How to detect parse failure?

[davechurchill]

Apologies for the seemingly simple question, but there is no example for detecting a parse failure on the readme. Maybe one could be added, or a simple explanation of how to detect a parse failure could be given?

[davechurchill]

@nlohmann I see you saw this and added it to documentation, in the mean time while you work on it could you let me know how? I need it for a project :)

[nlohmann]

Parse errors are indicated by exceptions. In the 2.x.x series, the exception type is std::invalid_argument, in 3.x.x (develop branch), the exception type is json::parse_error. See https://github.com/nlohmann/json/blob/develop/doc/examples/parse_error.cpp for an example of the latter.

[davechurchill]

Thank you for the quick response. Might you consider adding a simple boolean to the json object indicating whether or not there was a parse error? Sometimes it is quite inconvenient to rely on exceptions for some things. Here's a sample use-case:

std::ifstream in(filename)
json j;
in >> j;

if (j.parseError()) { print error message }

[gregmarr]

What is inconvenient about this?

std::ifstream in(filename)
json j;

try {
    in >> j;
} catch(json::parse_error) {
    print error message;
}

[davechurchill]

Nothing is inconvenient about the code itself, apologies for implying that. It is inconvenient in the case where I am working with a codebase that has exceptions disabled :(

I completely understand if the feature request is not doable, just thought it wouldn't hurt to ask :)

[gregmarr]

Oh, that's a different case altogether. #582

std::ifstream in(filename)
json j = json::parse(in, nullptr, false);
if (j.is_discarded()) { print error message }

[davechurchill]

That's exactly what I'm looking for, thank you!

[naimac]

it'll be interesting for newbies like me, to remind that for parsing a jsonFile from the program's argument (linux) we have to do like so :

[linux] ./a.out "cat myFile.json"
[main.cpp] std::string myVar(argv[1])