Truncated feature names when loaded booster loaded from a file

[geohardtke]

Hi there!
First of all thanks for writing this awsome crate!

I just run into a problem. When loading a model from a file, the feature names get truncated to a n_features -1 length (i.e if I have 3 features, the names get truncated to 2 characters.)
I'm trying to fix the issue myself and if I can, I submit a PR :). But I'm new to rust, and not very good with C, so I'm not sure I'll be able to fix it. The problem must be around like 173 in booster.rs

[geohardtke]

I think I've got it, I think you swapped num_features and feature_name_length when you call LGBM_BoosterGetFeatureNames. The call is currently:

        lgbm_call!(lightgbm_sys::LGBM_BoosterGetFeatureNames(
            self.handle,
            feature_name_length as i32,
            &mut num_feature_names,
            num_feature as u64,
            &mut out_buffer_len,
            out_strs.as_ptr() as *mut *mut c_char
        ))?;

but should be (c api as comment for reference)

        lgbm_call!(lightgbm_sys::LGBM_BoosterGetFeatureNames(
            self.handle,
            num_feature as i32, // len: Number of char* pointers stored at out_strs. If smaller than the max size, only this many strings are copied
            &mut num_feature_names, //  [out] num_feature_names: Number of feature names
            feature_name_length as u64, //buffer_len: Size of pre-allocated strings. Content is copied up to buffer_len - 1 and null-terminated
            &mut out_buffer_len,//
            out_strs.as_ptr() as *mut *mut c_char
        ))?;

Let me know if you want me to make a PR or would it be easier to fix it yourself.

Cheers!

[vaaaaanquish]

@geohardtke Thanks. This issue can indeed be reproduced.
If you available for PR, I wait from you!:)