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In most cases, the only portable operators on plain char types are assignment and equality operators (=, ==, != ). An exception is the translation to and from digits. For example, if the char c is a digit, c - '0' is a value between 0 and 9.
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Noncompliant Code Example
The following non-compliant noncompliant code example simply shows calling the standard string handling function strlen() with a plain character string, a signed character string, and an unsigned character string:
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Compiling at high warning levels in compliance with [MSC00-AC. Compile cleanly at high warning levels] causes warnings to be issued when converting from {{unsigned char\[\]}} to {{const char const *}} when {{char}} is signed and from {{signed char\[\]}} to {{const char const *}} when {{char}} is defined to be unsigned. Casts are required to eliminate these warnings, but excessive casts can make code difficult to read and hide legitimate warning messages. |
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If this C code were compiled using a C+\+ compiler, conversions from {{unsigned char\[\]}} to {{const char const *}} and from {{signed char\[\]}} to {{const char const *}} would be flagged as errors requiring casts. |
Compliant Solution
The compliant solution uses plain char for character data.
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Conversions are not required and the code compiles cleanly at high warning levels without casts.
Risk Assessment
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
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STR04-A C | low | unlikely | low | P3 | L3 |
Automated Detection
Fortify SCA Version 5.0 with CERT C Rule Pack can detect violations of this recommendation, except cases involving signed char.
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
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\[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.2.5, "Types" \[[MISRA 04|AA. C References#MISRA 04]\] Rule 6.1, "The plain char type shall be used only for the storage and use of character values" |
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STR03-C. Do not inadvertently truncate a null-terminated byte string 07. Characters and Strings (STR) STR05-A. Use pointers to const when referring to string literals