Page History

...

Restriction of the significance of an external name to fewer than 255 characters in the standard (considering each universal character name or extended source character as a single character) is an obsolescent feature that is a concession to existing implementations. As a result, it is not necessary to comply with this restriction as long as the identifiers are unique and the assumptions concerning the number of significant characters are documented.

Noncompliant Code Example (Source Character Set)

On implementations that support only the minimum requirements for significant characters required by the standard, this code example is noncompliant because the first 31 characters of the external identifiers are identical:

extern int *global_symbol_definition_lookup_table_a;
extern int *global_symbol_definition_lookup_table_b;

Compliant Solution (Source Character Set)

In a compliant solution, the significant characters in each identifier must differ:

extern int *a_global_symbol_definition_lookup_table;
extern int *b_global_symbol_definition_lookup_table;

Noncompliant Code Example (Universal Character Names)

In this noncompliant code example, both external identifiers consist of four universal character names. Because the first three universal character names of each identifier are identical, both identify the same integer array on implementations that support only the minimum requirements for significant characters required by the standard:

extern int *\U00010401\U00010401\U00010401\U00010401;
extern int *\U00010401\U00010401\U00010401\U00010402;

Compliant Solution (Universal Character Names)

For portability, the first three universal character name combinations used in an identifier must be unique:

extern int *\U00010401\U00010401\U00010401\U00010401;
extern int *\U00010402\U00010401\U00010401\U00010401;

Risk Assessment

Nonunique identifiers can lead to abnormal program termination, denial-of-service attacks, or unintended information disclosure.

Automated Detection

Related Vulnerabilities

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

Related Guidelines

Bibliography

...