Is there any special consideration/limitation that multi-dimensional C-style array member of struct is not supported?

[peng-wang-cn]

Hi, @nlohmann,

I'm trying to use the library for a struct with multi-dimensional (C-style) array member, like:

struct struct1 {
  int m1;
  int m2[4];
  int m3[2][3];

public:
  NLOHMANN_DEFINE_TYPE_INTRUSIVE(struct1, m1, m2, m3)
};

The compiler (I'm using g++ 11.4) spits errors complaining:

.../json.cpp:2745:62: error: no matching function for call to 'nlohmann::json_abi_v3_11_3::basic_json<>::get_to(int [2][3]) const'

If m3 is removed, everything is OK.

Is it possible that multi-dimensional array members are supported? Or is there any special limitation that prevent it from being supported?

Thanks,
Peng

[peng-wang-cn]

Hi, there,

I'd figured out that by adding new version of from_json() for T (&arr)[N1][N2] it will support 2-dimensional array.
However one caveat of it is separate versions of from_json() need to be added for 3 and 4 dimensional arrays etc.
@nlohmann If you think this approach is OK, I could submit a pull request for it. I think we should also document the highest dimension supported.
BTW, for multi-dimensional arrays, if pretty_print switch is on, each value of the inner most dimension array will also be printed in separate lines, which is not very readable. My suggestion is for the inner most dimension, each array should be printed in a whole line. How do you think about it?

Thanks,
Peng

[peng-wang-cn]

@nlohmann ,

What version of astyle should I use for amalgamation? I'm using 3.4.10, and I'm getting some blank-space-only changes.

Thanks,
Peng

[nlohmann]

Please use version 3.1

[peng-wang-cn]

I downgraded to astyle 3.1, but 'make amalgamate' complains about invalid command line option 'squeeze-lines=2' of astyle:

/mnt/d/github/nlohmann-json/ws00$ make amalgamate
tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json.json -s . --verbose=yes
Config:
 target        = single_include/nlohmann/json.hpp
 working_dir   = /mnt/d/github/nlohmann-json/ws00
 include_paths = ['include']
Creating amalgamation:
 - processing "include/nlohmann/json.hpp"
...done!

Files processed: ['include/nlohmann/json.hpp']
Files included: ['include/nlohmann/json.hpp', 'include/nlohmann/adl_serializer.hpp', 'include/nlohmann/detail/abi_macros.hpp', 'include/nlohmann/detail/conversions/from_json.hpp', 'include/nlohmann/detail/exceptions.hpp', 'include/nlohmann/detail/value_t.hpp', 'include/nlohmann/detail/macro_scope.hpp', 'include/nlohmann/detail/meta/detected.hpp', 'include/nlohmann/detail/meta/void_t.hpp', 'include/nlohmann/thirdparty/hedley/hedley.hpp', 'include/nlohmann/detail/string_escape.hpp', 'include/nlohmann/detail/input/position_t.hpp', 'include/nlohmann/detail/meta/cpp_future.hpp', 'include/nlohmann/detail/meta/type_traits.hpp', 'include/nlohmann/detail/iterators/iterator_traits.hpp', 'include/nlohmann/detail/meta/call_std/begin.hpp', 'include/nlohmann/detail/meta/call_std/end.hpp', 'include/nlohmann/json_fwd.hpp', 'include/nlohmann/detail/string_concat.hpp', 'include/nlohmann/detail/meta/identity_tag.hpp', 'include/nlohmann/detail/meta/std_fs.hpp', 'include/nlohmann/detail/conversions/to_json.hpp', 'include/nlohmann/detail/iterators/iteration_proxy.hpp', 'include/nlohmann/byte_container_with_subtype.hpp', 'include/nlohmann/detail/hash.hpp', 'include/nlohmann/detail/input/binary_reader.hpp', 'include/nlohmann/detail/input/input_adapters.hpp', 'include/nlohmann/detail/input/json_sax.hpp', 'include/nlohmann/detail/input/lexer.hpp', 'include/nlohmann/detail/meta/is_sax.hpp', 'include/nlohmann/detail/input/parser.hpp', 'include/nlohmann/detail/iterators/internal_iterator.hpp', 'include/nlohmann/detail/iterators/primitive_iterator.hpp', 'include/nlohmann/detail/iterators/iter_impl.hpp', 'include/nlohmann/detail/iterators/json_reverse_iterator.hpp', 'include/nlohmann/detail/json_custom_base_class.hpp', 'include/nlohmann/detail/json_pointer.hpp', 'include/nlohmann/detail/json_ref.hpp', 'include/nlohmann/detail/output/binary_writer.hpp', 'include/nlohmann/detail/output/output_adapters.hpp', 'include/nlohmann/detail/output/serializer.hpp', 'include/nlohmann/detail/conversions/to_chars.hpp', 'include/nlohmann/ordered_map.hpp', 'include/nlohmann/detail/macro_unscope.hpp', 'include/nlohmann/thirdparty/hedley/hedley_undef.hpp']

tools/amalgamate/amalgamate.py -c tools/amalgamate/config_json_fwd.json -s . --verbose=yes
Config:
 target        = single_include/nlohmann/json_fwd.hpp
 working_dir   = /mnt/d/github/nlohmann-json/ws00
 include_paths = ['include']
Creating amalgamation:
 - processing "include/nlohmann/json_fwd.hpp"
...done!

