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The examples here fall under the exception MSC17-C-EX2 in MSC17-C. Finish every set of statements associated with a case label with a break statement.
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When i = 1, the entire for loop is executed. When i = 2, two increments to j are made before the loop starts. When i = 3, one increment to j is made before the loop starts. The default case is no loop. Consequently, the function has the following behavior:
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|---|---|
1 | 12 |
2 | 12 |
3 | 11 |
Other values | 0 |
Compliant Solution
The compliant solution separates the switch and for blocks:
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| Code Block | ||||
|---|---|---|---|---|
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int n = (count + 7) / 8;
switch (count % 8) {
case 0: *to = *from++; /* Fall through */
case 7: *to = *from++; /* Fall through */
case 6: *to = *from++; /* Fall through */
case 5: *to = *from++; /* Fall through */
case 4: *to = *from++; /* Fall through */
case 3: *to = *from++; /* Fall through */
case 2: *to = *from++; /* Fall through */
case 1: *to = *from++; /* Fall through */
}
while (--n > 0) {
*to = *from++;
*to = *from++;
*to = *from++;
*to = *from++;
*to = *from++;
*to = *from++;
*to = *from++;
*to = *from++;
}
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Risk Assessment
Recommendation | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MSC20-C | Medium | Probable | Medium | P8 | L2 |
Automated Detection
Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| switch-label | Fully checked | ||||||
| CodeSonar |
| LANG.STRUCT.SW.MPC | Misplaced case | ||||||
| CC2.MSC20 | Fully implemented | |||||||
| Helix QAC |
| C2019 | |||||||
| LDRA tool suite |
| 245 S | Fully implemented |
| PC-lint Plus |
| 646, 9055 | Fully supported | ||||||
| Polyspace Bug Finder |
| CERT C: Rec. MSC20-C | Checks for situations where switch label is not at the outermost level of switch statement body (rec. fully covered) | ||||||
| RuleChecker |
| switch-label | Fully checked | ||||||
| SonarQube C/C++ Plugin |
| S1036 |
Related Guidelines
| SEI CERT C++ Coding Standard | VOID MSC20-CPP. Do not use a switch statement to transfer control into a complex block |
| ISO/IEC TR 24731-1:2007 |
| MISRA C:2012 |
| Rule 16.2 (required) |
Bibliography
| [ISO/IEC 9899:2011] | Subclause 6.8.6.1, "The goto Statement" |
| [Duff 1988] | Tom Duff on Duff's Device |
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