Topic: BASS_ChannelGetData returns a DWORD, but also -1?

[ManlioMZ]

I ran into some problems testing the BASS library in Lazarus pascal, because BASS_ChannelGetData returns a result in DWORD format, but the documentation says that in case of errors, the result is -1.

Now, DWORD (at least in Pascal) is an unsigned number, and cannot be -1.

Therefore if I read the result of BASS_ChannelGetData with a DWORD variable, and check for a -1 result, I will never get it!

I solved it by using a signed integer, instead of DWORD, to store the result of the BASS_ChannelGetData call. Alternatively, I check that the unsigned returned number of bytes/samples is within the expected range.

Anyway, problem solved for me, but I thought to let everyone know about this situation. Something similar may also happen with other functions that return DWORD and represent errors with -1

[Ian @ un4seen]

-1 is an integer with all bits set, so the same as FFFFFFFF hex (or FFFFFFFFFFFFFFFF for 64-bit values) but less typing. For Pascal/Delphi, there's a DW_ERROR constant (and QW_ERROR for 64-bit) defined in BASS.PAS that you can use instead. Using "not 0" may also work.

[ManlioMZ]

Thanks, understood. Please note however that "not zero" will not work when I depend on the result of the function to know how many bytes/samples I have received from a call to BASS_ChannelGetData. In that case the non-zero value is the amount of received data, and only the special non-zero case of xFFFFFFFF indicates an error.

[Ian @ un4seen]

I'm not a Pascal/Delphi user myself, so I haven't tried it to confirm, but the "not" keyword can apparently be a logical "not" or a bitwise "not". A bitwise "not 0" will result in -1 (FFFFFFFF). I'm not sure whether "not 0" will work in 64-bit comparisons too or if you would need to modify for that, perhaps "not int64(0)"? May be safest to just stick with the DW_ERROR and QW_ERROR constants.

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