Files processed: ['include/nlohmann/json_fwd.hpp']
Files included: ['include/nlohmann/json_fwd.hpp', 'include/nlohmann/detail/abi_macros.hpp']

make pretty
make[1]: Entering directory '/mnt/d/github/nlohmann-json/ws00'
astyle \
    --style=allman \
    --indent=spaces=4 \
    --indent-modifiers \
    --indent-switches \
    --indent-preproc-block \
    --indent-preproc-define \
    --indent-col1-comments \
    --pad-oper \
    --pad-header \
    --align-pointer=type \
    --align-reference=type \
    --add-braces \
    --squeeze-lines=2 \
    --convert-tabs \
    --close-templates \
    --lineend=linux \
    --preserve-date \
    --suffix=none \
    --formatted \
   include/nlohmann/adl_serializer.hpp include/nlohmann/byte_container_with_subtype.hpp include/nlohmann/detail/abi_macros.hpp include/nlohmann/detail/conversions/from_json.hpp include/nlohmann/detail/conversions/to_chars.hpp include/nlohmann/detail/conversions/to_json.hpp include/nlohmann/detail/exceptions.hpp include/nlohmann/detail/hash.hpp include/nlohmann/detail/input/binary_reader.hpp include/nlohmann/detail/input/input_adapters.hpp include/nlohmann/detail/input/json_sax.hpp include/nlohmann/detail/input/lexer.hpp include/nlohmann/detail/input/parser.hpp include/nlohmann/detail/input/position_t.hpp include/nlohmann/detail/iterators/internal_iterator.hpp include/nlohmann/detail/iterators/iter_impl.hpp include/nlohmann/detail/iterators/iteration_proxy.hpp include/nlohmann/detail/iterators/iterator_traits.hpp include/nlohmann/detail/iterators/json_reverse_iterator.hpp include/nlohmann/detail/iterators/primitive_iterator.hpp include/nlohmann/detail/json_custom_base_class.hpp include/nlohmann/detail/json_pointer.hpp include/nlohmann/detail/json_ref.hpp include/nlohmann/detail/macro_scope.hpp include/nlohmann/detail/macro_unscope.hpp include/nlohmann/detail/meta/call_std/begin.hpp include/nlohmann/detail/meta/call_std/end.hpp include/nlohmann/detail/meta/cpp_future.hpp include/nlohmann/detail/meta/detected.hpp include/nlohmann/detail/meta/identity_tag.hpp include/nlohmann/detail/meta/is_sax.hpp include/nlohmann/detail/meta/std_fs.hpp include/nlohmann/detail/meta/type_traits.hpp include/nlohmann/detail/meta/void_t.hpp include/nlohmann/detail/output/binary_writer.hpp include/nlohmann/detail/output/output_adapters.hpp include/nlohmann/detail/output/serializer.hpp include/nlohmann/detail/string_concat.hpp include/nlohmann/detail/string_escape.hpp include/nlohmann/detail/value_t.hpp include/nlohmann/json.hpp include/nlohmann/json_fwd.hpp include/nlohmann/ordered_map.hpp include/nlohmann/thirdparty/hedley/hedley.hpp include/nlohmann/thirdparty/hedley/hedley_undef.hpp tests/abi/config/config.hpp tests/abi/config/custom.cpp tests/abi/config/default.cpp tests/abi/config/noversion.cpp tests/abi/diag/diag.cpp tests/abi/diag/diag.hpp tests/abi/diag/diag_off.cpp tests/abi/diag/diag_on.cpp tests/abi/inline_ns/use_current.cpp tests/abi/inline_ns/use_v3_10_5.cpp tests/abi/main.cpp tests/benchmarks/src/benchmarks.cpp tests/cmake_add_subdirectory/project/main.cpp tests/cmake_fetch_content/project/main.cpp tests/cmake_fetch_content2/project/main.cpp tests/cmake_import/project/main.cpp tests/cmake_import_minver/project/main.cpp tests/cmake_target_include_directories/project/Bar.cpp tests/cmake_target_include_directories/project/Bar.hpp tests/cmake_target_include_directories/project/Foo.cpp tests/cmake_target_include_directories/project/Foo.hpp tests/cmake_target_include_directories/project/main.cpp tests/cuda_example/json_cuda.cu tests/src/fuzzer-driver_afl.cpp tests/src/fuzzer-parse_bjdata.cpp tests/src/fuzzer-parse_bson.cpp tests/src/fuzzer-parse_cbor.cpp tests/src/fuzzer-parse_json.cpp tests/src/fuzzer-parse_msgpack.cpp tests/src/fuzzer-parse_ubjson.cpp tests/src/make_test_data_available.hpp tests/src/test_utils.hpp tests/src/unit-32bit.cpp tests/src/unit-algorithms.cpp tests/src/unit-allocator.cpp tests/src/unit-alt-string.cpp tests/src/unit-assert_macro.cpp tests/src/unit-binary_formats.cpp tests/src/unit-bjdata.cpp tests/src/unit-bson.cpp tests/src/unit-byte_container_with_subtype.cpp tests/src/unit-capacity.cpp tests/src/unit-cbor.cpp tests/src/unit-class_const_iterator.cpp tests/src/unit-class_iterator.cpp tests/src/unit-class_lexer.cpp tests/src/unit-class_parser.cpp tests/src/unit-comparison.cpp tests/src/unit-concepts.cpp tests/src/unit-constructor1.cpp tests/src/unit-constructor2.cpp tests/src/unit-convenience.cpp tests/src/unit-conversions.cpp tests/src/unit-custom-base-class.cpp tests/src/unit-deserialization.cpp tests/src/unit-diagnostics.cpp tests/src/unit-disabled_exceptions.cpp tests/src/unit-element_access1.cpp tests/src/unit-element_access2.cpp tests/src/unit-hash.cpp tests/src/unit-inspection.cpp tests/src/unit-items.cpp tests/src/unit-iterators1.cpp tests/src/unit-iterators2.cpp tests/src/unit-json_patch.cpp tests/src/unit-json_pointer.cpp tests/src/unit-large_json.cpp tests/src/unit-merge_patch.cpp tests/src/unit-meta.cpp tests/src/unit-modifiers.cpp tests/src/unit-msgpack.cpp tests/src/unit-no-mem-leak-on-adl-serialize.cpp tests/src/unit-noexcept.cpp tests/src/unit-ordered_json.cpp tests/src/unit-ordered_map.cpp tests/src/unit-pointer_access.cpp tests/src/unit-readme.cpp tests/src/unit-reference_access.cpp tests/src/unit-regression1.cpp tests/src/unit-regression2.cpp tests/src/unit-serialization.cpp tests/src/unit-testsuites.cpp tests/src/unit-to_chars.cpp tests/src/unit-type_traits.cpp tests/src/unit-ubjson.cpp tests/src/unit-udl.cpp tests/src/unit-udt.cpp tests/src/unit-udt_macro.cpp tests/src/unit-unicode1.cpp tests/src/unit-unicode2.cpp tests/src/unit-unicode3.cpp tests/src/unit-unicode4.cpp tests/src/unit-unicode5.cpp tests/src/unit-user_defined_input.cpp tests/src/unit-windows_h.cpp tests/src/unit-wstring.cpp tests/src/unit.cpp single_include/nlohmann/json.hpp single_include/nlohmann/json_fwd.hpp docs/examples/*.cpp
Invalid command line options:
        squeeze-lines=2
For help on options type 'astyle -h'
Artistic Style has terminated

