Is there an equivalent of -I (capital I) for object files in g++?

So that I don't have to put the full path in front of every object file. What would go instead of the -I command?

There is no gcc option like -I to add some directory to the object "search path", and there is no search path for objects. But there is search path for libraries (usually named lib*.a for static libraries and lib*.so for shared libraries in Unix world).

Directory-Options manual of gcc lists only -I option for include paths and -L option for library paths. There is no object path:

https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html#Directory-Options

And Link-Options manual of gcc mention only -L option (near -l description):

https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html#Link-Options

What can you use:

• shell variables or environment variables (in bash: OBJ_DIR=./path/to/dir then g++ ... $OBJ_DIR/obj1.o $OBJ_DIR/obj2.o)
• Packing several objects from single directory to single static library libSome_Long_Component_Name.a (this type of library is just like the archive of several *.o object files and some extra info made with ar rcs); then you can use g++ ... -Ldir/ -lSome_Long_Component_Name
• Makefiles and some variant of make utility (gnu make for linux and cygwin, nmake for windows's MSVC; you can start from gnu make manual: http://www.gnu.org/software/make/manual/make.html#Simple-Makefile then "2.4 Variables Make Makefiles Simpler" then "4.3 Types of Prerequisites" - with example of addprefix command to ask make find objects in some objdir. There is also VPATH special variable which instructs make to search sources and objects in several directories; but all objects in project should have different names).
• Some IDE with support of Unix projects (Code::Blocks, list1, list2, wikilist of C/C++ IDE?); they usually manage all sources of you project and are able to generate Makefiles for project.
• Some more modern build system, not the make: like CMake, SCons (or qmake if you use Qt).