I added a LOG_ON_PTP_E mechanism similar to the LOG_ON_LIBUSB_E one.
This further increases consistency in error reporting in places where
the C_PTP_... macros could not be used. I used the macro mainly where
there have been existing checks for != PTP_RC_OK. There might be a lot
other, yet unchecked places, where this macro could be useful.
I also tuned some of the error/debug messages with the same goal (like
replacing '%x' with '%04x' in the C_PTP_ macros) or adding the
ptp_strerror where appropriate.
Please note, that both the 'inline' and the 'static' keyword in front
of the log_on_ptp_error_helper() function definition are of use here,
to make the compiler not warn about unused functions or functions
without prototype.
git-svn-id: https://svn.code.sf.net/p/gphoto/code/trunk/libgphoto2@15104 67ed7778-7388-44ab-90cf-0a291f65f57c
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