What compiler flags does libspotify expect related to packing?

Question

I'm using libspotify 12.1.51 on Windows. While it mostly works as expected, I'm having some difficulty with sp_offline_sync_status:

typedef struct sp_offline_sync_status {
  int queued_tracks;
  sp_uint64 queued_bytes;

  int done_tracks;
  sp_uint64 done_bytes;

  int copied_tracks;
  sp_uint64 copied_bytes;

  int willnotcopy_tracks;

  int error_tracks;
  bool syncing;

} sp_offline_sync_status;

(sp_uint64 is a typedef for an unsigned __int64 on Windows and uint64_t otherwise. When building in C (not C++) and if bool is not otherwise defined, it is a typedef for unsigned char.)

When I call sp_offline_sync_get_status, only queued_tracks seems to have correct data, the rest is garbage. However, if I edit the header file to include #pragma pack(1), it seems to give more plausible results. I observe this behaviour even when I try to build the spshell example that comes with libspotify.*

This leads me to believe that the libspotify binary is compiled with some different compiler flags from the defaults, at least on Windows with Visual C++. How should I be compiling C or C++ code to use libspotify? Or should I use #pragma pack before #including api.h and then restore it back? Can I expect this to remain stable in future versions of libspotify or is it likely to change? How does it vary across platforms?

My true goal is to write C# P/Invoke code, that works on a variety of platforms using Mono. On non-Windows platforms does libspotify stick to the default alignment for the native compiler, or will I need to specify custom alignment on each platform?

[*] - I did have to fix some other bugs first, though. As provided in libspotify 12.1.51, on Windows spshell registers control key-presses (e.g. shift, ctrl) as typing a NUL character. This prevents typing or pasting spotify URIs into the console. This can be fixed by editing spshell_win32.c to add case 0: break; to the switch statement in console_input. Also, it uses the string format specifier "%zd" in spshell.c in the function offline_status_updated. The Microsoft C runtime doesn't seem to handle this, so it needs to be changed (e.g. to "%Iu" if you only want it to work on Windows, or to a platform-sensitive macro).

Answer 1

libspotify is compiled with '-Zp4' whereas standard appears to be '-Zp8'. I guess one could either compile with that flag, or use the #pragma pack(4) directive (I actually think 4 is more correct than 1, as you used in your question)

Will put a note in Jira to fix the errors in spshell.c you pointed out. Thanks!