TIFFWARNING(3tiff) LibTIFF TIFFWARNING(3tiff)

TIFFWarning - library warning interface

#include <tiffio.h>
#include <stdarg.h>

TIFFWarning() invokes the library-wide warning handler function to (normally) write a warning message to the stderr. The fmt parameter is a printf() format string, and any number arguments can be supplied. The module parameter is interpreted as a string that, if non-zero, should be printed before the message; it typically is used to identify the software module in which a warning is detected.

Applications that desire to capture control in the event of a warning should use TIFFSetWarningHandler() to override the default warning handler. A NULL (0) warning handler function may be installed to suppress warning messages.

Two more application-specific warning handler callbacks are available, each with different call parameters and passing parameters to the handler. Each handler is also linked with a warning message function, i.e. TIFFWarningExt() and TIFFWarningExtR() if the application intends to call the handler with those extended parameters.

TIFFWarningExt() provides a file handle as parameter. Within libtiff TIFFWarningExt() is called passing tif->tif_clientdata as fd, which represents the TIFF file handle (file descriptor). The application-specific and library-wide handler for TIFFWarningExt() is setup with TIFFSetWarningHandlerExt().

TIFFWarningExtR() (introduced with libtiff 4.5) is called with its TIFF handle and thus provides access to a per-TIFF handle (re-entrant) warning handler. That means for different TIFF handles, different warning handlers can be setup. This application-specific handler can be setup when a TIFF file is opened with one of the following functions: TIFFOpenExt(), TIFFOpenWExt(), TIFFFdOpenExt() or TIFFClientOpenExt(). Furthermore, a custom defined data structure user_data for the warning handler can be given along.

Both functions TIFFWarning() and TIFFWarningExt() each attempt to call both handler functions if they are defined. First TIFFWarningHandler() is called and then TIFFWarningHandlerExt(). However, TIFFWarning() passes a “0” as a file handle to TIFFWarningHandlerExt().

TIFFWarningExtR() tries first to call the per-TIFF handle defined warning handler. If TIFFWarningHandlerExtR() is not defined or returns 0, TIFFWarningHandler() and then TIFFWarningHandlerExt() are called. From libtiff 4.5 onwards TIFFWarningExtR() is used within the libtiff library.

TIFFSetWarningHandler() and TIFFSetWarningHandlerExt() returns a reference to the previous warning handler function.

TIFFWarningHandlerExtR() returns an integer as “stop” to control the call of furhter warning handler functions within TIFFWarningExtR():

  • 0: both functions TIFFWarningHandler() and TIFFWarningHandlerExt() are called.
  • non-zero: no further warning message function is called.

TIFFError (3tiff), TIFFOpen (3tiff), libtiff (3tiff), printf (3)

LibTIFF contributors

1988-2022, LibTIFF contributors

September 8, 2023 4.6