[Vxl-users] suppressing/redirecting errors from vsl?

[Matthew W. <mat...@ki...>]

I am writing a file reader that tries to read data from a VSL stream of 
unknown format. Since there is no eyecatcher or other identifying mark 
in the file, the only way I know of to do this is to attempt to read the 
data and watch for failures, and use that to guess what type of file I 
am dealing with. (Fortunately the possible data layouts are such that it 
is unlikely that trying to read one type of file as the wrong type will 
succeed.)

This seems like a reasonable approach, but it is VERY noisy due to a 
bunch of output that VSL spews to stderr. Since I am doing speculative 
reads, I expect there is a good chance they will fail, and that this is 
not an error and should not spam the user's console output.

I could use dup2 to monkey around with stderr, but this is not a good 
thing to be doing in a library and in a multi-threaded context.

Would it be reasonable to patch vsl_b_istream and the various vsl_b_read 
such that the user can specify a different output stream to use for 
outputting such error messages? (I'm thinking to set a std::ostream* on 
the vsl_b_istream to use for error output; the default would be 
&vcl_cerr. The caller would be responsible for correctly managing the 
life cycle of the std::ostream object.)

-- 
Matthew