Page History

According to C99, Section 7.4 of C99

The header <ctype.h> declares several functions useful for classifying and mapping characters. In all cases the argument is an int, the value of which shall be representable as an unsigned char or shall equal the value of the macro EOF. If the argument has any other value, the behavior is undefined.

...

Compliance with this rule is complicated by the fact that the char data type mightcan, in any implementation, be signed or unsigned.

...

Note: XSI denotes an X/Open System Interfaces Extension to \[ISO/IEC 9945\] -- POSIX ^®^. The functions are not defined by C99.

A generalization of this rule is guideline Rule STR34-C. Cast characters to unsigned types before converting to larger integer sizesis a generalization of this rule.

Noncompliant Code Example

...

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

Related Guidelines

CERT C++ Secure Coding Standard: STR37-CPP. Arguments to character handling functions must be representable as an unsigned char

...

Wiki Markup\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 7.4, "Character handling <{{ctype.h>"

MITRE CWE: CWE-704, "Incorrect Type Conversion or Cast"

MITRE CWE: CWE-686, "Function Call With Incorrect Argument Type"

Bibliography

}}>"
\[[Kettlewell 2002|AA. Bibliography#Kettle 02]\] Section 1.1, "<{{ctype.h}}> And Characters Types"
\[[MITRE 2007|AA. Bibliography#MITRE 07]\] [CWE ID 704|http://cwe.mitre.org/data/definitions/704.html], "Incorrect Type Conversion or Cast," [CWE ID 686|http://cwe.mitre.org/data/definitions/686.html], "Function Call With Incorrect Argument Type"

...

STR36-C. Do not specify the bound of a character array initialized with a string literal      07. Characters and Strings (STR)      STR38-C. Do not use wide-char functions on narrow-char strings and vice versa