The C Standard, 7.2123.5.3, paragraph 7 [ISO/IEC 9899:20112024], places the following restrictions on update streams:
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The following scenarios can result in undefined behavior. (see See undefined behavior 151.):
- Receiving input from a stream directly following an output to that stream without an intervening call to
fflush(),fseek(),fsetpos(), orrewind()if the file is not at end-of-file - Outputting to a stream after receiving input from that stream without a call to
fseek(),fsetpos(), orrewind()if the file is not at end-of-file
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Alternately inputting and outputting from a stream without an intervening flush or positioning call is undefined behavior.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
FIO39-C | Low | Likely | Medium | P6 | L2 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| Supported, but no explicit checker | |||||||
| Axivion Bauhaus Suite |
| CertC-FIO39 | |||||||
| CodeSonar |
| IO.IOWOP | Input After Output Without Positioning | ||||||
| Compass/ROSE |
Can detect simple violations of this rule |
5.0
| Helix QAC |
| DF4711, DF4712, DF4713 | |||||||
| Klocwork |
| CERT.FIO.NO_FLUSH |
| LDRA tool suite |
| 84 D | Fully implemented | ||||||
| Parasoft C/C++test |
| CERT_C-FIO39-a | Do not alternately input and output from a stream without an intervening flush or positioning call | ||||||
| PC-lint Plus |
| 2478, 2479 | Fully supported | ||||||
| CERT C: Rule FIO39-C | Checks for alternating input and output from a stream without flush or positioning call (rule fully covered) |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
Key here (explains table format and definitions)
Taxonomy | Taxonomy item | Relationship |
|---|---|---|
| CERT C |
| FIO50-CPP. Do not alternately input and output from a file stream without an intervening positioning call | Prior to 2018-01-12: CERT: Unspecified Relationship | |
| ISO/IEC TS 17961:2013 | Interleaving stream inputs and outputs without a flush or positioning call [ioileave] | Prior to 2018-01-12: CERT: Unspecified Relationship |
| CWE 2.11 | CWE-664 | 2017-07-10: CERT: Rule subset of CWE |
CERT-CWE Mapping Notes
Key here for mapping notes
CWE-664 and FIO39-C
CWE-664 = Union( FIO39-C, list) where list =
- Improper use of an object (besides alternating reading/writing a file stream without an intervening flush
This CWE is vague on what constitutes “improper control of a resource”. It could include any violation of an object’s method constraints (whether they are documented or not). Or it could be narrowly interpreted to mean object creation and object destruction (which are covered by other CWEs).
Bibliography
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