How Does Unicode Impact C Source Code Encoding?

Unicode in C Source Code

C source code encoding is a multifaceted subject. Let's explore the nuances of character handling.

Every C compiler must support characters from the basic source character set. These include common characters like letters, digits, and punctuation. Additionally, compilers provide support for expressing characters not included in this set using universal-character-names (e.g., uffff, Uffffffff).

The mapping between characters in the source file and internal source characters used at compile time is implementation-defined. This mapping constitutes the encoding used. According to the C 98 standard:

Physical source file characters are mapped, in an implementation-defined manner, to the basic source character set (introducing new-line characters for end-of-line indicators) if necessary. Any source file character not in the basic source character set is replaced by the universal-character-name that designates that character.

GCC allows customization of the input character set using the -finput-charset=charset option. Similarly, the character set used at runtime can be modified using -fexec-charset=charset for char (defaulting to UTF-8) and -fwide-exec-charset=charset for wchar_t (defaulting to UTF-16 or UTF-32, depending on its size).

Non-ASCII characters, such as Chinese characters, can be used in comments and strings. For example, the following code is valid:

<code class="cpp">// Comment containing Chinese character: 中
wstring str = L"Strange chars: â Țđ ě €€";</code>

The full Unicode character set is supported, allowing the expression of a wide range of characters in source code.

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