how to compile project include libcurl "undefined reference"

Question

I'm using compile downloaded source code and try to make my c++ project but these error appear.

user1@ubuntu:~$ make
g++ -std=c++0x -g -Wall -Werror -L/home/user1/project0/libcurl/lib/libcurl.a -I/home/user1/proj/libcurl/include -c my-curl.cpp -o curl.o
g++ -std=c++0x -g -Wall -Werror -L/home/user1/project0/libcurl/lib/libcurl.a -I/home/user1/proj/libcurl/include -c main.cpp -o main.o
g++ -std=c++0x -g -Wall -Werror -L/home/user1/project0/libcurl/lib/libcurl.a -I/home/user1/proj/libcurl/include -o my-curl-app my-curl.o main.o 
my-curl.o: In function `CCurlDownloader::start_download()':
~/my-curl.cpp:22: undefined reference to `curl_easy_init'
~/my-curl.cpp:27: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:28: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:29: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:30: undefined reference to `curl_easy_perform'
~/my-curl.cpp:53: undefined reference to `curl_easy_cleanup'
collect2: ld returned 1 exit status
make: *** [my-curl-app] Error 1

and i'm changed -L option to specified directory and add -lcurl for specified lib and result is.

user1@ubuntu:~/project0/my-curl$ make
g++ -std=c++0x -g -Wall -Werror -L/home/user1/practics/libcurl/lib -lcurl -I/home/user1/practics/libcurl/include  -c my-curl.cpp -o my-curl.o
g++ -std=c++0x -g -Wall -Werror -L/home/user1/practics/libcurl/lib -lcurl -I/home/user1/practics/libcurl/include  -c main.cpp -o main.o
g++ -std=c++0x -g -Wall -Werror -L/home/user1/practics/libcurl/lib -lcurl -I/home/user1/practics/libcurl/include  -o my-curl-cpp my-curl.o main.o 
my-curl.o: In function `CCurlDownloader::start_download()':
~/my-curl.cpp:22: undefined reference to `curl_easy_init'
~/my-curl.cpp:27: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:28: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:29: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:30: undefined reference to `curl_easy_perform'
~/my-curl.cpp:53: undefined reference to `curl_easy_cleanup'
collect2: ld returned 1 exit status
make: *** [bb-cppurl] Error 1

I and try curl-config to link libs but result still be the same.

user1@atom-linux-server:~/my-curl$ make
g++ -std=c++0x -g -Wall -Werror `/home/user1/project0/libcurl/bin/curl-config --libs` `/home/user1/project0/libcurl/bin/curl-config --cflags`  -c my-curl.cpp -o my-curl.o
g++ -std=c++0x -g -Wall -Werror `/home/user1/project0/libcurl/bin/curl-config --libs` `/home/user1/project0/libcurl/bin/curl-config --cflags`  -c main.cpp -o main.o
g++ -std=c++0x -g -Wall -Werror `/home/user1/project0/libcurl/bin/curl-config --libs` `/home/user1/project0/libcurl/bin/curl-config --cflags`  -o my-curl-app my-curl.o main.o 
my-curl.o: In function `CCurlDownloader::start_download()':
~/my-curl.cpp:22: undefined reference to `curl_easy_init'
~/my-curl.cpp:27: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:28: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:29: undefined reference to `curl_easy_setopt'
~/my-curl.cpp:30: undefined reference to `curl_easy_perform'
~/my-curl.cpp:53: undefined reference to `curl_easy_cleanup'
collect2: ld returned 1 exit status
make: *** [bb-cppurl] Error 1

Answer 1

I move

-L/home/user1/practics/libcurl/lib -lcurl

to the tail of command

g++ -std=c++0x -g -Wall -Werror -I/home/user1/practics/libcurl/include -o my-curl-cpp my-curl.o main.o -L/home/user1/practics/libcurl/lib -lcurl

and it works.

Answer 2

You're using the build tools wrong.

1 - the -L option should specify a directory

2 - there's no -l (lowercase L) option to specify which lib to link with (perhaps from the directory -L identifies)