Single-header C++ (header-only)

The whole meshio++ C++ core is also available as one self-contained header, single_include/meshioplusplus/meshioplusplus.hpp. Drop it into any project — no CMake, no submodules, nothing to link (unless you opt into the optional formats below). It follows the well-known STB single-file-library convention:

// in exactly ONE .cpp of your project — pulls in all the implementations:
#define MESHIOPLUSPLUS_IMPLEMENTATION
#include "meshioplusplus/meshioplusplus.hpp"

// in every other translation unit — declarations only:
#include "meshioplusplus/meshioplusplus.hpp"

The header bundles pugixml (MIT), so the XML-based formats (VTU, XDMF-XML, DOLFIN) work out of the box.

Example

#define MESHIOPLUSPLUS_IMPLEMENTATION
#include "meshioplusplus/meshioplusplus.hpp"
#include <cstring>
using namespace meshioplusplus;

int main() {
    Mesh m;
    NDArray points(DType::Float64, {3, 3});
    double xyz[9] = {0,0,0, 1,0,0, 0,1,0};
    std::memcpy(points.Data(), xyz, sizeof(xyz));
    m.AssignPoints(std::move(points));

    NDArray conn(DType::Int64, {1, 3});
    long long tri[3] = {0, 1, 2};
    std::memcpy(conn.Data(), tri, sizeof(tri));
    m.AddCellBlock("triangle", std::move(conn));

    registry_writers().at("stl")("mesh.stl", m);       // write
    Mesh back = registry_readers().at("stl")("mesh.stl");   // read back
    return 0;
}

g++ -std=c++20 -I single_include main.cpp -o main

The public surface is the same uniform mesh API and format registry the rest of the C++ core uses: registry_readers() / registry_writers() (name -> function), resolve_format(path, ""), plus the Mesh type and the ReadError / WriteError exceptions.

Configuration macros

Everything defaults to a zero-dependency build. Define these before including the header to change that:

Macro	Effect
(none)	Mesh backend MESHIO, sequential parallel backend, no external libraries.
MESHIOPLUSPLUS_MESH_BACKEND_NATIVE / _KRATOS	Select a different mesh backend.
MESHIOPLUSPLUS_PARALLEL_OPENMP / _TBB / _STL	Enable a parallel backend (and link/compile with the matching flags).
MESHIOPLUSPLUS_HAS_ZLIB	VTU zlib compression — also link -lz.
MESHIOPLUSPLUS_HAS_HDF5	CGNS / HMF / H5M / MED / XDMF-HDF — also link -lhdf5.
MESHIOPLUSPLUS_HAS_NETCDF	Exodus — also link -lnetcdf.
MESHIOPLUSPLUS_HAS_EIGEN	Faster MED transpose — add Eigen to the include path.

Optional-dependency code stays behind its MESHIOPLUSPLUS_HAS_* guard, so the default include compiles with no third-party libraries at all — the same format set as the WebAssembly build.

How it is generated

The single header is generated from the sources under cpp/ by tools/amalgamate.sh (which drives tools/amalgamate/amalgamate.py) and committed to the repo. CI regenerates it on every push and fails if the committed copy is stale, then smoke-compiles it (declarations-only, MESHIOPLUSPLUS_IMPLEMENTATION, and a two-TU link). Do not edit the generated file by hand — edit the sources under cpp/ and run:

./tools/amalgamate.sh          # regenerate single_include/…/meshioplusplus.hpp
./tools/amalgamate.sh --smoke  # regenerate + smoke-compile

The generator emits every header once, at file scope, in dependency order (so a header can never be trapped inside another's #ifdef), then the .cpp bodies under a single MESHIOPLUSPLUS_IMPLEMENTATION guard.