Need a HELP on open NGC file

Hi everyone
Currently I'm testing some wood carving on LinuxCNC , the ngc file of wood carving is too big (10-20Mb) , when I opening the big ngc file , the GUI is stuck...(forgive my bad English)

So , I found the function "program_open" in /build/src/emc/usr_intf/axis/extensions/emcmodules.cc line 01062 (the version is 2.7.0) , but this function just cp the filename ,not cp the file(is right?).

Q1) where is the right function which implementation copying files from the hard disk into memory?(forgive my bad English again )
Q2) how can I solve this problem?
Thank !!!

Thank you andypugh , I know you mean and I will test it .

But I want to know the function where copying ngc files from the hard disk into memory in the source code? If you know that can you tell me? (I can't found this function On my own ability )

Thanks for replay