C - Cmake compiling program with libcurl - c

Question

I'm trying to use some curl code to test the lib but I can't compile it :(
I'm using Clion (Cmake + gcc) and I've got a libcurl.a, a libcurl.dll and a libcurl.dlla
What am I suppose to do with those 3 files ?
This is my CmakeLists.txt :
cmake_minimum_required(VERSION 3.10)
project(curl_test2 C)
set(CMAKE_C_STANDARD 99)
ADD_DEFINITIONS( -DCURL_STATICLIB )
include_directories( "include" )
set(SRCS"
srcs/main.c")
set(HEADERS
"include/curl/curl.h"
"include/curl/easy.h")
link_directories("lib")
add_executable(curl_test2 ${SRCS} ${HEADERS})
target_link_libraries(curl_test2 "curl")
this is my project:
include
--curl
--curl.h
srcs
--main.c
lib
--libcurl.a
(--dlls
--libcurl.dll
--libcurl.dlla) <- i'm not using them for now
this is my main.c (just a libcurl example, not really important - i'm just trying to compile):
#include <stdio.h>
#include "curl/curl.h"
int main(void)
{
CURL *curl;
CURLcode res;
curl_global_init(CURL_GLOBAL_ALL);
curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "http://postit.example.com/moo.cgi");
curl_easy_setopt(curl, CURLOPT_POSTFIELDS, "name=daniel&project=curl");
res = curl_easy_perform(curl);
if(res != CURLE_OK)
fprintf(stderr, "curl_easy_perform() failed: %s\n",
curl_easy_strerror(res));
curl_easy_cleanup(curl);
}
curl_global_cleanup();
return 0;
}
When I'm trying to build the compiler drop this error : "undefined reference to `_imp__curl_global_init'" (and all other curl function calls)
Can you help me ? I'm a bit lost - I did not really use Cmake before..
Thank you !

Answer 1

You link with static curl library (libcurl.a) which required CURL_STATICLIB definition. Add this in your CMakeLists.txt between "project" and "add_executable" commands:
add_definitions( -DCURL_STATICLIB )
Moreover, your file .dlla is not .dll.a ? In that case, .dll.a file is (I think) generated by MinGW toolchain and is required only if you link dynamically with curl library (as .dll file).
I downloaded the sources of cURL library here and compiled it (with Visual Compiler 2015). It produces shared libraries (libcurl.dll and libcurl_imp.lib) that I move in the lib directory (I should rename libcurl_imp.lib to curl.lib). I move also the include directory.
Then, I used this CMakeLists.txt :
cmake_minimum_required(VERSION 3.10)
project(curl_test2 C)
set(CMAKE_C_STANDARD 99)
set(SRCS "srcs/main.c")
set( CURL_LIBRARY ${CMAKE_SOURCE_DIR}/lib )
set( CURL_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/include )
find_package( CURL )
include_directories( ${CURL_INCLUDE_DIRS} )
link_directories( ${CURL_LIBRARIES} )
add_executable(curl_test2 ${SRCS})
target_link_libraries(curl_test2 curl)
With it, your project compiles and the execution works.
I also tried with cURL static library (for that, if you use CMake to compile cURL, add -DCURL_STATICLIB=ON in cmake command line). And I moved the produced library libcurl.lib to lib\curl.lib.
I used this CMakeLists.txt :
cmake_minimum_required(VERSION 3.10)
project(curl_test2 C)
set(CMAKE_C_STANDARD 99)
set(SRCS "srcs/main.c")
add_definitions( -DCURL_STATICLIB )
set( CURL_LIBRARY ${CMAKE_SOURCE_DIR}/lib )
set( CURL_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/include )
find_package( CURL )
include_directories( ${CURL_INCLUDE_DIRS} )
link_directories( ${CURL_LIBRARIES} )
add_executable(curl_test2 ${SRCS})
target_link_libraries(curl_test2 curl wldap32 ws2_32)
And it works too.