Cast JSON value to certain types

[zliucd]

Hi,

Is is possible to cast a JSON value to certain types?

JSON example
{
  "name": "abc",
  "age": 15
}

void foo(string s)
{
   
}

json j;
foo(j["name"]);         

// Following code won't work with compiler errors
foo(dynamic_cast<string>(j["name"])) 
foo(reinterpret_cast<string> (j["name"])) 

An alternative will be ok, but it's more verbose

string tmp = j["name"];
foo(tmp)

Thanks.

[nlohmann]

See https://json.nlohmann.me/api/basic_json/get/

[PatchByte]

Your code should be like this:

// JSON example
// {
//   "name": "abc",
//   "age": 15
// };

void foo(string s)
{
   
}

// Ignore my spacing please, thx

json j;
if(j["name"].is_string() == true)
{
 foo( j["name"].get<std::string>() );
}

[nlohmann]

Rather use is_string()

[zliucd]

@nlohmann @PatchByte Thanks, it works well. But it does not work to pass params by reference, e.g.,

json j;
if(j["name"].is_string() == true)
{
    foo2( j["name"].get<std::string>() );
}

void foo2(string &s)
{
   
}

Compiler(Clang 13.0 in OSX M1) error message

candidate function not viable: expects an lvalue for 1st argument
void foo2(string &s);

There are alternatives I guess, like pass param inconst char *.

[nlohmann]

Use get_ref to get a reference to the string.

[FabianoGK]

Or declare `void foo2 (const string &s)`.

…

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