C++ numpy format deserializer

readnp.h

#ifndef _READNP_H_
#define  _READNP_H_
// Simple header-only library for loading serialized numpy arrays.
// Only for testing.

#include <algorithm>
#include <cassert>
#include <fstream>
#include <regex>
#include <string>
#include <vector>

template<typename T>
inline void readnp(std::string fn, std::vector<T>& data, std::vector<uint64_t>& shape) {
    static_assert(std::is_same<T, float>::value
               || std::is_same<T, int>::value, "unsupported type");

    static std::string signature = "\x93NUMPY";

    std::ifstream f(fn);
    std::string line;
    std::getline(f, line, '\n');
    //std::cout << "line: " << line << std::endl;
    // many filetypes are handled by np.load, so check it's the right kind:
    assert(std::equal(signature.begin(), signature.end(), line.begin()));

    // double check types:
    if (std::is_same<T, float>::value) { // float == <f4
        assert(std::regex_search(line, std::regex(R"('descr':\s*'<f4')")));
    } else if (std::is_same<T, int>::value) { // int == <i4
        assert(std::regex_search(line, std::regex(R"('descr':\s*'<i4')")));
    }
    assert(std::regex_search(line, std::regex(R"('fortran_order':\s*False)")));

    // get shape:
    std::smatch mat;
    assert(std::regex_search(line, mat, std::regex(R"('shape':\s*\(([\d, ]+)\))")));
    std::string shape_str = mat.str(1);
    //std::cout << "shape = " << shape_str << std::endl;

    assert(shape.empty());
    std::smatch num_match;
    std::regex num_re("\\d+");
    uint64_t nelem = 1;
    while(std::regex_search(shape_str, num_match, num_re)) {
        uint64_t dim = std::stol(num_match.str(0));
        //std::cout << "dim: " << dim << std::endl;
        shape.push_back(dim);
        nelem *= dim;
        shape_str = num_match.suffix();
    }

    // populate data:
    data.resize(nelem);
    f.read(reinterpret_cast<char*>(&data[0]), sizeof(T) * nelem);
}

#endif