For example:

qDebug() << QJsonDocument::fromJson( "\{\"key\": 0E-1}" ).object();
qDebug() << QJsonDocument::fromJson( "\{\"key\": 0e-1}" ).object();
qDebug() << QJsonDocument::fromJson( "\{\"key\": 1E-1}" ).object();
qDebug() << QJsonDocument::fromJson( "\{\"key\": 1e-1}" ).object();

Output:

QJsonObject()
QJsonObject(\{"key":0})
QJsonObject(\{"key":0.1})
QJsonObject(\{"key":0.1})

The first example, QJsonDocument after parse can not output the correct results. QJsonDocument is null.

From Qt document (JSON Support in Qt)
Qt is to support RFC-4627, and RFC-4627 has said:

An exponent part begins with the letter E in upper or lowercase, which may be followed by a plus or minus sign. The E and optional sign are followed by one or more digits.

I also tried some JSON parsing tools, they can be normal analysis: {"key": 0E-1}

Such as this tool:

http://tool.oschina.net/codeformat/json