C pointer convertion cause memory access violation - c++

Question

I'm trying to migrate an old project from Borland BCC 5 to Qt 5.6.3 with Microsoft MSVC 2015 64bit compiler.
The following code is a model of original work. It works as expected in Visual Studio 2015 and Borland BCC 5, However, when I try to run it in Qt 5.6.3 with Qt Creator 3.6.1. It throws an error as "*hcID" is not accessible.
#include <stdlib.h>
typedef void (*ProcFoo) (void *pvData, unsigned long ulBarTag);
static char* gpcID = NULL;
typedef struct FooType
{
ProcFoo pfFoo; ///< pointer to Foo callback function
unsigned long ulBarTag; ///< base id
} FooType;
FooType* pFoo = NULL;
void RegisterAsFoo(unsigned long ulBarTag, ProcFoo pfFoo)
{
pFoo = (FooType*)malloc(sizeof(FooType));
pFoo->ulBarTag = ulBarTag;
pFoo->pfFoo = pfFoo;
}
void GetBarTag(unsigned long *pulBarTag, unsigned long ulBarTag)
{
*pulBarTag = ulBarTag;
}
int main()
{
char s[] = "Some Value";
gpcID = s;
char ** hcID = NULL;
RegisterAsFoo((unsigned long)&gpcID, (ProcFoo)GetBarTag);
pFoo->pfFoo(&hcID, pFoo->ulBarTag);
// after the execution, the hcID is still NULL in Qt 5.6.3, however,
// it is valid in Visual Studio 2015 and Borland BCC 5.
char* result = (*hcID);
return 1;
}
Thanks if you have any comments or ideas!

Answer 1

The problem is in the
(unsigned long)
cast which works for 32 bit.
Use
(unsigned long long)
instead. You need to do the replacement all over the place.
Otherwise, get rid of the int to pointer conversion or use a 32 bit compiler instead