meshioplusplus

<p align="center"> <a href="https://github.com/loumalouomega/meshioplusplus"><img alt="meshio++" src="https://raw.githubusercontent.com/loumalouomega/meshioplusplus/master/doc/logo/logo-with-text.svg" width="60%"></a> <p align="center">I/O for mesh files.</p> </p>

There are various mesh formats available for representing unstructured meshes. meshio++ can read and write all of the following and smoothly converts between them:

Native parity additions: XDMF2/3 and absolute DataItem references; Netgen name/periodic tables, two-line edges and zlib-enabled .vol.gz; PCD compressed writes via MIO_CODEC_LZF / codec="lzf"; and parameterized glTF export in C, Fortran, Julia, R and WASM. See formats, C API and WASM for options and indexing conventions.

Region-backed point/cell sets now convert to and from scalar integer data in the native core, C/Fortran/Julia/R/WASM bindings and native CLI convert -s/-d. Python's mutating Mesh methods preserve their ordering and metadata contract; pipelines expose SetsToData / DataToSets, and MCP exposes sets_data. See sets/data conversions.

Native C/Fortran/Julia/R pipelines also expose owning structured JSON reports (steps and warnings), without replacing their existing status-only entry points; see pipeline reports.

Exodus writers now preserve node/side sets and expose fixed-grid time-series writers across Python, C++, C, Fortran, Julia, R and WASM; sequence fan-in can write one Exodus file. Pipeline schema Version 2 adds file-backed Merge/Interpolate/UndoGreen and terminal Split/Partition with Output.Pattern. Version 1 remains unchanged. See Exodus and pipeline v2.

XDMF time-series writers preserve fixed point, cell and side regions alongside the shared topology. Python's array-based writer accepts regions= and its series reader exposes reader.regions; native writers use the regions already on the mesh. See XDMF time series.

Serial VTK XML readers (.vtu, .vtp, .vts, .vtr, .vti) accept multiple pieces and appended raw/base64 arrays in both the native core and Python reference, with UInt32/UInt64 headers and either byte order. Pieces concatenate without welding; VTP/VTS/VTR/VTI writers remain inline. Native legacy .vtk reads also support structured points, structured grids and rectilinear grids in ASCII and big-endian binary; see the format documentation.

Abaqus (.inp), Abaqus results file (.fil, ASCII and binary, read-only; every increment is a step, nodal and element results by output location), ANSYS Fluent mesh (.msh; cells rebuilt from faces, written face-based as Fluent reads it, zones as named regions), Ansys MAPDL coded database (.cdb, .inp; degenerate shapes resolved, components as named regions) and results (.rst, .rth, read-only; nodal solution, reactions and element nodal stresses, strains and forces, every result set is a step; distributed solves merged, the full rotor of a static cyclic model), AVS-UCD (.avs), CAE sample layout (.npz, what PhysicsNeMo's DoMINO/Transolver datapipes read), CGNS (.cgns), DOLFIN XML (.xml), DOLFINx VTX (.bp, an ADIOS2 directory, read-only; each step a mesh, with an optional ADIOS2 build or the adios2 package), COMSOL mesh (.mphtxt text and .mphbin binary; Selections as named regions, COMSOL's own node order), Exodus (.e, .exo), Elmer mesh directory (mesh.header/.nodes/.elements/.boundary/.names, text or ElmerGrid's binary; bodies and boundaries as named regions, ElmerGrid partitions merged, partition:part written as partitioning.N, recognised by content), EnSight Gold (geometry, .case/.geo; C and Fortran binary), FEBio input (.feb, spec 2.5/3.0/4.0 read, 4.0 written; sets and surfaces as named regions, MeshData read and written) and plot files (.xplt, read-only; every state is a step, remeshed runs included, surface variables on facet blocks), Femap neutral file (.neu, 4.41 to 2020.1 read, 8.2 mesh written; properties and groups as named regions, every output set is a step, a series written as one output set per step), FLAC3D (.f3grid, named cell groups), FLUX (mesh .pf3, field .dex), FreeFem++ (.msh), GiD postprocess (.post.msh/.post.res, .post.bin, .post.h5; writing via a vendored gidpost, reading is meshio++'s own code), H5M (.h5m), Code_Aster native mesh (.mail; GROUP_MA/GROUP_NO as named regions, Code_Aster's own node order), CalculiX results (.frd, ASCII or binary written too; every increment is a step, tensors keep the file order, opt-in von Mises and principal values), HMF (.hmf, experimental, meshio++-specific), IGES (.igs, .iges, read-only, with the optional OpenCASCADE backend; triangulated, with its NURBS B-rep), I-deas Universal / UNV (.unv, .uff), ANSYS Fluent interpolation (.ip), Kratos/MDPA (.mdpa; tables, geometries, Mesh blocks and Constraints, including nested sub-model-part geometry/constraint membership, kept in a side channel on every surface; the Kratos IGA geometry beside a deck loaded with it), Kratos CAD JSON (.cad.json; trimmed NURBS faces, trimming loops and coupling edges for Kratos IGA, sampled as Lagrange cells and kept exactly in a side channel on every surface, and the ImportNurbsSbmModeler dialect), libMesh (.xda, .xdr, also gzip/bzip2; active cells of refined meshes, subdomains, side, edge, shell-face and node sets as named regions, written back in the 1.8.0 layout), LS-DYNA (keyword input .k, .key, .dyn; *PART and *SET_* as named regions, *INCLUDE followed), LS-DYNA d3plot (the binary state database, d3plot and its d3plot01... family, read-only; every state is a step, parts are regions, deletion flags a mask; SPH, airbag particles, rigid bodies and roads), LS-DYNA binout (the LSDA binary output, read-only; nodout outputs are steps, the other databases field data), Medit (.mesh, .meshb), MFEM mesh (.mesh, recognised by content; order-2 curved meshes in MFEM's own numbering, attribute sets as named regions, NURBS meshes with their patches kept and written back) and grid functions (.gf), MED/Salome (.med; native named multi-mesh access and nodal/element profile expansion), Modulef (mesh .mfm, field .mff), Nastran and Altair OptiStruct (bulk data, .bdf, .fem, .nas; HyperMes