Currency data type of VB 6 to C++

Question

hi, I am calling a C++ function from VB6. In which I need to pass variable of Currency datatype. But in C++ we do not have such datatype. what should I use in C++ fuction to make the compatibilty with currency datatype?

Answer 1

I guess the best bet is to pass it as a VARIANT and manually handle the VARIANT in the C++ code.

Answer 2

Just take the currency type and multiply it by 100, then pass it to C++ as a long integer. When you needs results back, do the reverse.

There will be no loss of precision, and the code is very simple.

Answer 3

The VB6s currency type is roughly the same as the CY type from C++ (assuming a Microsoft compiler)

Internally it is an 8-byte integer which is scaled by a factor of 10,000, giving you 4 digits after the decimal separator.

Depending on the compiler you can directly use the CY type or pass a VARIANT and use myVariant.cyVal (which is of the CY type).

If you don't have the VARIANT and CY type available (they are not part of the C++ standard) your C++ function has to accept a 64-bit integer and you have to divide the value by 10,000 to get the correct value. (Either use __int64 or long long, again depending on the compiler)

Answer 4

I believe Visual C++ has a native 64-bit integer type __int64 (also known as CY), which is roughly equivalent to VB6 Currency? Although in your C++ code you will "see" the value as 10,000 times larger than the value you "see" in VB6. Either divide by 10,000 in the C++ to get the correct value, or work with the scaled value to keep the precision.

For other C++ compilers Bruce McKinney's bible Hardcore Visual Basic recommends something like this, so does MSDN:

typedef union _LARGE_INTEGER {
    struct {
        DWORD LowPart;
        LONG  HighPart;
    };
    LONGLONG QuadPart;    // In Visual C++, a typedef to __int64
} LARGE_INTEGER;

See here for more details.