I'm working on a fairly large project. When header files are touched, it results in 40 to several hundred files being compiled. This can take more than a few minutes. Since this invokes g++ separately for each .cpp file I thought I might be able to reduce the total compile time if I invoked g++ once with the entire list of .cpp files. There might be other overhead savings if g++ retains information about std C headers or pre-compiled headers between files. I don't know enough about g++ yet to tell if it does retain information, but I would like to find out. My problem is that if I pass all of the .cpp files to g++ at once, I have no way to tell g++ where to put the .o files. It wants to put them in the current working directory. I was hoping that g++ has some command line option that I am overlooking which allows the user to specify an output directory. Other command line compilers, Borland, CodeWarrior, and MSVC, have a command line option to specify the output directory for the .o files. I am looking for a similar feature in g++. This project has many different make files for sub-libraries, test programs, and interfaces. Our make system also likes to differentiate between debug, release, and profiled compilations so that it can put the .o files in appropriate directories. Therefore, dumping the .o files to the current working directory is not a good option. I can write a command to move the files to the appropriate directory, (which is probably what I will end up doing), but since I'm trying to eliminate steps here, I was hoping g++ could just put them where I wanted them to be placed. We also generate dependency files, so I will have to do something similar for the .d files as well. Im still kind of a newbee with g++. From what I have read, it seems as though g++ may invoke gcc separately for each file. If this is true, it might be better to use gcc rather than g++. I will be trying this out and doing some timings to see what I can do to improve compile times. I'll also be looking into pre-compiled headers and incremental linkage. If anyone has been down this road and has some insights or tips, I would appreciate hearing from you. Sincerely, Louie On Mon, 2006-04-10 at 13:01 -0500, Perry Smith wrote: > How about writing a shell script front end that would compile each > file separately? > > It may help us to help you if we understood why compiling separately > or moving the .o's does not work for you. > > HTH, > Perry > > On Apr 10, 2006, at 12:40 PM, Louie McCrady wrote: > > > g++ can take a collection of .cpp file names and compile them. I have > > not found a way to direct the placement of the resulting .o files to a > > specific directory. Is there an option that allows you to specify the > > directory where the .o files will be placed? > > > > When I compile a collection of .cpp files at one time, the .o files go > > to the current working directory. I would like to have them placed in > > an /obj directory somewhere else. > > > > I do not want to compile each .cpp file separately specifying both the > > input and output file locations. > > > > I do not want to compile to the current directory, then move the .o > > files to a separate /obj directory with a mv command. > > > > I've tried changing the current directory to the ./obj directory, but > > this throws off the location to other source, header, and lib files in > > other relative directories. This does not appear to be a practical > > solution. > > > > > > I need something like this: > > > > g++ -c foo1.cpp foo2.cpp foo3.cpp -o ./obj/ > > > > where foo1.o foo2.o foo3.o get placed in ./obj/ off the current > > working > > directory. > > > > Any help would be greatly appreciated. > > > > Thank you, > > > > Louie. > > > > > >
