why this statement will cause analysis error?

[Lu Fan <carboy.lu@xxxxxxxxx>]

Hi all:
I use a tool to check my code, and it reports a error on a statement:
like:

typedef a{
int m;
char sz_a[11];
char n;
}t_a;

typedef b{
int i;
char sz_b[11];
char j;
}t_b;

t_a* in;
t_b out;

//......

memcpy(in->sz_a, out.sz_b,sizeof(in->sz_a));

the memcpy will cause analysis error? The tool reports Overrun.

Thanks!