[question] packaging C library - linking failing on a project that tries to use it

Hello,

I am trying to build an external C library and I followed the various guides. Specifically: https://docs.conan.io/en/latest/howtos/makefiles.html

The library in question is https://github.com/fanf2/hg64

my conanfile is the following:

from conans import ConanFile, AutoToolsBuildEnvironment
from conans import tools

class Hg64(ConanFile):
    name = "hg64"
    version = "1.0.0"

    description = "A sketches histogram library."
    topics = ("performance", "histograms", "quantiles")
    homepage = "https://github.com/fanf2/hg64"
    license = "SPDX"
    settings = "os", "arch", "compiler", "build_type"

    _source_subfolder = "source_subfolder"

    def export_sources(self):
        for patch in self.conan_data.get("patches", {}).get(self.version, []):
            if "patch_file" in patch:
                patch_file = patch["patch_file"]
                self.copy(patch_file)

    def source(self):
        tools.get(**self.conan_data["sources"][self.version], destination=self._source_subfolder, strip_root=True)
        for patch in self.conan_data.get("patches", {}).get(self.version, []):
            if "patch_file" in patch:
                print(f"patching patch_file: {patch['patch_file']}")
                tools.patch(**patch, base_path=self._source_subfolder)

    def build(self):
        with tools.chdir("source_subfolder"):
            atools = AutoToolsBuildEnvironment(self)
            atools.make()
            self.run("ar -rcs libhg64.a random.o hg64.o")

    def package(self):
        self.copy("*.h", dst="include", src="source_subfolder")
        self.copy("*.a", dst="lib")

    def package_info(self):
        self.cpp_info.includedirs = ["include"]

I build it as follows:

conan create gsr/hg64/conanfile.py company/master -pr:b=default -pr:h=default  -s "&:build_type=Release"

and it creates the package successfully. If I look at the folder where it installed it, I see what I am expecting:

dabe@af41c569972b:~/conan/conan-packages/recipes (hg64)$ ll /home/dabe/.conan/data/hg64/1.0.0/_/_/package/7ad4b4ec31d9148d733986b5f567502885e20657/include/
total 16
-rw-r--r-- 1 dabe dabe 1061 Oct 14 17:39 random.h
-rw-r--r-- 1 dabe dabe 3420 Oct 14 17:39 hg64.h
drwxr-xr-x 2 dabe dabe 4096 Oct 14 17:50 .
drwxr-xr-x 4 dabe dabe 4096 Oct 14 17:50 ..
dabe@af41c569972b:~/conan/conan-packages/recipes (hg64)$ ll /home/dabe/.conan/data/hg64/1.0.0/_/_/package/7ad4b4ec31d9148d733986b5f567502885e20657/lib/    
total 112
-rw-r--r-- 1 dabe dabe 103214 Oct 14 17:50 libhg64.a
drwxr-xr-x 4 dabe dabe   4096 Oct 14 17:50 ..
drwxr-xr-x 2 dabe dabe   4096 Oct 14 17:50 .

Now the real problem is that when I try to use it from another project, I am able to find the headers, but the library doesn’t link.

I use it like this on another project:

conan install .. company/master  --profile=company-default  -s '&:build_type=Debug'

The error is pretty self explanatory:

ld.lld: error: undefined symbol: hg64_destroy(hg64*)

and if I look at the generated compilation line, I see no mention of my library.

In my Cmake I use it as:

find_package(hg64 REQUIRED)

SET(TARGET_LINK_LIBS
        hg64::hg64

Cmake itself runs fine, so I expect that the generated files in the generator folder might not be correct. I am sure it might be a very small mistake, some expert eye could find quickly.

if I describe the package I have:

dabe@af41c569972b:~/gsr/conan/conan-packages/recipes (hg64)$ conan search hg64/1.0.0@company/master
Existing packages for recipe hg64/1.0.0@company/master:

    Package_ID: 7ad4b4ec31d9148d733986b5f567502885e20657
        [settings]
            arch: x86_64
            build_type: Release
            compiler: gcc
            compiler.libcxx: libstdc++11
            compiler.version: 10.3
            os: Linux
        Outdated from recipe: False

which seems a bit light

Is there anything odd in my recipe?

Thank you in advance

• [ X ] I’ve read the CONTRIBUTING guide.

[memsharded]

Happy to hear that! Then I am closing this ticket, don’t hesitate to open new ones for any further questions.

[davidebenato]

thank you @memsharded very helpful advice. It turns out my problem wasn’t really related to conan. My library is a C library and although I managed to package it correctly after your suggestions, I was not including it properly from C++

extern "C" {
#include <hg64.h>
}

fixed the problem. Thanks to your suggestion I will definitely include a test package as well.