compiler-flags

I am just starting with g++ compiler on Linux and got some questions on the compiler flags. Here are they Optimizations I read about optimization flags -O1 , -O2 and -O3 in the g++ manual page. I didn't understood when to use these flags. Usually what optimization level do you use? The g++ manual says the following for -O2 . Optimize even more. GCC performs nearly all supported optimizations that do not involve a space-speed tradeoff. The compiler does not perform loop unrolling or function inlining when you specify -O2. As compared to -O, this option increases both compilation time and the

We are using an third party static library, let say A.a for android development. We link it as shared library and it works fine in the one App, but when use B.so to build another C.so , some symbols in A.a cannot find. We have already use -Wl,--export-dynamic and -Wl,--whole-archive to build B.so . We have using nm to check those symbols, it exist but list as “t” instead of “T” ，which means it is local symbols instead of external. Seams the A.a are build with -fvisibility=hidden after som investigation. But because some reason it is hard for us to got an new build library immediately, so we

My build requires that I issue the following commands: $ g++ sniff.cpp -o sniff -lcrafter However, in my Eclipse build, all the complier gets is: g++ -o "sniffer_crafter" ./src/sniffer_crafter.o After getting these commands it complains that I have an undefined reference to the library Crafter. How can I resolve this linking issue using Eclipse? I have seen others answers to similar questions, but they don't seem to address Eclipse's current layout. I'm using the most recent edition of Eclipse Kepler. Include libraries:- right click on the project --> Goto Properties then goto --> C/C++ Build

When compiling the benchmark code below with -O3 I was impressed by the difference it made in latency so i began to wonder whether the compiler is not "cheating" by removing code somehow. Is there a way to check for that? Am I safe to benchmark with -O3 ? Is it realistic to expect 15x gains in speed? Results without -O3 : Average: 239 nanos Min: 230 nanos (9 million iterations) Results with -O3 : Average: 14 nanos, Min: 12 nanos (9 million iterations) int iterations = stoi(argv[1]); int load = stoi(argv[2]); long long x = 0; for(int i = 0; i < iterations; i++) { long start = get_nano_ts(); //

I need to compile a Java program on the command line, and I am trying to set the compiler level to a lower one (1.6). I tried like this but it didn't work: javac -1.6 Hello.java Use -source and -target options: javac -target 1.6 -source 1.6 Hello.java Nayuki Use: javac -source 1.6 -target 1.6 Hello.java This information comes from running javac -help : Usage: javac <options> <source files> where possible options include: -g Generate all debugging info -g:none Generate no debugging info -g:{lines,vars,source} Generate only some debugging info -nowarn Generate no warnings -verbose Output

I was a little confused with the responses to Quick way to override -Werror flag? So I ask my specific question here. I have multiple Makefiles working together and CFLAGS has been set along the way to (-Werror -Wall .. and many others) But in one of the Makefiles, I wish that the errors not be treated as warnings and so I would like to remove -Werror flag. What would be the best way to achieve this, so that only for this Makefile, -Werror flag is removed and for the others normal execution takes place? Thanks, Sunny Simpler way It looks like you can invoke gcc -c ... -Werror ... -Wno-error ..

With Xcode 4.2 and the LLVM compiler, when compiling for ARMv6 there are some very weird bugs in the generated application (such as "width" property of CGSize returning the "height" instead). To fix this, I found I must set the compiler flag -mno-thumb. I know how to set compiler flags on a file-by-file basis, but is there a way to set a compiler flag for the entire project? You can set project wide compiler flags in the project settings under the "Language" section of the "Build Settings" tab. 来源： https://stackoverflow.com/questions/7932834/xcode-project-wide-compiler-flag