Apple announced Xcode 4.3 for OSX Lion and 4.4 for OSX Mountain Lion last week. The major difference is that Xcode no longer provide an installer which is good thing because you now could update Xcode with AppStore in the future, plus it is much easier to carry the development environment with you. However, there is a little problem with this new version of Xcode, is that all command line toolsets and compilers are not visible in terminal.
这段话说的是新版的Xcode已经改成直接拖动到Application里边而不是以前的必须一步步安装：好处是方便，坏处是gcc/g++等命令都识别不了了。
解决办法：
1.自己将这些命令添加到环境变量：
export PATH=/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:$PATH Please be noted that clang does not reside in /Developer/usr/bin, it is now in /Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin Now you could access to gcc, g++, git or any toolsets bundled with Xcode. For your convenience, it is recommended to include it in your .bash_profile.
2.最简单不过了，安装Xcode命令行工具：写本文是已经是Xcode 5了：在Preference里边有Downloads可以下载，如果没有下载，可以到www.apple.com-->支持，按名称搜索：CommandLine工具、命令行工具，下载安装即可。