json_array_arg in not defined

[Priyaankaa13]

Hai.,
json image_formats(json_array_arg, {"JPEG","PSD","TIFF","DNG"});

I used the above statement to create a new array in visual studio but ended up having json_array_arg in not defined exception, since i'm new to this, can anyone pls help me in this ?

[danielaparker]

json_array_arg is in the jsoncons namespace, so you could write

#include <jsoncons/json.hpp>

int main()
{
    jsoncons::json image_formats(jsoncons::json_array_arg, { "JPEG","PSD","TIFF","DNG" });
}

or as often in the examples

#include <jsoncons/json.hpp>

using jsoncons::json;

int main()
{
    json image_formats(jsoncons::json_array_arg, { "JPEG","PSD","TIFF","DNG" });
}

[Priyaankaa13]

Thanks alot

[Priyaankaa13]

Hai., how can i create a array of objects for an particular key, which is values are need to be in array , can you suggest some ideas pls !!

{"Projects":[
{
"project_id": 4001,
"task_name": "task1",
"task_start": "01/01/2003",
"task_finish": "01/31/2003"
},
{
"project_id": 4001,
"task_name": "task2",
"task_start": "02/01/2003",
"task_finish": "02/28/2003"
},
{
"project_id": 4001,
"task_name": "task3",
"task_start": "03/01/2003",
"task_finish": "03/31/2003"
},
{
"project_id": 4002,
"task_name": "task1",
"task_start": "04/01/2003",
"task_finish": "04/30/2003"
},
{
"project_id": 4002,
"task_name": "task2",
"task_start": "05/01/2003"
}
]
}

[danielaparker]

You can construct a jsoncons::json value in a variety of ways and serialize it to a string or stream,

#include <jsoncons/json.hpp>

using json = jsoncons::json;

int main()
{
    json root;  // default is empty object
    json projects(jsoncons::json_array_arg);  // constructs an array with no elements

    {
        json project;
        project.try_emplace("project_id", 4001); 
        project.try_emplace("task_name", "task1"); 
        project.try_emplace("task_start", "01/01/2003"); 
        project.try_emplace("task_finish", "01/31/2003");
        // move project into projects array (more efficient)
        projects.push_back(std::move(project)); 
    }
    {
        json project;
        project.try_emplace("project_id", 4001); 
        project.try_emplace("task_name", "task2"); 
        project.try_emplace("task_start", "02/01/2003"); 
        project.try_emplace("task_finish", "02/28/2003");
        // copy project into projects array (less efficient)
        projects.push_back(project); 
    }
    {
        // or use insert_or_assign, see docs for difference
        json project;
        project.insert_or_assign("project_id", 4001); 
        project.insert_or_assign("task_name", "task3"); 
        project.insert_or_assign("task_start", "03/01/2003"); 
        project.insert_or_assign("task_finish", "03/31/2003");
        projects.push_back(std::move(project)); 
    }
    {
        // or use operator[]
        json project;
        project["project_id"] =  4002; 
        project["task_name"] =  "task1"; 
        project["task_start"] =  "04/01/2003"; 
        project["task_finish"] =  "04/30/2003";
        projects.push_back(std::move(project)); 
    }
    {
        // or
        projects.push_back(json(jsoncons::json_object_arg,
            {{"project_id", 4002},{"task_name", "task2"},{"task_start", "05/01/2003"}}));
    }

    root.try_emplace("Projects", std::move(projects));
    // or with copy, root.try_emplace("Projects", projects);
    // or, root["Projects"] = std::move(projects);
    // or with copy, root["Projects"] = projects;

    std::cout << pretty_print(root) << "\n\n";
}

Or, you can construct a C++ data structure and serialize it to a string or stream.

#include <jsoncons/json.hpp>
#include <optional> // For std::optional, assuming C++17, otherwise use jsoncons::optional
#include <vector>
#include <map>

struct Project
{
    std::size_t project_id;
    std::string task_name;
    std::string task_start;
    std::optional<std::string> task_finish;
};

using Projects = std::map<std::string,std::vector<Project>>;

