According to subclause 6.2.7 of the C Standard [AA. Bibliography#ISO-ISO/IEC 9899-:2011],
All declarations that refer to the same object or function shall have compatible type; otherwise, the behavior is undefined.
(See also CC. Undefined Behavior#ub_undefined behavior 15 of Annex J.)
Further, according to subclause 6.4.2.1,
Any identifiers that differ in a significant character are different identifiers. If two identifiers differ only in nonsignificant characters, the behavior is undefined.
(See also CC. Undefined Behavior#ub_undefined behavior 31 of Annex J.)
Identifiers in mutually visible scopes must be deemed unique by the compiler to prevent confusion about which variable or function is being referenced. BB. Definitions#implementation Implementations can allow additional nonunique characters to be appended to the end of identifiers, making the identifiers appear unique while actually being indistinguishable.
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extern int *global_symbol_definition_lookup_table_a;
extern int *global_symbol_definition_lookup_table_b;
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Compliant Solution (Source Character Set)
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extern int *a_global_symbol_definition_lookup_table;
extern int *b_global_symbol_definition_lookup_table;
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Noncompliant Code Example (Universal Character Names)
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extern int *\U00010401\U00010401\U00010401\U00010401;
extern int *\U00010401\U00010401\U00010401\U00010402;
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Compliant Solution (Universal Character Names)
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extern int *\U00010401\U00010401\U00010401\U00010401;
extern int *\U00010402\U00010401\U00010401\U00010401;
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Risk Assessment
Nonunique identifiers can lead to abnormal program termination, denial-of-service attacks, or unintended information disclosure.
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Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CodeSonar |
| LANG.STRUCT.DECLTYPE | Global variable declared with different types | ||||||
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| Can detect some violations of this rule but cannot flag violations involving universal names | |||||||
| 17 D | Fully implemented | |||||||
| PRQA QA-C |
| 627, 776, 0777, 778, 0779 | Partially implemented |
Related Vulnerabilities
Search for BB. Definitions#vulnerability vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
| AA. Bibliography#ISO-ISO/IEC TR 24772-:2013 | Choice of Clear Names [NAI] Identifier Name Reuse [YOW] |
| AA. Bibliography#MISRA 12MISRA C:2012 | Rule 5.1 through Rule 5.5 (required) |
Bibliography
| [AA. Bibliography#ISO-ISO/IEC 9899-:2011] | Subclause 6.2.7, "Compatible Type and Composite Type" |
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