c++ - Cant pass pipe's write-end as file desctiptor -

pipe's write-end file descriptor int functions such tcl_makefilechannel accepts void* file handle. need pass pipe write-end it. how can 1 convert 1 type of file handle another?

reading this reference seems pass file descriptor:

tcl_makefilechannel(reinterpret_cast<void*>(fd), ...); 

also might want read this thread.