浏览器可以⽤c语⾔编辑吗，如何在浏览器端运⾏cc++语⾔编写
的代码
安装依赖
Node.js(0.8 or above; 0.10.17 or above to run websocket-using servers in node):
Python2.x (2.7.3 or above preferred)
Java(1.6.0_31 or later). Java is optional. It is required to use theClosure Compiler(in order to minify your code).
Gitclient. Git is required if building tools from source.
Fastcomp(Emscripten’s fork of LLVM and Clang)
To build the Fastcomp code from source:
Create a directory to store the build. It doesn’t matter where, because Emscripten gets the information from thecompiler configuration file (~/.emscripten). We show how to update this file later in these instructi
ons:
mkdirmyfastcompcdmyfastcomp
Clone thekripken/emscripten-fastcomp-clangrepository intoemscripten-fastcomp/tools/clang:
Warning
Youmustclone it into a directory namedclangas shown, so thatClangis present intools/clang!
Create abuilddirectory (inside theemscripten-fastcompdirectory) and then navigate into it:
mkdirbuildcdbuild
Configure the build usingeithercmakeor theconfigurescript:
Usingcmake:
cmake..-DCMAKE_BUILD_TYPE=Release-DLLVM_TARGETS_TO_BUILD="X86;JSBackend"-
DLLVM_INCLUDE_EXAMPLES=OFF-DLLVM_INCLUDE_TESTS=OFF-DCLANG_INCLUDE_EXAMPLES=OFF-
DCLANG_INCLUDE_TESTS=OFF
Note
On Windows add the-G"VisualStudio10Win64"directive to build using Visual Studio (Visual Studio 2011 and 2012 do NOT work).
Usingconfigure(Linux/Mac only):
../configure--enable-optimized--disable-assertions--enable-targets=host,js
Determine the number of available cores on your system (Emscripten can run many operations in parallel, so using more cores may have a significant impact on compilation time):
On Mac OS X you can get the number of cores using:Apple menu | About this mac | More info | System report. TheHardware overviewon the resulting dialog includes aTotal number of coresentry.
On Linux you can find the number of cores by entering the following command on the
terminal:cat/proc/cpuinfo|grep"^cpucores"|uniq.
On Windows the number of cores is listed on theTask Manager | Performance Tab. You can open theTask Managerby enteringCtrl + Shift + Escfrom the Desktop.
Callmaketo build the sources, specifying the number of available cores:
make-j4
Note
If the build completes successfully,clang,clang++, and a number of other files will be created in the release directory
(/build/Release/bin).
The final step is to update the~/.emscriptenfile, specifying the location offastcompin theLLVM_ROOTvariable.
Note
If you’re building thewholeof Emscripten from source, following the platform-specific instructions inBuil
ding Emscripten from Source, you won’t yet have Emscripten installed. In this case, skip this step and return to those instructions.
If you already have an Emscripten environment (for example if you’re building Fastcomp using the SDK), then
setLLVM_ROOTto the location of theclangbinary under thebuilddirectory. This will be something
like/build/Release/binor/build/bin:
```
vim ~/.emscripten
```
修改 LLVM_ROOT到指定的⽂件⽬录
LLVM_ROOT = '/usr/local/myfastcomp/emscripten-fastcomp/build/bin' # directory
TheEmscripten code, from GitHub
clone emscripten项⽬到本地
```
cd emscripten
npm install
```
测试是否各依赖环境已经正确安装成功
在emscripten⽬录下运⾏
```
./emcc tests/hello_world.cpp
```
如果没有报错则会在同⽬录下到⼀个新⽂件a.out.js
现在可以通过nodejs来运⾏a.out.js这个⽂件了
```
node a.out.js
```
会在控制台打印出
```
hello, world!
```
通过browserify编译使之能在浏览器运⾏
安rowserify
```
sudo npm install browserify -g
```
编译a.out.js⽂件
```
browserify a.out.js > test.js
```
现在可以在⽹页中引⼊test.js⽂件
```
```
打开控制台可以看到
```
hello world
```
可以在输出的时候直接指定声称为浏览器端运⾏的代码，
./emcc tests/hello_world.cpp -o test.html
在js中调⽤c++/c写的函数
使⽤emscritpen输⼊代码优化
./emcc tests/hello-test.cpp -o function.js
代码是通过指定优化的优化参数运⾏时，EMCC。级别包括：-O0(不优化)，-O1，-O2，-Os，-OZ和-O3添加setting
-s EXPORTED_FUNCTIONS="['_uncompress']"  //到处函数
-s  NO_FILESYSTEM=1      //0 在代码中包含⽂件系统代码， 1在代码中不包含⽂件系统代码
-s EXPORTED_RUNTIME_METHODS    //到处可以在模块中使⽤的函数
[
'FS_createFolder',
'FS_createPath',
'FS_createDataFile',
'FS_createPreloadedFile',
'FS_createLazyFile',
'FS_createLink',
'FS_createDevice',
'FS_unlink',
'Runtime',
'ccall',
'cwrap',
'setValue',
'getValue',
'ALLOC_NORMAL',
'ALLOC_STACK',
'ALLOC_STATIC',
'ALLOC_DYNAMIC',
'ALLOC_NONE',
'allocate',
'getMemory',
'Pointer_stringify',
'AsciiToString',
'stringToAscii',
'UTF8ArrayToString', 'UTF8ToString',
'stringToUTF8Array',
'stringToUTF8',
'lengthBytesUTF8',
'stackTrace',
'addOnPreRun',
'addOnInit',
'addOnPreMain',
'addOnExit',
'addOnPostRun',
'intArrayFromString', 'intArrayToString',
'writeStringToMemory', 'writeArrayToMemory', 'writeAsciiToMemory',
'addRunDependency',
'removeRunDependency',
];
编译多个c++/c⽂件到⼀个js中
# Sub-optimal - JavaScript optimizations are omitted
./emcc -O2 a.cpp -o a.bc
./emcc -O2 b.cpp -o b.bc
.
/emcc a.bc b.bc -o project.js
# Sub-optimal - LLVM optimizations omitted
./emcc a.cpp -o a.bc
./emcc b.cpp -o b.bc
./emcc -O2 a.bc b.bc -o project.js
# Broken! Different JavaScript and LLVM optimisations used.
./emcc -O1 a.cpp -o a.bc
./emcc -O2 b.cpp -o b.bc
./emcc -O3 a.bc b.bc -o project.js
# Correct. The SAME LLVM and JavaScript options are provided at both levels. ./emcc -O2 a.cpp -o a.bc
./emcc -O2 b.cpp -o b.bc
cmake如何使用
./emcc -O2 a.bc b.bc -o project.js

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