How do I link libcurl to my c++ program in linux?

Question

I need to use libcurl in a piece of software I am writing on my ubuntu machine. I am using Eclipse to write and compile all of the software. When I put the libcurl files in the same folder as the.cpp file, and include the curl.h file in the header, When I attempt to compile the program, It comes up with these errors:

Building target: sms
Invoking: GCC C++ Linker
g++  -o"sms"  ./src/sms.o   
./src/sms.o: In function `main':
/home/geekman/workspace/sms/Debug/../src/sms.cpp:38: undefined reference to `curl_easy_init'
/home/geekman/workspace/sms/Debug/../src/sms.cpp:42: undefined reference to `curl_easy_setopt'
/home/geekman/workspace/sms/Debug/../src/sms.cpp:44: undefined reference to `curl_easy_setopt'
/home/geekman/workspace/sms/Debug/../src/sms.cpp:46: undefined reference to `curl_easy_perform'
/home/geekman/workspace/sms/Debug/../src/sms.cpp:47: undefined reference to `curl_easy_cleanup'
collect2: ld returned 1 exit status
make: *** [sms] Error 1

I took the contents of the include folder from libcurl, and placed them in the same folder as the.cpp file. then in the header of the.cpp file, I typed:

#include <curl/curl.h>

I also tried:

#include "curl/curl.h"

Any ideas on the problem? Thanks.

Answer 1

Your header file inclusions are just fine; your problem is occurring at the linking step. In order to link against libcurl, you need to add the -lcurl command line option, assuming it's installed in a standard directory:

g++ -o sms ./src/sms.o -lcurl

If it's not installed in a standard directory, you also need to add the -L/path/to/libcurl , eg something like:

# Assuming that /home/geekman/workspace/libcurl is where libcurl.a is located
g++ -o sms ./src/sms.o -L/home/geekman/workspace/libcurl -lcurl

Also note that the -lcurl option has to appear after the list of object files you're linking, otherwise it won't link properly.

Answer 2

You can try to use curl-config --libs .

Answer 3

An alternate answer (the first one is excellent). Consider using the output returned by "pkg-config --libs libcurl" as an argument to your compiler.

For example,

CPPFLAGS=`pkg-config --libs libcurl`

g++ $CPPFLAGS myfile.o

Pkg-config is a standard way for open source libraries to communicate to you how to link against them / #include their files.

Answer 4

Anyone who is using ecplise CDT then you need to do following. First on terminal enter

curl-config --libs

On my machine, the result is

-L/usr/lib/i386-linux-gnu -lcurl

then do according to this screenshot and you will be able to compile. btw don't forget to add header files in your code

So you enter library folder path without -L and library name without -l because they will be automatically added by linker.

Answer 5

You have to link the library to your program. With gcc (and most other compilers) you can specify the libraries to link with -lname_wo_lib , eg -lcurl

Answer 6

Also see GNU GCC Manual - Options for Linking for a detailed explanation of the options Adam Rosenfield said. For standard search directories, see An Introduction to GCC - for the GNU Compilers gcc and g++ - Setting Search Paths .

Answer 7

In addition to the first answer, I had to link the curlpp library too. So to compile the main.cpp file which included the curlpp I had to do:

g++ main.cpp -lcurl -lcurlpp

Using only one of the two links would return different errors regarding different links. It is important to remind that this only worked because I had installed all the necessary libraries in the standard include folders