martinwork
commented
8 months ago @JohnVidler @finneyj
The ticket is about using MakeCode serial.writeString etc. to send a string containing a zero, created with text from char code(0), to communicate with a device.
There is a block for serial.writeBuffer, but creating the buffer in Javascript mode and filling the buffer is just less convenient. Of course, the mess can be hidden in a function, custom.ts or extension, but...
It still feels like a bug that the string created in MakeCode becomes empty. As far as I can see from the GitHub history this hasn't changed since the earliest DAL. I suppose if strings can contain zero, everything that accepts a string must deal with zero!
Arising from support ticket https://support.microbit.org/helpdesk/tickets/67883 (private)
A MakeCode string containing a zero character becomes empty when it's converted to a DAL/CODAL ManagedString.
This project displays the string in the MakeCode simulator, but not in micro:bit. https://makecode.microbit.org/_bT89KTV9U2wA The support ticket is about putting 0 in a string to send to serial.
The ManagedString constructor used in the conversion empties strings that contain a zero character. https://github.com/microsoft/pxt-common-packages/blob/master/libs/core/pxt.h#L26 https://github.com/lancaster-university/codal-core/blob/master/source/types/ManagedString.cpp#L244 https://github.com/lancaster-university/microbit-dal/blob/master/source/types/ManagedString.cpp#L252
The constructor from a ManagedBuffer doesn't filter zeros. https://github.com/lancaster-university/codal-core/blob/master/source/types/ManagedString.cpp#L221
initString says "We assume the string is... null terminated", but doesn't really assume that. https://github.com/lancaster-university/codal-core/blob/master/source/types/ManagedString.cpp#L77