Implementation:Google deepmind Mujoco mj loadXML

Knowledge Sources	MuJoCo MuJoCo API Reference
Domains	Physics_Simulation, Model_IO
Last Updated	2026-02-15 06:00 GMT

Overview

Concrete tool for loading and compiling MuJoCo models from MJCF XML or URDF files provided by the MuJoCo C API.

Description

The mj_loadXML function is the primary entry point for loading MuJoCo models. It parses an XML model file (MJCF or URDF), compiles it into an mjModel structure, and returns a pointer to the compiled model. Internally, it calls ParseXML to build a specification tree, then mj_compile to produce the runtime model. An optional Virtual File System (VFS) allows loading resources from memory rather than disk.

Usage

Use this function at the start of any MuJoCo simulation to load a model from an XML file. This is the standard entry point for both MJCF and URDF formats.

Code Reference

Source Location

• Repository: mujoco
• File: src/xml/xml_api.cc
• Lines: 40-70

Signature

mjModel* mj_loadXML(const char* filename, const mjVFS* vfs,
                    char* error, int error_sz);

Import

#include <mujoco/mujoco.h>

I/O Contract

Inputs

Name	Type	Required	Description
filename	const char*	Yes	Path to MJCF XML or URDF model file
vfs	const mjVFS*	No	Virtual file system for in-memory resources (NULL for disk)
error	char*	No	Buffer for error/warning messages (NULL to skip)
error_sz	int	No	Size of error buffer in bytes

Outputs

Name	Type	Description
return	mjModel*	Compiled physics model (NULL on failure)
error	char*	Populated with error or warning message if applicable

Usage Examples

Basic Model Loading

#include <mujoco/mujoco.h>

// Load model from XML file
char error[1000] = "";
mjModel* m = mj_loadXML("humanoid.xml", NULL, error, 1000);
if (!m) {
    printf("Load error: %s\n", error);
    return 1;
}

// Use the model...

// Cleanup
mj_deleteModel(m);

Loading with Virtual File System

#include <mujoco/mujoco.h>

// Create and populate VFS
mjVFS vfs;
mj_defaultVFS(&vfs);
mj_addFileVFS(&vfs, ".", "model.xml");

// Load from VFS
char error[1000] = "";
mjModel* m = mj_loadXML("model.xml", &vfs, error, 1000);

// Cleanup
mj_deleteVFS(&vfs);
if (m) mj_deleteModel(m);

Related Pages

Implements Principle

• Principle:Google_deepmind_Mujoco_Model_Loading

Requires Environment

• Environment:Google_deepmind_Mujoco_C_Build_Environment