Writing lines of file into JSON using C++ and jsoncpp

Question

I have a text file that I'm trying to convert to a JSON object using jsoncpp in my c++ application.

The contents of the file is formatted as so:

system type : Atheros AR7241 rev 1
machine     : Ubiquiti UniFi
processor   : 0
cpu model   : MIPS 24Kc V7.4
BogoMIPS    : 259.27

Which seems pretty handy to start. I needed to keys to match the first column and the values the second column, as so:

{ "meh" : [{ "system type" : "Atheros AR7241 rev 1", "machine" : "Ubiquiti UniFi" ...

I can write the file in it's entriety to a json object. But that's as far as I can get...

Json::Value root;
string line;

ifstream myfile( "/proc/cpuinfo" );
if (myfile)
{
    while (getline( myfile, line ))
    {
        root["test"] = line;
        cout << root;
    }
    myfile.close();
}

Which is close but obviously gives me json like so:

{
    "test" : "system type   : Atheros AR7241 rev 1"
}

Am new to c++ I don't know how to split the lines at the colon and use the first half for the key instead of "test".. Can someone suggest a way to go about this?

Answer 1

I would suggest using a combination of "string::find()" and "string::substr()".

Or some regular expression stuff but i think that would need to go over the standard library.

Example:

std::string::size_type n;
std::string key;
std::string value;

n = line.find(':');

key = line.substr( 0, n );
value = line.substr( n+1 );

Then would need maybe to strip the key and values from white characters. I won't cover it since there are few question and answers on SO how to do it. E.g:

1. Similar function in C++ to Python's strip()?
2. What's the best way to trim std::string?

EDIT:

Complete example code split.cpp:

/// TRIMMING STUFF
// taken from https://stackoverflow.com/a/217605/1133179
#include <algorithm> 
#include <functional> 
#include <cctype>
#include <locale>

// trim from start
static inline std::string &ltrim(std::string &s) {
        s.erase(s.begin(), std::find_if(s.begin(), s.end(), std::not1(std::ptr_fun<int, int>(std::isspace))));
        return s;
}

// trim from end
static inline std::string &rtrim(std::string &s) {
        s.erase(std::find_if(s.rbegin(), s.rend(), std::not1(std::ptr_fun<int, int>(std::isspace))).base(), s.end());
        return s;
}

// trim from both ends
static inline std::string &trim(std::string &s) { return ltrim(rtrim(s)); }
/// ~~~ TRIMMING STUFF ~~~


#include <string>
#include <iostream>

int main(){
std::string::size_type n;
std::string key;
std::string value;

std::string line = "system type : Atheros AR7241 rev 1";

n = line.find(':');

key = line.substr( 0, n );
value = line.substr( n+1 );
std::cout << "line: `" << line << "`.\n";
std::cout << "key: `" << key << "`.\n";
std::cout << "value: `" << value << "`.\n";


///  With trimming

std::cout << "{\n "json" : [{ \"" << trim(key) << "\" : \"" << trim(value) << "\" }]\n}\n";
}

Execute:

luk32:~/projects/tests$ g++ ./split.cpp
luk32:~/projects/tests$ ./a.out 
line: `system type : Atheros AR7241 rev 1`.
key: `system type `.
value: ` Atheros AR7241 rev 1`.
{
 "json" : [{ "system type" : "Atheros AR7241 rev 1" }]
}

I think it's ok.