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C99 supports The C standard supports universal character names that may be used in identifiers, character constants, and string literals to designate characters that are not in the basic character set. The universal character name \Unnnnnnnn designates the character whose eight-digit short identifier (as specified by ISO/IEC 10646) is nnnnnnnn. Similarly, the universal character name \unnnn designates the character whose four-digit short identifier is nnnn (and whose eight-digit short identifier is 0000nnnn).

C99C11, Section 5.1.1.2, Paragraph 4 para. 4 [ISO/IEC 9899:2011], says,

If a character sequence that matches the syntax of a universal character name is produced by token concatenation (6.10.3.3), the behavior is undefined.

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#define assign(uc1, uc2, val) uc1##uc2 = val;

int \u0401;
assign( \u04, 01, 4);

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GCC 4.3 on Linux refuses to compile this code; it complains of a "stray \," , referring to the universal character fragment in the invocation of the assign macro.

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#define assign(ucn, val) ucn = val;

int \u0401;
assign( \u0401, 4);

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

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CERT C++ Secure Coding Standard: PRE30-CPP. Do not create a universal character name through concatenation

ISO/IEC 10646-2003

ISO/IEC 9899:19992011 Section 5.1.1.2, "Translation phases," Section 6.4.3, "Universal character names," and Section 6.10.3.3, "The ## operator"

Bibliography

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