Cmake complains about Could NOT find CURL (missing: CURL

I am building curl and curlpp from source in my CMakeLists.txt using FetchContent to use in an executable later in my CMakeLists.txt.

cmake_minimum_required(VERSION 3.17)
project(myproject VERSION 1.0.0)

include(FetchContent)
include(CMakePrintHelpers)

cmake_print_variables(CMAKE_CXX_FLAGS)

if (WIN32)
    set(CMAKE_USE_SCHANNEL ON)
endif()

# --- CURL
FetchContent_Declare(curl
        URL                    https://github.com/curl/curl/releases/download/curl-7_75_0/curl-7.75.0.tar.xz
        URL_HASH               SHA256=fe0c49d8468249000bda75bcfdf9e30ff7e9a86d35f1a21f428d79c389d55675 # the file hash for curl-7.75.0.tar.xz
        USES_TERMINAL_DOWNLOAD TRUE)
FetchContent_MakeAvailable(curl)

add_library(curl_int INTERFACE)
target_link_libraries(curl_int INTERFACE libcurl)
target_include_directories(curl_int INTERFACE ${curl_SOURCE_DIR}/include ${curl_BINARY_DIR}/include/curl)
add_library(CURL::mylibcurl ALIAS curl_int)
set(CURL_INCLUDE_DIR
        ${curl_SOURCE_DIR}/include
        )


# --- CURL C  
FetchContent_Declare(curlpp
        GIT_REPOSITORY  https://github.com/jpbarrette/curlpp.git
        )
FetchContent_MakeAvailable(curlpp) # ----> Error occurs here
cmake_print_variables(curlpp_SOURCE_DIR curlpp_BINARY_DIR)
add_library(curlpp_int INTERFACE)
target_link_libraries(curlpp_int INTERFACE libcurlpp CURL::mylibcurl)
target_include_directories(curlpp_int INTERFACE ${curlpp_SOURCE_DIR}/include ${curlpp_BINARY_DIR}/include/curl)
add_library(CURLPP::mylibcurlpp ALIAS curlpp_int)
set(CURLPP_INCLUDE_DIR
        ${curlpp_SOURCE_DIR}/include
        )
set(CURLPP_LIB_DIR
        ${curlpp_BINARY_DIR})

cmake_print_variables(CURLPP_LIB_DIR)
cmake_print_variables(CURLPP::mylibcurlpp)

# The rest of CMakeLists.txt is omitted

However, during cmake build, when it executes FetchContent_MakeAvailable(curlpp), I get a complaint about

Could NOT find CURL (missing: CURL_LIBRARY)

I am linking curlpp with curl by target_link_libraries(curlpp_int INTERFACE libcurlpp CURL::mylibcurl) and was expecting it to be able to find it.

How could I solve this?

CodePudding user response：

You can try adding this line after setting the CURL_INCLUDE_DIR:

find_library(CURL_LIBRARY NAMES curl PATHS ${curl_BINARY_DIR}) target_link_libraries(curl_int INTERFACE ${CURL_LIBRARY})

This will search for the curl library in the specified directory and link it to your curl_int target.

CodePudding user response：

In the CMake of curlpp, the CURL library is required and fetched if not available:

71 message(STATUS "Looking for CURL")
72 find_package(CURL REQUIRED)
73
.  if(CURL_FOUND)
.    message(STATUS "Found CURL version: ${CURL_VERSION_STRING}")
.    message(STATUS "Using CURL include dir(s): ${CURL_INCLUDE_DIRS}")
.    message(STATUS "Using CURL lib(s): ${CURL_LIBRARIES}")
.  else()
.    message(STATUS "Fetching CURL")
.    include(FetchContent)
.    FetchContent_Declare(CURL GIT_REPOSITORY https://github.com/curl/curl.git)
.    FetchContent_MakeAvailable(CURL)
.  endif()

https://github.com/jpbarrette/curlpp/blob/master/CMakeLists.txt#L72

I could think of two problems here, but also more information might be helpful, for example, if your error is thrown in line 72 or above that.

One option would be, that you build CURL into a directory that then is not found in the curlpp find_package call.
Another option would be that your versions are not compatible, looking at the code from curlpp they by default would download the master repo of curl.