For portable applications, use only the assignment = operator, the equality operators == and !=, and the unary & operator on plain-character-typed or plain-wide-character-typed expressions.
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- The binary
+operator may be used to add integer values 0 through 9 to'0'. - The binary
-operator may be used to subtract character 0. - Relational operators
<,<=,>, and>=can be used to check whether a character or wide character is a digit.
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In this example, the specific check is enforced using compliant operations on character expressions.:
| Code Block | ||||
|---|---|---|---|---|
| ||||
char ch = 't';
if ((ch == 'a') || (ch == 'b') || (ch == 'c')) {
/* ... */
}
|
Exceptions
STR09-C-EX0EX1: Consecutive values for characters like a~z can be assumed on platforms where ASCII or Unicode is used. This recommendation is primarily concerned with platform portability, for example, if code is migrated from ASCII systems to non-ASCII systems.
Risk Assessment
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
STR09-C |
Low |
Unlikely |
Low | P3 | L3 |
Automated Detection
Tool | Version | Checker | Description | ||||||
| Astrée |
| Supported indirectly via MISRA C:2012 rule 10.1. | |||||||
| Axivion Bauhaus Suite |
| CertC-STR09 | |||||||
| Helix QAC |
| C2106, C2107 | |||||||
| LDRA tool suite |
| 329 S | Fully implemented | ||||||
| Parasoft C/C++test |
| CERT_C-STR09-a | Expressions with type (plain) char and wchar_t shall not be used as operands to built-in operators other than =, ==, != and the unary & operator | ||||||
| PC-lint Plus |
| 9209 | Fully supported | ||||||
| RuleChecker |
| Supported indirectly via MISRA C:2012 rule 10.1. |
Related Guidelines
| SEI CERT C++ |
| Coding Standard | VOID STR07-CPP. Don't assume numeric values for expressions with type plain character |
Bibliography
| [Jones 2009] | Section 5.2.1, "Character Sets" |
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