Brendan Miller <catphive@xxxxxxxxxxxx> 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
