A trivial IDAPy script to dump and demangle all C++ functions

idapy-cpp-demangle.py

import idautils

for mangled in idautils.Functions():
    demangled = idc.Demangle(
        str(idaapi.get_func_name(mangled)),
        idc.GetLongPrm(idc.INF_SHORT_DN)
    )
  
    if demangled is not None:
        print "{} => {}".format(mangled, demangled)

< yrp> fyi your code depends on IDA being aware of all function boundaries
< yrp> theres not a better way to do it
< yrp> just headsup that you might need to rerun it if you identify more functions

good. how to propagate these symbols in IDA?

import idautils

for mangled in idautils.Functions():
    demangled = idc.demangle_name(idaapi.get_func_name(mangled), idc.INF_SHORT_DN)
  
    if demangled is not None:
        print("{} => {}".format(mangled, demangled))

Updated for IDA 7+ and Python 3+