Hi,
Extras.h is not include in the DSC libraries.
Attached to this post you will find a doc showing the MSL Compatibility.
Major functions of Extras.h are included in MACos and Windows only.
For Windows it's CodeWarrior for Windows desktop version not embedded.
The MSL_C_Reference.pdf manual is the same for all products (desktop and embedded)
In the description of the Itoa function there is the remark:
This function may not be implemented on all platforms.
Please have a look to the doc attached.
Regards
Pascal