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To guarantee header file names are unique, all included files should differ (in a case insensitive manner) in their first eight characters or in their (one character) file extension.
Non-Compliant Code Example
The following non-compliant code contains references to headers that may exist independently in various environments, but can be ambiguously interpreted by a C99-compliant compiler.
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Library.h and library.h may refer to the same file. Also, because only the first eight characters are guaranteed to be significant, it is unclear whether utilities_math.h and utilities_physics.h are parsed. Finally, a file such as my_libraryOLD.h exists, it may inadvertently be included instead of my_library.h.
Compliant Solution
This compliant solution avoids the ambiguity by renaming the associated files to be unique under the above constraints.
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The only solution for mitigating ambiguity of a file such as my_libraryOLD.h is to rename old files with either a prefix (that would fall within the first eight characters) or to add an extension (such as my_library.h.old).
Risk Assessment
Failing to guarantee uniqueness of header files may result in the inclusion of an older version of a header file, which may include incorrect macro definitions, obsolete function prototypes, or result in other errors that may or may not be detected by the compiler. Portability issues may also stem from the use of header names that are not guaranteed to be unique.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
PRE31-C | 1 (low) | 1 (unlikely) | 1 (high) | P1 | L3 |
References
| Wiki Markup |
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\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 6.10.2 "Source file inclusion" |