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ISO/IEC 9899:1999 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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PRE13-C. Avoid changing control flow in macro definitions 01. Preprocessor (PRE) PRE31-C. Avoid side-effects in arguments to unsafe macros