VFS crash (basic_string: construction from null is not valid) when directory is NULL.

[davidhozic]

Intro

Hi!

I am a graduate student at University of Ljubljana, I use MuJoCo for RL.

My setup

MuJoCo 3.3.5, C API, x86_64, Ubuntu 24.04.3 LTS (Kubuntu).

What's happening? What did you expect?

When trying to add a real file to the virtual file system and the directory is given argument NULL, an exception basic_string: construction from null is not valid is thrown,
before crashing.

Based on the documentation, the directory parameter is allowed to be NULL:

mj_addFileVFS
int mj_addFileVFS(mjVFS* vfs, const char* directory, const char* filename);
Add file to VFS. The directory argument is optional and can be NULL or empty. Returns 0 on success, 2 on name collision, or -1 when an internal error occurs.

Nullable: directory

Steps for reproduction

Try to pass NULL as the directory parameter in mj_addFileVFS.

Minimal model for reproduction

No model is used.

Code required for reproduction

int main(int argc, char** argv) {

    mjVFS vfs;
    mj_defaultVFS(&vfs);

    mj_addFileVFS(&vfs, NULL, "test.c");

    mj_deleteVFS(&vfs);

    return 0;
}

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.