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Run‐time detection of undefined variables considered essential
Author(s) -
Kempton Willett,
Wichmann Brian A.
Publication year - 1990
Publication title -
software: practice and experience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 70
eISSN - 1097-024X
pISSN - 0038-0644
DOI - 10.1002/spe.4380200405
Subject(s) - pascal (unit) , computer science , compiler , variable (mathematics) , consistency (knowledge bases) , programming language , compile time , mathematics , artificial intelligence , mathematical analysis
Access to an undefined variable—one which has never been assigned a value—can be detected by automatic means. However, today's compilers do not detect undefined variables comprehensively, and the environment dependence of these errors often allows them to evade normal testing procedures. Language standards for Pascal, Modula‐2 and Ada specify the circumstances in which the undefined variable access should cause an error trap. The logic of undefined in these standards is compared, revealing problems in security, implementation effort and consistency with accepted programming practice. An alternative logic, ‘undefined if totally‐undefined’ is proposed.