How to access the first element of an Json::Value array

To access the first element of an Json::Value array the following code may not work:

...
double x = point[0].asDouble()
...

Instead you have to write:

...
double x = point[0u].asDouble()
...

To find out why just check the following fragment of the Json::Value documentation:

const Value & operator[] (int index) const
Access an array element (zero based index)
You may need to say 'value[0u]' to get your compiler to distinguish this from the operator[] which takes a string.