As written, the code is certainly an invitation for a memory leak. That alone would be enough for me to question the quality of the entire library code and motivate me to rewrite it myself.
There are several ways to improve it ... for example use STL smart pointers or containers. But, the simplest would probably be for the calling function to provide the storage space (as an array) and pass a pointer to it into the conversion function (along with a maximum size). The conversion function would then fill the storage provided by the caller.