Using the UE5.4 built-in Libcurl.lib in a plugin (w/ no unresolved external references)

Development Programming & Scripting C++
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1

Here’s another example of using a third-party library in a plugin. In this case, the built-in (to UE5.4) third-party static libcurl.lib is added to a plugin. Note that simply using PublicAdditionalLibraries.Add() is not enough to satisfy the linker during compilation nor does it initialize libcurl correctly. Make the following addition to PluginName.Build.cs:

    PublicDefinitions.Add("WITH_LIBCURL=1");  // This is required
    PublicDefinitions.Add("CURL_STATICLIB=1");  // This is required when using static libcurl.lib
    string LibCurlPath = Target.UEThirdPartySourceDirectory + "libcurl/8.4.0/include/curl/";
    PublicSystemIncludePaths.Add(LibCurlPath); // located in the UE5.4 engine (not the project)   PublicAdditionalLibraries.Add(Target.UEThirdPartySourceDirectory+"libcurl/8.4.0/lib/Win64/Release/libcurl.lib");
    AddEngineThirdPartyPrivateStaticDependencies(Target, new string[]
		{
			"nghttp2",
			"OpenSSL",
			"zlib"
		});  // libcurl.lib has additional dependencies (from libcurl.Build.cs)
    PublicIncludePaths.Add($"{LibCurlPath}");

In the StartupModule(), or at the beginning of your code, add:

curl_global_init(CURL_GLOBAL_DEFAULT);

In the ShutdownModule(), or at the end of your code, add:

curl_global_cleanup();

These changes will solve any “unresolved external reference” errors and initialize/shutdown libcurl.

1 Like
2

Thanks for this post. He helped me solve the problem. I first enabled CURL as

PublicDependencyModuleNames.AddRange(
new string[]
{
"Core",
"libcurl"
}
);

It works, but UE 5 has not seen the include “curl.h” file. And only your message helped to fix the problem. It may also be useful to specify the desired CURL version. You can watch it. Example: D:\EG\Epic Games\UE_5.7\Engine\Source\ThirdParty\libcurl\