CERT C: Rule STR37-C

Arguments to character-handling functions must be representable as an unsigned char

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Description

Rule Definition

Arguments to character-handling functions must be representable as an unsigned char.¹

Polyspace Implementation

The rule checker checks for Invalid arguments to character-handling functions.

Examples

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Invalid arguments to character-handling functions

Issue

Invalid arguments to character-handling functions occurs when you use a signed or plain char variable with a negative value as argument to a character-handling function declared in ctype.h, for instance, isalpha() or isdigit().

Risk

You cannot use plain char variables as arguments to these character-handling functions. On certain platforms, plain char variables can have negative values that cannot be represented as unsigned char or EOF, resulting in undefined behavior.

Fix

To avoid unexpected results, explicitly cast plain char variables to unsigned char before passing to character-handling functions.

Check Information

Group: Rule 07. Characters and Strings (STR)

Version History

Introduced in R2019a

¹ This software has been created by MathWorks incorporating portions of: the “SEI CERT-C Website,” © 2017 Carnegie Mellon University, the SEI CERT-C++ Web site © 2017 Carnegie Mellon University, ”SEI CERT C Coding Standard – Rules for Developing safe, Reliable and Secure systems – 2016 Edition,” © 2016 Carnegie Mellon University, and “SEI CERT C++ Coding Standard – Rules for Developing safe, Reliable and Secure systems in C++ – 2016 Edition” © 2016 Carnegie Mellon University, with special permission from its Software Engineering Institute.

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