[Xapian-discuss] undefined reference to "function name"

[Zhiguo Li]

Hi,

I am trying to add some functions to the Xapian library but when I tried 
to compile it, the linker give me the "undefined reference" error.

Here is what  I did:

Under directory matcher, I created two files "something.cc" and 
"something.h".

File "something.h":

#include "xapian/enquire.h"
#include "xapian/query.h"
#include "database.h"
void something();

File "something.cc":
#include "something.h"
void something() {};

And in examples/simplesearch.cc, I included "something.h" and called 
something() in the main function.

In the Makefile.mk under matcher directory, I added matcher/something.h 
in section "noinst_HEARDERS" and matcher/something.cc in section 
"libxapian_la_SOURCES".

Then I tried to compile the project, and from the compiler output it 
looks "something.cc" was compiled fine:

    /bin/bash ./libtool  --tag=CXX   --mode=compile g++ -DHAVE_CONFIG_H 
-I. -I./common -I./include     -Wall -W -Wredundant-decls 
-Wpointer-arith -Wcast-qual -Wcast-align -Wno-long-long 
-Wformat-security -Wconversion -fno-gnu-keywords -Wundef -Wshadow 
-Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2 -MT 
matcher/something.lo -MD -MP -MF $depbase.Tpo -c -o matcher/something.lo 
matcher/something.cc &&\
    mv -f $depbase.Tpo $depbase.Plo
 g++ -DHAVE_CONFIG_H -I. -I./common -I./include -Wall -W 
-Wredundant-decls -Wpointer-arith -Wcast-qual -Wcast-align 
-Wno-long-long -Wformat-security -Wconversion -fno-gnu-keywords -Wundef 
-Wshadow -Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2 -MT 
matcher/something.lo -MD -MP -MF matcher/.deps/something.Tpo -c 
matcher/something.cc  -fPIC -DPIC -o matcher/.libs/something.o
 g++ -DHAVE_CONFIG_H -I. -I./common -I./include -Wall -W 
-Wredundant-decls -Wpointer-arith -Wcast-qual -Wcast-align 
-Wno-long-long -Wformat-security -Wconversion -fno-gnu-keywords -Wundef 
-Wshadow -Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2 -MT 
matcher/something.lo -MD -MP -MF matcher/.deps/something.Tpo -c 
matcher/something.cc -o matcher/something.o >/dev/null 2>&1


But when "examples/simplesearch.cc" was compiled, it gave the following 
error:

depbase=`echo examples/simplesearch.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\
    g++ -DHAVE_CONFIG_H -I. -I./common -I./include     -Wall -W 
-Wredundant-decls -Wpointer-arith -Wcast-qual -Wcast-align 
-Wno-long-long -Wformat-security -Wconversion -fno-gnu-keywords -Wundef 
-Wshadow -Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2 -MT 
examples/simplesearch.o -MD -MP -MF $depbase.Tpo -c -o 
examples/simplesearch.o examples/simplesearch.cc &&\
    mv -f $depbase.Tpo $depbase.Po
/bin/bash ./libtool  --tag=CXX   --mode=link g++ -Wall -W 
-Wredundant-decls -Wpointer-arith -Wcast-qual -Wcast-align 
-Wno-long-long -Wformat-security -Wconversion -fno-gnu-keywords -Wundef 
-Wshadow -Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2   -o 
examples/simplesearch examples/simplesearch.o  libxapian.la
g++ -Wall -W -Wredundant-decls -Wpointer-arith -Wcast-qual -Wcast-align 
-Wno-long-long -Wformat-security -Wconversion -fno-gnu-keywords -Wundef 
-Wshadow -Winit-self -Wstrict-overflow=5 -fvisibility=hidden -g -O2 -o 
examples/.libs/simplesearch examples/simplesearch.o  
./.libs/libxapian.so -lz
examples/simplesearch.o: In function `main':
/home/zhiguoli/xapian/examples/simplesearch.cc:83: undefined reference 
to `something()'
collect2: ld returned 1 exit status
make[2]: *** [examples/simplesearch] Error 1


My question is why the linker couldn't find the definition of function 
"something()"? How to make it work? I am not clear about the overall 
design structure of Xapian yet, but I would like to make some quick hack 
and very small changes (for example, add a few functions to libxapian).

Thanks,
Kevin