Cross compiled C Windows libcurl doesn't get linked correctly on Ubuntu
I am currently trying to cross compile libcurl in c for Windows 32x on Ubuntu 64x 14.04. After a bit of research I followed these steps:
1) Download library from https://curl.haxx.se/download.html
2) Go into extracted libcurl folder and execute:
./configure --host=i686-w64-mingw32 --build=i686-pc-linux-gnu --prefix=/usr/i686-w64-mingw32/ --enable-static --disable-shared
3) Execute: make
4) Execute: sudo make install
Then I added these include statements:
#include <winsock2.h> // Needed for curl
#include <windows.h> // Windows API
#include <curl/curl.h>
int main(int argc, char** argv)
{
CURL *curl;
CURLcode response;
char url[] = "someurl.com";
curl = curl_easy_init();
if(curl)
{
curl_easy_setopt(curl, CURLOPT_URL, url); //set url options
/* Perform the request, res will get the return code */
response = curl_easy_perform(curl);
if(response != CURLE_OK)
{
//Do something
}
/* always cleanup */
curl_easy_cleanup(curl);
}
return 0;
}
Now I tried to compile my code with following arguments:
i686-w64-mingw32-gcc main.c -o main.exe -L/usr/i686-w64-mingw32/lib -lcurl
The compiler returned following error code:
/tmp/ccebLf6U.o:main.c:(.text+0x336): Not defined reference to `_imp__curl_easy_init'
/tmp/ccebLf6U.o:main.c:(.text+0x365): Not defined reference to `_imp__curl_easy_setopt'
/tmp/ccebLf6U.o:main.c:(.text+0x372): Not defined reference to `_imp__curl_easy_perform'
/tmp/ccebLf6U.o:main.c:(.text+0x3f4): Not defined reference to `_imp__curl_easy_cleanup'
collect2: error: ld returned 1 exit status
Has someone an idea on how to fix this ?
[EDIT]
Something really interesting I stumbled upon is that if you call curl-config you get a bunch of compiler options.
Cross-Compiling library Using --prefix you are defining the the toplevel installation directory.
Libs will be placed into /usr/i686-w64-mingw32/lib
Same thing for includes files they will be placed /usr/i686-w64-mingw32/include
Using -L/usr/i686-w64-mingw32/ you are pointing the wrong path for libraries and cross-compiler cannot find libcurl
To point to the correct include location you have to add -I/usr/i686-w64-mingw32/include to your command.
At the end you compiled curl libs static only then you want to compile them statically: add -static to your command.
SO the correct command will be:
i686-w64-mingw32-gcc -static -I/usr/i686-w64-mingw32/include -L/usr/i686-w64-mingw32/lib -lcurl main.c -o main.exe
From the curls FAQ:
If you get linker error like "unknown symbol __imp__curl_easy_init ..." you have linked against the wrong (static) library. If you want to use the libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of the import libraries below. These are the libraries produced by the various lib/Makefile.* files:
Target: static lib. import lib for libcurl*.dll.
-----------------------------------------------------------
MingW: libcurl.a libcurldll.a
MSVC (release): libcurl.lib libcurl_imp.lib
MSVC (debug): libcurld.lib libcurld_imp.lib
Borland: libcurl.lib libcurl_imp.lib
Try path to linker -lcurl_imp or -llibcurl_imp
Update : Here is write flags on my Ubuntu with MinGW64:
i686-w64-mingw32-g++ -o app.exe objects.a -Lexternals/curl-7.39.0/lib -llibcurl_imp
Why I use libcurl_imp.lib instead libcurldll.a as described in table above? Becouse I build curl with cmake which make libcurl_imp.lib . So you should check name of built library.
So my solution to this problem probably lies right here: Cross compile tips for libraries
These are some tips and tricks for the cross compilation compiler mingw32 and the compilation of curl with my missing argument -DCURL_STATICLIB. I didn't test this out though because I solved the problem without curl.
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