My code below crashes(Debug Error! R6010 abort() has been called). Can you help me? I'd also would like to know how to initialize the json object from a string value.
Json::Value obj;
obj["test"] = 5;
obj["testsd"] = 655;
string c = obj.asString();
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3 Answers
Hello it is pretty simple:
1 - You need a CPP JSON value object (Json::Value) to store your data
2 - Use a Json Reader (Json::Reader) to read a JSON String and parse into a JSON Object
3 - Do your Stuff :)
Here is a simple code to make those steps:
#include <stdio.h>
#include <jsoncpp/json/json.h>
#include <jsoncpp/json/reader.h>
#include <jsoncpp/json/writer.h>
#include <jsoncpp/json/value.h>
#include <string>
int main( int argc, const char* argv[] )
{
std::string strJson = "{\"mykey\" : \"myvalue\"}"; // need escape the quotes
Json::Value root;
Json::Reader reader;
bool parsingSuccessful = reader.parse( strJson.c_str(), root ); //parse process
if ( !parsingSuccessful )
{
std::cout << "Failed to parse"
<< reader.getFormattedErrorMessages();
return 0;
}
std::cout << root.get("mykey", "A Default Value if not exists" ).asString() << std::endl;
return 0;
}
To compile: g++ YourMainFile.cpp -o main -l jsoncpp
I hope it helps ;)
4 Comments
Rahim Khoja
Wow, this has been the best quick primer on C++ and json I have seen. awesome
Jarod42
With raw string (C++11), you may use
strJson = R"({"mykey" : "myvalue"})";.
jungletek
FWIW, you should only need to include the single
json.h header.
Technophile
Json::Reader is deprecated. Use CharReader and CharReaderBuilder instead.
Json::Reader is deprecated. Use Json::CharReader and Json::CharReaderBuilder instead:
std::string strJson = R"({"foo": "bar"})";
Json::CharReaderBuilder builder;
Json::CharReader* reader = builder.newCharReader();
Json::Value json;
std::string errors;
bool parsingSuccessful = reader->parse(
strJson.c_str(),
strJson.c_str() + strJson.size(),
&json,
&errors
);
delete reader;
if (!parsingSuccessful) {
std::cout << "Failed to parse the JSON, errors:" << std::endl;
std::cout << errors << std::endl;
return;
}
std::cout << json.get("foo", "default value").asString() << std::endl;
Kudos to p-a-o-l-o for their answer here: Parsing JSON string with jsoncpp
2 Comments
BoeroBoy
Thanks for this update. It never ceases to amaze me how simple code gets deprecated and replaced by 3x complexity.. Cheers.
Technophile
Documentation link is broken; now at: open-source-parsers.github.io/jsoncpp-docs/doxygen/index.html
You can avoid using Json::CharReader and Json::CharReaderBuilder by using stringstream instead.
#include <string>
#include <sstream>
#include "jsoncpp/json/json.h"
int main() {
std::string strJson = "{\"mykey\" : \"myvalue\"}";
Json::Value obj;
// read a JSON String
stringstream(strJson) >> obj;
// get string value
std::string value1 = obj["mykey"].asString();
// or to get a default value if it isn't set
std::string value2 = obj.get("mykey", "...").asString();
return 0;
}
