Problem with static library linking

Problem with static library linking

[Harish]

Hi,

I am having a problem with the static library as explained below.


There was an existing static library libpcap.a 
I created a new static library with the name mylib.a , mylib.a calls a function func() in libpcap.a.

I created mylib.a using the below command

ar rcs mylib.a *.o libpcap.a
ranlib mylib.a

mylib.a has been successfully made. 

But when I use mylib.a with an executable it says undefined symbol for the function func() in the file which is present in mylib.a.

I used the command "nm mylib.a | grep func" to verify that mylib.a actually contains func().

But still I am getting linking error.

In my link line  libpcap.a comes before mylib.a

Could you please help.

I would be very thankful.

-Harish

Re: Problem with static library linking

[Eljay Love-Jensen]

Hi Harish,

> In my link line libpcap.a comes before mylib.a

Since mylib.a depends on libpcap.a, mylib.a should come before libpcap.a on
your link line.

Otherwise, unfulfilled symbols in mylib.a won't be found because libpcap.a
had already been processed.

Order of archives on the link line is significant.

If you have circular dependencies in your archive libraries (ugh! Avoid if
possible!), you can do:

gcc -o myapp \
 foo.c \
 alpha.a \
 beta.a \
 alpha.a

...or on many platforms that use GNU ld...:

gcc -o myapp \
 foo.c \
 --Wl,--whole-archive \
   alpha.a beta.a \
 --Wl,--no-whole-archive

HTH,
--Eljay