我一度對於C語言與C++是不是開源語言很困惑：為什么有那么多人鼓吹Java、Python、PHP等是開源語言，卻沒有人提C與C++開源與否呢？今天在stackoverflow上找到了幾個比較滿意的回答，特寫篇博文總結一下老外的回答，也供各位對此問題持疑問態度的朋友一個參考。
關於C語言開源與否：
C語言是一個由ISO組織中的ANSI制定的標准，任何個人或者組織都可以根據這個標准將其實現。現今，世界上有許多不同的C語言實現，比較著名的有：GCC、Watcom、MS C等，其中前兩者是開源的，后者是閉源的。下面粘貼幾個老外的回答（鏈接：https://stackoverflow.com/questions/5099384/is-c-open-source）：
1 The C language is not a piece of software but a defined standard, so one wouldn't say that it's open-source, but rather that it's an open standard. 2
3 There are a gazillion different compilers for C however, and many of those are indeed open-source. The most notable example is GCC's C compiler, which is all under the GNU General Public License (GPL), an open-source license. 4
5 There are more options. Watcom is open-source, for instance. There is no shortage of open-source C compilers, but without a doubt the most widespread one, at least in the non-Windows world, is GCC. 6
7 For Windows, your best bet is probably Watcom or GCC by using Cygwin or MinGW.
1 C is a standard which specifies how C compilers should generate programs. 2 C itself doesn't have any source code, just like a musical note doesn't have any plastic. 3
4 Some C compilers, such as GCC, are open source.
1 C is just a language, and a standardised one at that, too. It pretty much is the compiler that "does all the work". Different compilers did have different dialects; before the the C99 ANSI standard, you had things like Borland C and other competing compilers, that implemented the C language in their own fantastic ways. 2
3 stdlib is just an agreed-upon collection of standard libraries that are required to be present in any ANSI C implementation.
關於C++開源與否：
與C語言類似，C++也是由ISO/ANSI制定的一個標准，所謂的“官方”並未提供確切的實現，任何組織與個人都可以根據標准自己開發一個C++編譯器出來。出名的C++編譯器有：GCC/G++、libc/libc++、clang（++）、 Visual studio和MS´ runtime等。也把老外的幾個回答貼出來（鏈接：https://stackoverflow.com/questions/22589213/is-c-an-open-source-project-which-community-developes-it）：
1 C++ itself is only a description what the language should be, 2 without a definite implementation. 3 Anyone can make his own implementations (compiler etc, runtime library, ...) 4 and call it C++ if it fits to the description. 5
6 http://www.open-std.org/jtc1/sc22/wg21/ 7
8 And if a implementation is open source depends on the creator. 9
10 Examples of implementation (parts): 11 GCC/G++, libc/libc++, clang (++ too), Visual studio and MS´ runtime...
1 C++ is developed by an ISO standard committee. There's also a C++ foundation that runs a web site you might want to read. 2
3 C++ itself is a language, not a specific implementation, so there's no source code available for the standard/language itself. 4
5 Some C++ implementations are open source (e.g., Gnu and Clang).
1 1. C++ is a code standard defined by the International Organization of Standardization (ISO). There are many different implementations of the language, but they all tend to conform to C++11. Unlike Linux or Qt, C++ is just a standard, and to use any code written in the language you'll need a compiler. The major compilers (list from Wikipedia) are LLVM Clang, GCC, Microsoft Visual C++, and the Intel C++ Compiler. 2 2. C++ revisions are dealt with by ISO, and are influenced primarily by the maintainers of the above four implementations. 3 3. Clang and GCC are both open-source, I'm sure if you poke around you can find other conforming compilers but those are the two most used.
總之，跟Java、Python和PHP這樣所謂的開源語言不同，C語言與C++沒有官方提供的各自確切的實現代碼（庫），ISO/ANSI僅僅提供了C和C++的標准。