Problem in dump() in json.h caused by ss.imbue

[cvengelen]

We have been using json.h for Json input and output in our product without problems.

However, until now I have build a Debug version of the product, and now I started building for a Release configuration. I immediately got a Heap exception in the last statement of the dump() method of json. This must have been a problem in some destructor, so just to be sure I changed the dump code in the following way:

string_t dump(const int indent = -1) const
{
string_t tmp;
{
    std::stringstream ss;
    // fix locale problems
    ss.imbue(std::locale(std::locale(), new DecimalSeparator));

    if (indent >= 0)
    {
        dump(ss, true, static_cast<unsigned int>(indent));
    }
    else
    {
        dump(ss, false, 0);
    }

    // CvE Test heap problem for Release configuration
    tmp = ss.str();
}
    return tmp;
}

The Heap exception then occurs when the block statement with the ss declaration is left, so caused by the ss destructor. Also see attached VS2015 screenshot.

Just as a guess, I then commented out the ss.imbue call, and then the Heap exception disappeared immediately.

Again, note that this problem only occurs when compiling for the Release configuration (with /MT in VS2015 instead of /MTd).

[nlohmann]

Hey @cvengelen, thanks for reporting. This looks really strange, because we are running the AppVeyor tests (see https://github.com/nlohmann/json/blob/develop/appveyor.yml) in Release mode.

[nlohmann]

Maybe someone with more insights to MSVC can help.

[TurpentineDistillery]

This is possibly #359.
Please try a newer version of the library.

[nlohmann]

@cvengelen Which version of the library are you using?

[cvengelen]

The project is using version 2.0.1. Note that there are no statics inthe call to ss.imbue:

	std::stringstream ss;
	// fix locale problems
	ss.imbue(std::locale(std::locale(), new DecimalSeparator));

I'll check with the latest json version.,

[cvengelen]

This issue is resolved in version 2.1.0 (or in another version between 2.0.1 and 2.1.0).
In version 2.1.0, the call to ss.imbue is replaced by two separate calls:

    // fix locale problems
    ss.imbue(std::locale::classic());

    // 6, 15 or 16 digits of precision allows round-trip IEEE 754
    // string->float->string, string->double->string or string->long
    // double->string; to be safe, we read this value from
    // std::numeric_limits<number_float_t>::digits10
    ss.precision(std::numeric_limits<double>::digits10);

Somehow this solves my original problem: the heap exception does not occur anymore.
Thanks for the support!
Chris.

[nlohmann]

Thanks for the feedback!