g++

问题 I want to enable optimization in g++ without command line parameter. I know GCC can do it by writing #pragma GCC optimize (2) in my code. But it seems won't work in G++. This page may help: http://gcc.gnu.org/onlinedocs/gcc/Function-Specific-Option-Pragmas.html My compiler version: $ g++ --version g++ (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1 <suppressed copyright message> $ gcc --version gcc (Ubuntu/Linaro 4.6.1-9ubuntu3) 4.6.1 <suppressed copyright message> I worte some code like this: #pragma

问题 I have a project that makes massive use of templates. Recently the compilation time rose quite abruptly. I wonder if there's a way for seeing what classes / lines require the most time to be compiled by g++. Here is some output from -ftime-report Execution times (seconds) TOTAL : 0.30 0.05 0.37 9119 kB Execution times (seconds) garbage collection : 0.91 ( 6%) usr 0.00 ( 0%) sys 0.92 ( 5%) wall 0 kB ( 0%) ggc callgraph construction: 0.23 ( 2%) usr 0.11 ( 3%) sys 0.37 ( 2%) wall 10652 kB ( 1%)

问题 My Debian 7 armel embedded system currently has g++ 4.6, and I'd like to upgrade to g++ 4.9 to use new C++11 features. How do I do that? My current sources.list contents is: deb http://security.debian.org/ wheezy/updates main deb-src http://security.debian.org/ wheezy/updates main deb http://ftp.us.debian.org/debian wheezy main non-free deb-src http://ftp.us.debian.org/debian wheezy main non-free A simple apt-get install of the package does not work: root@arm:~# apt-get install g++-4.9

问题 The parameters -S -save-temps work fine, as long as i don't use them on files with the same name. Think of the following situation: I have a project with a main directory and a subdirectory with the name subDir and in both of the directories are files placed with the name file.c . If I now call gcc -S -save-temps file.cpp subDir/file.c only one intermediate file with the name file.i will be generated. That is the expected behaviour, as the man file of gcc tells me, that the intermediate files

问题 I basically have a class that depends on a non-type template parameter. I defined a casting so an object of non-type template parameter N can convert to another of M . I have a minimal example that can reproduce the situation: template<auto Integral> class Test{ public: typedef decltype(Integral) value_type; static constexpr value_type N = Integral; constexpr Test (const value_type& x = 0); template<auto Integral2> constexpr explicit operator Test<Integral2>() const; private: value_type n; };

问题 I basically have a class that depends on a non-type template parameter. I defined a casting so an object of non-type template parameter N can convert to another of M . I have a minimal example that can reproduce the situation: template<auto Integral> class Test{ public: typedef decltype(Integral) value_type; static constexpr value_type N = Integral; constexpr Test (const value_type& x = 0); template<auto Integral2> constexpr explicit operator Test<Integral2>() const; private: value_type n; };

问题 I want to run hello world written on C++ and compiled with Android toolchain 9 , but I faced with issue: by default I have no permissions to launch it and I can't change permissions using chmod`. I used Android 2.3.3 - Api Level 10 Application was compiled by cross compiler for API level 9 Procedure: Compile application: ~/toolchain_andr9/bin/ arm-linux-androideabi-g++ helloworld.cpp Then send application to SDCARD on the emulator: >adb push a.out /mnt/sdcard then go to SHELL and try to run a

问题 When I develop in C++ on a filesystem that is not case sensitive, I miss problems such as #include "File.h" if on disk it is actually file.h . The problem only appears when I eventually try to compile the code on a case sensitive filesystem. How do I simulate case sensitivity on a filesystem (such as OSX's default) that isn't case sensitive? Edit: I am looking for an automated solution, one that I can run now and in the future with "the push of a button". It also appears to be perfectly good

问题 In the process of using gprof to profile a C++ program I've written, I've noticed that the vast majority of execution time is spent in the function "frame_dummy". More precisely, the first entry in the flat profile from the output of gprof shows 76.38% of sample time spent in and 24611191 calls to a function with name frame_dummy. In short, I am trying to understand both what frame_dummy refers to -- as I do not have any function named as such -- as well as what this means for my optimization

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Returning unique_ptr from functions 20.7.1.2 [unique.ptr.single] defines copy constructor like this : // disable copy from lvalue unique_ptr(const unique_ptr&) = delete; unique_ptr& operator=(const unique_ptr&) = delete; So, why the following code compiles fine? #include <memory> #include <iostream> std::unique_ptr< int > bar() { std::unique_ptr< int > p( new int(4)); return p; } int main() { auto p = bar(); std