Vorbisfile documentation | vorbisfile version 1.3.2 - 20101101

# ov_test_callbacks

declared in "vorbis/vorbisfile.h";

This is an alternative function used to open and test an OggVorbis_File structure when using a data source other than a file, when its necessary to modify default file access behavior, or to test for Vorbis content from a `FILE *` pointer under Windows where ov_test() cannot be used. It allows the application to specify custom file manipulation routines and sets up all the related decoding structures.

Once this has been called, the same `OggVorbis_File` struct should be passed to all the libvorbisfile functions.

    int ov_test_callbacks(void *datasource, OggVorbis_File *vf, char *initial, long ibytes, ov_callbacks callbacks);

### Parameters

f
  File pointer to an already opened file or pipe (it need not be seekable--though this obviously restricts what can be done with the bitstream).
vf
  A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile functions. Once this has been called, the same `OggVorbis_File` struct should be passed to all the libvorbisfile functions.
initial
  Typically set to NULL. This parameter is useful if some data has already been read from the file and the stream is not seekable. It is used in conjunction with `ibytes`. In this case, `initial` should be a pointer to a buffer containing the data read.
ibytes
  Typically set to 0. This parameter is useful if some data has already been read from the file and the stream is not seekable. In this case, `ibytes` should contain the length (in bytes) of the buffer. Used together with `initial`.
callbacks
  A completed ov_callbacks struct which indicates desired custom file manipulation routines. vorbisfile.h defines several preprovided callback sets; see ov_callbacks for details.

### Return Values

> - 0 for success
> - less than zero for failure:
> - OV_EREAD - A read from media returned an error.
> - OV_ENOTVORBIS - Bitstream contains no Vorbis data.
> - OV_EVERSION - Vorbis version mismatch.
> - OV_EBADHEADER - Invalid Vorbis bitstream header.
> - OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.

### Notes

[a] Windows and use as an ov_test() substitute

Windows applications should not use ov_test() due to the likelihood of CRT linking mismatches and runtime protection faults [ov_open:a]. ov_test_callbacks() is a safe substitute; specifically:

    ov_test_callbacks(f, vf, initial, ibytes, OV_CALLBACKS_DEFAULT);

... provides exactly the same functionality as ov_test() but will always work correctly under Windows, regardless of linking setup details.

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Vorbisfile documentation | vorbisfile version 1.3.2 - 20101101