// The first three data members are mandatory, task_finish is optional
JSONCONS_N_MEMBER_TRAITS(Project,3,project_id,task_name,task_start,task_finish)

int main()
{
    Projects projects;
    std::vector<Project> v;

    v.push_back({4001,"task1","01/01/2003","01/31/2003"});
    v.push_back({4001,"task2","02/01/2003","02/28/2003"});
    v.push_back({4001,"task3","03/01/2003","03/31/2003"});
    v.push_back({4002,"task1","04/01/2003","04/30/2003"});
    v.push_back({4002,"task2","05/01/2003"});

    projects.try_emplace("Projects", v);

    std::string output;
    jsoncons::encode_json_pretty(projects, output);
    std::cout << output << "\n\n";
}

Both of these approaches give

{
    "Projects": [
        {
            "project_id": 4001,
            "task_finish": "01/31/2003",
            "task_name": "task1",
            "task_start": "01/01/2003"
        },
        {
            "project_id": 4001,
            "task_finish": "02/28/2003",
            "task_name": "task2",
            "task_start": "02/01/2003"
        },
        {
            "project_id": 4001,
            "task_finish": "03/31/2003",
            "task_name": "task3",
            "task_start": "03/01/2003"
        },
        {
            "project_id": 4002,
            "task_finish": "04/30/2003",
            "task_name": "task1",
            "task_start": "04/01/2003"
        },
        {
            "project_id": 4002,
            "task_name": "task2",
            "task_start": "05/01/2003"
        }
    ]
}

Note that the name-value pairs appear in sorted order in the output. If it's important to you that the name-value pairs appear in original order, you can use jsoncons::ojson instead of jsoncons::json.

[Priyaankaa13]

Thanks alot for replying, i can understand the concepts you have given but my question is ,
`//creating a JSON
json image_sizing[5];

//values in project_no

int project_no[5] = [1,2,3,4,5];
std::String project_name[5] = ['XXX','YYY','ZZZ','PPP','RRR']
//assiging values with for loop
for (i = 1;i <= 5;i++) {
image_sizing[i].insert_or_assign("Project Number", project_no[i]);
image_sizing[i].insert_or_assign("Project Name", project_name[i]);

                    }

`

then how can make it as a json ?
{
"Projects": [
{
"Project Number": 1,
"Project Name":XXX
},
{
"Project Number": 2,
"Project Name":YYY
},
{
"Project Number": 3,
"Project Name":ZZZ
},
{
"Project Number": 4,
"Project Name":PPP
},
{
"Project Number": 5,
"Project Name":RRR
}
]
}

can you reply pls?

[danielaparker]

Like this,

#include <jsoncons/json.hpp>

using jsoncons::json;

int main()
{
    json image_sizing[5];

    int project_no[5] = { 1, 2, 3, 4, 5 };
    std::string project_name[5] = {"XXX", "YYY", "ZZZ", "PPP", "RRR"};
    for (std::size_t i = 0; i < 5; ++i) 
    {
        image_sizing[i].insert_or_assign("Project Number", project_no[i]);
        image_sizing[i].insert_or_assign("Project Name", project_name[i]);
    }

    std::string output;
    jsoncons::json_string_encoder encoder(output); 
    encoder.begin_object();
    encoder.key("Projects");
    encoder.begin_array();
    for (std::size_t i = 0; i < 5; ++i) 
    {
        image_sizing[i].dump(encoder);
    }
    encoder.end_array();
    encoder.end_object();
    encoder.flush();

    std::cout << output << "\n\n";
}

Or like this:

#include <jsoncons/json.hpp>

using jsoncons::json;

int main()
{
    json image_sizing(jsoncons::json_array_arg);
    image_sizing.resize(5);

    int project_no[5] = { 1, 2, 3, 4, 5 };
    std::string project_name[5] = {"XXX", "YYY", "ZZZ", "PPP", "RRR"};
    for (std::size_t i = 0; i < 5; ++i) 
    {
        image_sizing[i].insert_or_assign("Project Number", project_no[i]);
        image_sizing[i].insert_or_assign("Project Name", project_name[i]);
    }

    json projects;
    projects.try_emplace("Projects", std::move(image_sizing));

    std::cout << pretty_print(projects) << "\n\n";
}

The output is

{
    "Projects": [
        {
            "Project Name": "XXX",
            "Project Number": 1
        },
        {
            "Project Name": "YYY",
            "Project Number": 2
        },
        {
            "Project Name": "ZZZ",
            "Project Number": 3
        },
        {
            "Project Name": "PPP",
            "Project Number": 4
        },
        {
            "Project Name": "RRR",
            "Project Number": 5
        }
    ]
}

[Priyaankaa13]

Thanks alot, its working