I compiled an .cc file with the following command, which is in Makefile code:
bin/bash ../libtool --silent --tag=CXX --mode=compile g++ -DHAVE_CONFIG_H -I.
-I.. -I../include/ -I.. -g -O2 -MT rtpsession_inet.lo -MD -MP -MF
.deps/rtpsession_inet.Tpo -c -o rtpsession_inet.lo rtpsession_inet.cc
There is a function named rtp_session_rtp_recv in the .cc file. However, it is said that the reference of this function cannot be found when I use the library generated by the Makefile.
So I checked the .o file generated by rtpsession_inet.cc and find that there is not a function named rtp_session_rtp_recv while the function name is changed to _Z20rtp_session_rtp_recvP11_RtpSessionj.
Meanwhile, there are several other functions changes their name, e.g. rtp_session_rtp_send -> _Z20rtp_session_rtp_sendP11_RtpSessionP4msgb.
But functions such as rtp_session_set_remote_addr_full are not changed at all.
What is the additional characters' meaning? How can I deal with this problem?
I compile the file in Linux and use command
nm rtpsession_inet.o
to read the .o file. (All the functions including the one with incorrect name are with T tag, which means the reference exists)
Thanks!
This is called name mangling.
It's for the benefit of the linker. A C++ compiler is able to resolve multiple functions of the same name, based on their argument types. For example, you might have a function called print that takes an int argument, and another that takes a char* argument. The compiler knows which one to generate a call to based on what type of argument you pass to it.
Calls across translation units, though, have to be resolved by the linker, which typically is not aware of C++ overloading rules and has to resolve calls based only on the name. So the C++ compiler decorates the name with enough information to resolve the overload.
The C++ standard doesn't specify how this is done, but if you look at the name you can probably work out how the mangled name is generated.
How can I deal with this problem?
The compiler and linker should resolve calls correctly. What problem are you referring to?
The additional characters are symbol "decorations" added by the compiler and are used to identify the function/method signature, i.e. the return type and the parameters. It helps the runtime determine which one of many functions of the same name (overloading) to invoke in any given invocation.
