Format json code into std::string

Question

It's a beginner question, how would I format the following json array of strings into std::string

[
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },  
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },  
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  }
]

Here is the json string

const std::string json =
            "[\n"
            "  {\n"
            "    \"x\" : 0,\n"
            "    \"y\" : 0,\n"
            "    \"z\" : 0\n"
            "  },\n"
            "  {\n"
            "    \"x\" : 640,\n"
            "    \"y\" : 0,\n"
            "    \"z\" : 0\n"
            "  },\n"
            "  {\n"
            "    \"x\" : 640,\n"
            "    \"y\" : 0,\n"
            "    \"z\" : 480\n"
            "  },\n"
            "  {\n"
            "    \"x\" : 0,\n"
            "    \"y\" : 0,\n"
            "    \"z\" : 480\n"
            "  }\n"
            "]\n";


        Json::Value coordinates;
        Json::Reader reader;

        reader.parse( json, coordinates );

So I'm trying to parse the above json array, to get a list of coordinates, but it can't be parsed correctly.

Json is a string. It's not code. "[{"x:12.1},{"x":12.1"}]" is a Json string. What do you mean? Are you trying to create a — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Aug 30, 2017 at 8:58
Just like any other string. Json is a string, whose contents have a specific format. Nothing more. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Aug 30, 2017 at 9:00
what about the x, how would I make it work should I put +"\x"+ — andre
– andre, Commented Aug 30, 2017 at 9:00

Jarod42 · Accepted Answer · 2017-08-30 09:16:22Z

6

You might use raw string since C++11:

const std::string json = R"(
[
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },  
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  },  
  { 
    "x" : 12.1,
    "y" : 12.1,
    "z" : 12.1
  }
]
)";

before, you have to do some escaping as " -> \":

const std::string json = 
"[\n"
"  {\n"
"    \"x\" : 12.1,\n"
"    \"y\" : 12.1,\n"
"    \"z\" : 12.1\n"
"  },\n"
"  {\n"
"    \"x\" : 12.1,\n"
"    \"y\" : 12.1,\n"
"    \"z\" : 12.1\n"
"  },\n" 
"  {\n"
"    \"x\" : 12.1,\n"
"    \"y\" : 12.1,\n"
"    \"z\" : 12.1\n"
"  },\n"
"  {\n"
"    \"x\" : 12.1,\n"
"    \"y\" : 12.1,\n"
"    \"z\" : 12.1\n"
"  }\n"
"]\n";

edited Aug 30, 2017 at 9:16

answered Aug 30, 2017 at 9:02

Jarod42

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6 Comments

Andre Kampling Over a year ago

Also before he had to escape \n. For completeness: en.cppreference.com/w/cpp/language/string_literal see: prefix(optional) R "delimiter( raw_characters )delimiter" (6) (since C++11).

andre Over a year ago

Can you write it without the Raw, just for a complete answer

Panagiotis Kanavos Over a year ago

There is no need to use newlines. Whitespace is ignored in Json. Instead of " one can also use ' and avoid escaping altogether

Panagiotis Kanavos Over a year ago

@andre post actual code that reproduces your problem and include the full error message. It may be that you used invalid tags, or that a required tag is missing. Or it could be a quirk of the parser library. What is Json::Reader ?

Panagiotis Kanavos Over a year ago

@andre not yet. What is Json::Reader ? What is the error message? C++ doesn't have any Json support and the string is OK as it is.

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