How do I solve these libcurl linking errors? - c++

Question

[Administrator#windows ~]$ g++ client.cpp -lcurl -o client.exe
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x23): undefined reference to `_imp__curl_global_init'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x5f): undefined reference to `_imp__curl_formadd'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x9b): undefined reference to `_imp__curl_formadd'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0xa2): undefined reference to `_imp__curl_easy_init'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0xc8): undefined reference to `_imp__curl_easy_setopt'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0xe4): undefined reference to `_imp__curl_easy_setopt'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0xf1): undefined reference to `_imp__curl_easy_perform'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x101): undefined reference to `_imp__curl_easy_cleanup'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x10e): undefined reference to `_imp__curl_formfree'
C:\DOCUME~1\ADMINI~1\LOCALS~1\Temp\ccKXFUtC.o:client.cpp:(.text+0x11b): undefined reference to `_imp__curl_slist_free_all'
collect2: ld returned 1 exit status
I don't have this problem on linux so I don't know why this happens on windows. I googled it already and didn't find anything except mailing list archives with the same question and reply saying "google it".
I'm using mingw. I did get some linker warnings when I built libcurl but they seemed to be ssl related and I don't know if it's a big deal because it built without errors.
*** Warning: linker path does not have real file for library -lssl.
*** I have the capability to make that library automatically link in when
*** you link to this library. But I can only do this if you have a
*** shared version of the library, which you do not appear to have
*** because I did check the linker path looking for a file starting
*** with libssl and none of the candidates passed a file format test
*** using a file magic. Last file checked: /ssl/lib/libssl.a
*** Warning: linker path does not have real file for library -lcrypto.
*** I have the capability to make that library automatically link in when
*** you link to this library. But I can only do this if you have a
*** shared version of the library, which you do not appear to have
*** because I did check the linker path looking for a file starting
*** with libcrypto and none of the candidates passed a file format test
*** using a file magic. Last file checked: /ssl/lib/libcrypto.a
*** Warning: linker path does not have real file for library -lz.
*** I have the capability to make that library automatically link in when
*** you link to this library. But I can only do this if you have a
*** shared version of the library, which you do not appear to have
*** because I did check the linker path looking for a file starting
*** with libz and none of the candidates passed a file format test
*** using a file magic. Last file checked: /mingw/lib//libz.a
*** The inter-library dependencies that have been dropped here will be
*** automatically added whenever a program is linked with this library
*** or is declared to -dlopen it.
*** Since this library must not contain undefined symbols,
*** because either the platform does not support them or
*** it was explicitly requested with -no-undefined,
*** libtool will only create a static version of it.

Answer 1

I was able to avoid these curl linking errors on windows (mingw win32) by adding option -lcurl.dll. -DCURL_STATICLIB was not needed in my case.
My build has two libcurl files in mingw/lib folder: libcurl.a and libcurl.dll.a

Answer 2

Libtool only built a static libcurl and not a dynamic library. Your headers are looking for a dynamic libcurl. It's probably not libcurl's fault, because I can see code in the headers that supports __declspec(dllimport) and __declspec(dllexport) (that's a good sign the package author knows what's what.
Technical details: see this answer regarding libssh.
Solution: Compile with -DCURL_STATICLIB.

Answer 3

Was having the same issue using netbeans 7.1 with mingw. From properties, linker adding library libcurl.dll.a solved the issue for me.
This file was located under curl-7.28.1\lib.libs after I ran the mingw make.

Answer 4

I had similar error (with libz and libsqlite) in different projects.
It is produced by GNU libtool script.
The reason in my case was lack of some files for these libraries (.la ?) or maybe libz.dll.a variants of the libraries.
To have all necessary files for automake/autoconf build ./configure --prefix=... ; make, you'll have to build zlib, crypto and ssl with configure and make to under the same MSYS.
cmake or custom makefile builds will usually not work as dependencies for shared-library autotool build.
Another and the most simple option is to build dynamic curl with cmake ( https://github.com/bagder/curl.git )