Thread: JSON Advise for C++

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Code:

std::string person = "{name:\"Melinda\", surname:\"Rose\", address:\"New York\"}";

Parsing that without a library should not be difficult, but if you are going to have to parse more complex JSON representations, then you might as well use a well-tested library instead of implementing your own parser.

Originally Posted by JessicaS

Just checked above mentioned library and it compiled 4MB just for lib_json.lib. My original program is 300KB. Am I done something wrong or is this kind of libraries are normally big?

Could be a matter of static linking versus dynamic linking, or maybe the library has a large dependency or pulls in more dependencies than necessary.

I did a quick check, and actually that is invalid JSON. The JSON representation should have been:

Code:

{"name":"Melinda", "surname":"Rose", "address":"New York"}

Originally Posted by JessicaS

could you please guide me how can I parse my JSON string by myself?

Well, a simple approach is to do three passes: on each pass, you search for the key ("name", "surname", or "address") such that it is followed by a ":" possibly with whitespace in between. If you fail to find a key followed by a colon, then you know the input is invalid. Otherwise, you then find the first '"' after the colon, upon which you know the value starts. Then you search for another '"' that is not preceded by a backslash, upon which you have obtained the entire string value. If you fail to find such a '"', then the input is invalid. If you do find it, perhaps you could do a bit more validation by checking that the next non-whitespace character is a comma or a closing brace. This approach would allow for plenty of illegal JSON to pass muster, but that might not matter.

Use Cereal. You will not regret it.

Originally Posted by JessicaS

It will be simple I suppose. I dont think I will need very much nested JSON strings. Just concerned about some localization like Arabic or Chinese characters or empty spaces.

The easiest way to deal with localization is to use UTF8 encoding in your files. They can be read and manipulated with simple std::strings which exists in the standard library (Cereal can handle UTF8 perfectly fine). If you're going to output it somewhere in Windows (e.g. message box), then make sure to convert it to UTF16LE before (see your other thread).