JSONify string in C++

Question

In my program I need to output simle JSON data. I looked at many libraries for JSON in c++, they are too complex for my task. Is there some easier way, how to create JSON-safe string from any c++ string?

string s = "some potentially dangerous string";
cout << "{\"output\":\"" << convert_string(s) << "\"}";

How would function convert_string(string s) look like?

thanks

You'll probably want to take a look at the JSON format on: json.org — Kevin
– Kevin, Commented Feb 22, 2011 at 13:19

etarion · Accepted Answer · 2011-02-22 14:27:36Z

4

If your data is in UTF-8, per the string graph on http://json.org/:

#include <sstream>
#include <string>
#include <iomanip>
std::string convert_string(std::string s) {
    std::stringstream ss;
    for (size_t i = 0; i < s.length(); ++i) {
        if (unsigned(s[i]) < '\x20' || s[i] == '\\' || s[i] == '"') {
            ss << "\\u" << std::setfill('0') << std::setw(4) << std::hex << unsigned(s[i]);
        } else {
            ss << s[i];
        }
    } 
    return ss.str();
}

edited Feb 22, 2011 at 14:27

answered Feb 22, 2011 at 13:28

etarion

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5 Comments

Fred Nurk Over a year ago

Doesn't handle control characters, which must be escaped with \uHHHH notation.

Ondra Over a year ago

thanks, but is there some simple way, how to escape these characters?

etarion Over a year ago

@Fred: D'oh, i missed the "control character" part in the header, my bad.

etarion Over a year ago

@Ondra: fixed so it produces escaped versions of control characters too (for simplicity, also produces \uXXXX for \ and ").

Fred Nurk Over a year ago

When char is signed, many more chars will be less than 0x20 than you want to include. And I've never liked that + obfuscation. Why not int(s[i])?

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