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trof asked
Medium Priority
Last Modified: 2013-12-26
I wrote small CGI (C language), and it using sockets. Source code compiles without any problem, but during linking I've got messages

Undefined                       first referenced
 symbol                             in file
socket                              /var/tmp/cca000Ms1.o
inet_addr                           /var/tmp/cca000Ms1.o
sendto                              /var/tmp/cca000Ms1.o
shutdown                            /var/tmp/cca000Ms1.o  

So, I guess, GCC does not see some libraries
Does enybody know, which flags should I use, to include this library into linking process ?
Thanks in advance
Alexey Trofimov
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Most Valuable Expert 2014
Top Expert 2015

cc -lsocket
Which OS do you have?
For most UNIXs they should be in  libc.a and/or libc.so.


SunOS 5.5.1
Actually, GCC -lsocket works for all entries, except "inet_addr"...


oooppss, sorry, maybe, it's another error...

Undefined                       first referenced
 symbol                             in file
inet_addr                           /var/tmp/cca0006H1.o  (symbol belongs to imp
licit dependency /usr/lib/libnsl.so.1)
So, what I suppose to do now ?
try to find the library which contains the requested symbol, add this library to your link command.

#! /bin/csh -f -b
foreach l (/usr/lib/lib*.so.*)
echo ------------- $l
nm -gop $l | grep inet_addr


Thanks, I guess, how it suppose to work, but

------------- /usr/lib/libC.so.3
nm: Command not found

Ok, let's say, I found 5-10 files, include "inet_addr". Some of them just call this function, right ? How I know witch one does contain real code of this function(not just call of it ) ? And if I know exactly name of proper file, what should I type in command line of GCC ?
no nm? Sounds strange. Do you need a path to it?

Anyway, nm reports the referenced and defined symbols in a library. Defined (text) symbols are marked  T  or  t, undefined (referenced) symbols are marked  U. This is how you can find the right library.

Of cause my shell example could be more sophisticated to get only the desired names, but this also should report what you need.

If you have no  nm,  strings  (without options) could be used, but it does not give you a hint if its defined or referenced.

Should I've marked it as answer ;-)

I'm astonished ... the entire socket stuff is supposed to
be part of libc.a. Are you sure you're linking in the
correct libc.a, i.e. /usr/lib/libc.a (or equivalent).

Could you show the actual command line you're using for
the linkage of this all?

kind regards,

Jos aka jos@and.nl

Actually, you need

-lsocket -lnsl

on your link line.  That's the SVR4 approach :)


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Unfortunately I'm off from Solaris (SunOS 5.x), that's why I suggested to search for the symbols in the existing libs.

As far as I could remember  -lnsl  is the the approach, thanks rembo. As closer as one get to SVR4  -lsocket  is it too :)
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