如何编译项目包括 libcurl “未定义的引用”

Question

我正在使用编译下载的源代码并尝试制作我的 c++ 项目，但出现这些错误。

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

我将 -L 选项更改为指定目录，并为指定的库添加 -lcurl，结果是。

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

我并尝试 curl-config 链接库，但结果仍然相同。

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

你使用错误的构建工具。

1 - -L 选项应该指定一个目录

2 - 没有 -l（小写 L）选项来指定要链接的库（可能来自 -L 标识的目录）

Answer 2

我移动

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

到命令的结尾

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

它有效。