problem with order of -lmylibrary flags.

[Ian Lance Taylor]

Brendan Miller <catphive@catphive.net> writes:

> I've found kind of a weird issue where if I indicate I want to link a
> library with the -l flag too early on the command line, I get linker
> errors.
>
> Here's an example:
> g++ -lml -lcvaux -lhighgui -lcv -lcxcore   -std=c++0x -Werror -Wall -g
> -MMD -MP -Iinclude  -o objrec main.cpp
>
> Here I'm linking a bunch of libraries, into a binary called objerec.
> The source file is at the end. This command line produces linker
> errors as if the libraries had not been linked properly.
>
> However in this example everything is fine:
> g++  -std=c++0x -Werror -Wall -g -MMD -MP -Iinclude  -o objrec
> main.cpp -lml -lcvaux -lhighgui -lcv -lcxcore
>
> The only difference is that I place the -l flags after the source file
> (main.cpp) that I'm building.
>
> Why does the second example compile while the first gets linker errors?

That is how the linker works.  The placement of -l options is
significant.  A -l option only resolves undefined symbols in objects
seen before the -l option.


> A more general question: in a make file is it better to list libraries
> you want to link in the LDFLAGS variable, or in the LDLIBS variable?

The LDLIBS variables, which in most Makefiles is simply called LIBS.

Ian