make[1]: *** [Makefile:147: pretty] Error 1
make[1]: Leaving directory '/mnt/d/github/nlohmann-json/ws00'
make: *** [Makefile:175: amalgamate] Error 2
/mnt/d/github/nlohmann-json/ws00$ astyle --version
Artistic Style Version 3.1
/mnt/d/github/nlohmann-json/ws00$ astyle -h | grep squeeze
/mnt/d/github/nlohmann-json/ws00$

Grepping astyle -h for 'squeeze' shows nothing.
Any ideas?

Thanks,
Peng

[nlohmann]

Just drop the line --squeeze-lines=2 \. Sorry for the mess. I am currently fighting hard to get rid of astyle, but apparently Clang-Format is even worse (see #4226).

[huqin-RM]

void Dimensions(const json& j, std::vector<int> &v)
{
    int n = 0;
    json tmp;
    for(auto it : j)
    {
        n++;
        tmp = it;
    }

    if(tmp.is_array())
    {
        Dimensions(tmp, v);
    }
    v.push_back(n);
}

template<typename T>
void ProcData(const json& j, std::vector<T> &v)
{
    for(auto it : j)
    {
        if(it.is_array())
        {
            ProcData(it, v);
        }else
        {
            T tmp = it.get<T>();
            v.push_back(tmp);
        }
    }
}

template<typename T>
void PrcoArray(T value, const json& j, void *c, int size) {
    std::vector<T> data;
    ProcData(j, data);
    memcpy(c,data.data(), size);
}

template<typename T>
void PrcoArray(T arr[], const json& j, void *c, int size) {
    PrcoArray(arr[0], j,c, size); // 递归调用
}

namespace nlohmann
{
template<typename T>
void from_json(const json& j, T *c) {
    std::cout << "HUHU " << typeid (T).name() << " " << typeid (c).name() << std::endl;
    int size = 1;
    std::vector<int> Dim;
    Dimensions(j, Dim);
    for(auto it : Dim)
    {
        size *= it;
    }
    PrcoArray(&c, j,c,size);
}

void from_json(const json& j, double *c) {
    std::cout << "QINQIN" << std::endl;
    int size = 1;
    std::vector<int> Dim;
    Dimensions(j, Dim);
    for(auto it : Dim)
    {
        size *= it;
    }
    PrcoArray(c, j,c,size);
}
}

This solves the multi-dimensional problem, but it causes the one-dimensional problem to fail. I'm not sure why.

[nlohmann]

Will be addressed by merging #4262.