[cfe-dev] sizeof (RopeRefCountString)

[Ted Kremenek]

On Sep 7, 2008, at 1:32 AM, Zhongxing Xu wrote:

> Hi,
>
> In RewriteRope.cpp, RewriteRope::MakeRopeString(const char *Start,  
> const char *End),
> we calculate the AllocSize by:
>
> unsigned AllocSize = sizeof(RopeRefCountString) - 1 + AllocChunkSize;
>
> I guess here the intention is: sizeof(RopeRefCountString) is 5. But  
> gcc says sizeof(RopeRefCountString) is 8. So the actual AllocSize is  
> 4087. Should we minus 4 instead of 1 to make the AllocSize 4084?

The "-1" I believe is to accommodate for the field Data[1], which  
occupies a single byte:

   struct RopeRefCountString {
     unsigned RefCount;
     char Data[1];  //  Variable sized.

     void addRef() { ... }
     void dropRef() { ... }
   };

By subtracting 1, the field "Data" refers to an array with size  
AllocChunkSize.