why only char* is a <Bad Ptr>, and not other data types?

Question

I am learning about pointers in C++. When initializing pointers, for example,

double* pvalue1 = nullptr;//okay
char* pvalue2 = nullptr;  //only this says, "0x00000000 <Bad Ptr>" (in the watch window of Visual C++ 2010)
int* pvalue3 = nullptr;   //okay

Why does only the char type pointer give Bad Ptr while other pointer types don't?

I don't care about the pointed-to values at the moment. I am not dereferencing them (that's why there are those errors above). I am just looking at the watch window for those three pointers.

Answer 1

For most pointer types, the Watch window in Visual Studio displays the value of the pointer (the address to which it points), and allows you to access the pointed-to value by expanding the + icon. So for a null pointer to, let's say, int, it will simply show null or 0x00000000 or something like that.

char*s are handled differently. Here, the Watch does not show the pointer value at all, but directly interprets the pointed-to data as a NUL-terminated string and prints that. This of course means that a null char* does not give meaningful results, hence the Bad Ptr.

In other words, Watch itself automatically does the dereferencing for char* pointers (and only for those).

Answer 2

Presumably, whatever you're using to display the pointer values will also display whatever string a char* pointer points to, since such pointers are sometimes used to point to strings.

In this case, being null, it doesn't point to any string, so whatever is displaying it tells you that instead.