questions with g++ linker

andrewscs · 07-20-2010, 04:24 AM

i've compiled libpdfdoc and placed the static library libpdfdoc-static.a in /usr/lib64/

i've written a small program(test.cpp) to test the library

Code:

#include <iostream>
#include "libpdfdoc.hh"

int main()
{
        pdf::Doc *doc = pdf::CreateDoc();
        std::cout << "Hello" << std::endl;
        return 0;
}

then i run the following and get the output :

Code:

$ g++ -I/home/usr/libpdf/include -c test.cpp
$ g++ -L/usr/lib64 -lpdfdoc_static test.o -o test
test.o: In function `main':
test.cpp:(.text+0x9): undefined reference to `pdf::CreateDoc()'
collect2: ld returned 1 exit status

can anyone tell me what is wrong? i even try placing the full path to the library(g++ /usr/lib64/libpdfdoc_static.a test.o -o test) but the same error shown..

i'm using Fedora 13 64bits..

JohnGraham · 07-20-2010, 05:04 AM

Quote:

Originally Posted by andrewscs

Code:

$ g++ -I/home/usr/libpdf/include -c test.cpp
$ g++ -L/usr/lib64 -lpdfdoc_static test.o -o test
test.o: In function `main':
test.cpp:(.text+0x9): undefined reference to `pdf::CreateDoc()'
collect2: ld returned 1 exit status

can anyone tell me what is wrong? i even try placing the full path to the library(g++ /usr/lib64/libpdfdoc_static.a test.o -o test) but the same error shown..

Your problem is not where the library is - if the linker couldn't find it, you'd get something like "cannot find -lpdfdoc_static".

Your problem is most likely one of ordering. Try moving the -l... directive after test.o, like so:

Code:

$ g++ -L/usr/lib64 test.o -o test -lpdfdoc_static

johnsfine · 07-20-2010, 05:58 AM

Quote:

Originally Posted by JohnGraham

Try moving the -l... directive after test.o

I agree. In general the -l's must appear later on the command line than the inputs that depend on those -l's. test.o depends on -lpdfdoc_static, so -lpdfdoc_static must come later on the command line than test.o.

andrewscs · 07-20-2010, 07:39 AM

it works... thank you so much..
by the way, where do you recommend i study more on the g++ ??
i'm new to g++...

andrewscs · 07-20-2010, 08:06 AM

if i have a directory '/home/user/myLib' and '/home/user/myInclude'
how do i include both of these directories into the default search path and default include path of g++?

bigearsbilly · 07-21-2010, 04:30 AM

are you using gnu make? (you don't need a makefile)
if not you should.

try this:

Code:

export LDFLAGS="-L /home/user/myLib"
export CXXFLAGS="-I /home/user/myInclude"
export LDLIBS="-lfdoc-static"
make test

note:
CXXFLAGS for C++
CFLAGS for C

it's probably not necessary to put your libs in the system lib
directory.
I wouldn't anyway.