = (rgb*) model_bin;
u32* uvco = (u32*) ((char*) vcols + 2*numVcols)

Here is the full "stack": http://www.pasteall.org/51026/c

Right now, everything checks out, except for the first value of my UV textures. Setting it to 0 in my export script makes my C++ application read it as -566558720.

If I export and read the UV coordinate numbers as shorts however, everything works fine.

But it gets better! When I set the value of my last vcol[] element to 0, I can read the written int just fine! Setting the final vcol to 1 makes the first uvco read out as 65578.

I realize this is very tricky to debug without seeing the actual code and such, but perhaps someone can lend me some insights or suggestions based on this information?

Thanks,
Patrick

[Duthomhas]

I wonder if it is an alignment problem. Try to file.flush() after writing anything packed.

Wild guess here.

[Senshi]

Thanks for the suggestion, but no dice I'm afraid. =(

[JLBorges]

> In my current workflow I am exporting a 3D model along with various information
> (vertex colors, UV coordinates e.g.) from Blender through Python.
> This is stored in a binary file which can be read in C++.

How big is the size of this data set? Have you considered exporting the data as plain text?

[Senshi]

I'm using the data in a Nintendo DS library where I only have 4MB memory to work with. Doing it this way is nice and compact, and allows me to read straight from the specified pointers. =) So yes, I have considered it, but it's not very practical in this scenario.

EDIT: And it's fixed! There was an error with the data alignment. =) Thanks for the help!