How to get the material names without a .mtl?

[wxfred]

Describe the issue
My model dosen't have a .mtl file, but I need to get the material name for each face. How can I do that?
I tried ObjReader::ParseFromFile, but the size of materials is 0, while there are 8 usemtl in the .obj file.

[syoyo]

I think you can use Load API with Mtl callback. No example code for MTL only callback API though

tinyobjloader/tiny_obj_loader.h

Line 626 in ee45fb4

bool LoadObj(attrib_t *attrib, std::vector<shape_t> *shapes,