According to subclause 6.2.7 of the C Standard [ISO/AA. Bibliography#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 undefined behavior CC. Undefined Behavior#ub_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 undefined behavior CC. Undefined Behavior#ub_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. Implementations Definitions#implementation 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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| Code Block | ||||||
|---|---|---|---|---|---|---|
| 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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| Code Block | ||||||
|---|---|---|---|---|---|---|
| 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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| Code Block | ||||
|---|---|---|---|---|
| ||||
extern int *\U00010401\U00010401\U00010401\U00010401;
extern int *\U00010401\U00010401\U00010401\U00010402;
| ||||
Compliant Solution (Universal Character Names)
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| Code Block | ||||||
|---|---|---|---|---|---|---|
| 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 | ||||||
|
| 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 vulnerabilities BB. Definitions#vulnerability resulting from the violation of this rule on the CERT website.
Related Guidelines
| ISO/AA. Bibliography#ISO-IEC TR 24772:-2013 | Choice of Clear Names [NAI] Identifier Name Reuse [YOW] |
| MISRA C:2012AA. Bibliography#MISRA 12 | Rule 5.1 through Rule 5.5 (required) |
Bibliography
| [ISO/AA. Bibliography#ISO-IEC 9899:-2011] | Subclause 6.2.7, "Compatible Type and Composite Type" |
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