g++ can't link curl lib files

Question

I'm having some issues with getting g++ to link the curl lib files. I'm using Visual Studio 2017 with the linux dev plugin and Ubuntu Server 17.04.

curl-config --libs gave an output of -Lcurl which I tried adding to the linker options in Project settings > Linker > Command Line > Additional options. I also added the --cflags output to the compile options. This didn't fix the issue.

Then I tried the source from the website and used make and make install. curl-config --libs gave me a different output of -L/usr/local/lib -lcurl. I changed the options in the linker and this still didn't work.

The linker output says lots of "undefined reference to " and then the curl methods. I have #include <curl/curl.h> in the cpp file.

Any ideas?
Thanks

Answer 1

With a default installion you will specify the curl library to gcc with -lcurl, as reported by curl-config --libs. And to pass this on the gcc command line generated by VCLinux, add curl to the Additional Library Dependencies line under Linker / Input in the VS project properties. Note that you enter just curl, VCLinux supplies the -l and the gcc linker expands it to the actual filename of libcurl.a (or libcurl.so if you're linking a shared library).

You do not normally have to specify the library search path since /usr/lib etc. are automatically on the library search path. On Debian 9 for example, libcurl.a is in /usr/lib/i386-linux-gnu. But if you install curl somewhere non-standard, add the path to Additional Library Directories under Linker / General. If you are installing curl from your Linux distribution, remember to install the development files as well; on Debian this is the package libcurl4-gnutls-dev .

curl is compatible with pkg-config so, as an alternative to entering the paths and library names directly, you can specify %24(pkg-config --cflags libcurl) in C++ / All Options / Additional Options and %24(pkg-config --libs libcurl) in Linker / All Options / Additional Options. Note that %24 is an encoded $ because otherwise Visual Studio tries (and fails) to interpret the string as a macro.

Answer 2

Is it because there's no h after the . in your include? Other than that, Visual Studio also needs to know the search path for your headers and libraries. It can search the build output or some of its default directories which are the VC++ directories. Beyond that you have to tell it where to search, by using some of the other menus close by.