fix: fix bug where multiple fields' structures can only read the first field with mat73

[usopp333]

s.a = [1, 2, 3,4]; s.b=[2,3,4,5];
save('s.mat', 's');

mat_t* matfp = Mat_Open(filename, MAT_ACC_RDONLY);
matvar_t* matvar = Mat_VarReadNext(matfp);
unsigned fields_num = Mat_VarGetNumberOfFields(matvar); // fields_num == 1

• mat73: s.a = [1, 2, 3,4]; s.b=[2,3,4,5]; save('s.mat', 's'); only read s.a;
• mat5: no bug
• fix bug by Cursor-AI
• Update H5Literate return value handling in Mat_H5ReadGroupInfo and Mat_H5ReadGroupInfoIterate functions

[tbeu]

Which tool and version did you use to save the MAT-file? I cannot reproduce the reported issue with the snippet above, because MATLAB R2026a saves a struct's field names in a MATLAB_fields attribute on the struct group. When that attribute is present, matio reads the fields from it (Mat_H5ReadFieldNames), so the H5Literate loop this patch modifies is never executed. The bug therefore only triggers on files without MATLAB_fields, e.g. from other HDF5-based writers.

Reproduction: the issue appears as soon as the attribute is removed. matdump on the MATLAB-saved file reads both fields correctly:

> matdump -d issue321_v73.mat
      Name: s
      Rank: 2
Class Type: Structure
Fields[2] {
1 2 3 4
2 3 4 5
}

After deleting MATLAB_fields from /s, only the first field is read:

> matdump -d issue321_v73_nofields.mat
      Name: s
      Rank: 2
Class Type: Structure
Fields[1] {
1 2 3 4
}

h5dump confirms the two files differ only by that attribute:

> h5dump -n 1 -H issue321_v73.mat
FILE_CONTENTS {
 group      /
 group      /#refs#
 dataset    /#refs#/a
 attribute  /#refs#/a/MATLAB_class
 attribute  /#refs#/a/MATLAB_empty
 group      /s
 attribute  /s/MATLAB_class
 attribute  /s/MATLAB_fields
 dataset    /s/a
 attribute  /s/a/H5PATH
 attribute  /s/a/MATLAB_class
 dataset    /s/b
 attribute  /s/b/H5PATH
 attribute  /s/b/MATLAB_class
 }

> h5dump -n 1 -H issue321_v73_nofields.mat
FILE_CONTENTS {
 group      /
 group      /#refs#
 dataset    /#refs#/a
 attribute  /#refs#/a/MATLAB_class
 attribute  /#refs#/a/MATLAB_empty
 group      /s
 attribute  /s/MATLAB_class
 dataset    /s/a
 attribute  /s/a/H5PATH
 attribute  /s/a/MATLAB_class
 dataset    /s/b
 attribute  /s/b/H5PATH
 attribute  /s/b/MATLAB_class
 }

Could you provide the actual .mat file from your report (or the MATLAB version used)? Note that a regression test would need a v7.3 struct file without MATLAB_fields, since MATLAB-generated files never exercise this code path.

issue321_test_files.zip

[tbeu]

@usopp333 Any feedback?

[usopp333]

Structs.zip

Lum_struct load failed

• Lum_struct version=512 is MAT_FT_MAT73
• Sim_struct version=512 is MAT_FT_MAT73

Matlab 2025b

vscode debugger

• Lum_struct Failed

- Sim_Struct

The version of MATLAB I am using is 2025b

[tbeu]

But which tools created Lum_struct.mat. I doubt it was MATLAB R2025b.