Page History

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This noncompliant code example fails to test for conditions where a is neither b nor c. This behavior may be the correct in this case, but failure to account for all the values of a can result in logic errors if a unexpectedly assumes a different value.

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if (a == b) {
  /* ... */
}
else if (a == c) {
  /* ... */
}
else {
  /* handleHandle error condition */
}

Noncompliant Code Example (Switch)

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typedef enum { Red, Green, Blue } Color;
const char* f(Color c) {
  switch (c) {
    case Red: return "Red";
    case Green: return "Green";
    case Blue: return "Blue";
    default: return "Unknown color";   /* necessaryNecessary */
  }
}

Note that adding a default case to a switch statement, even when all possible switch labels are specified, is an exception (MSC07-EX1) to MSC07-C. Detect and remove dead code.

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typedef enum { Red, Green, Blue } Color;
const char* f(Color c) {
  switch (c) {
    case Red: return "Red";
    case Green: return "Green";
    case Blue: return "Blue";
  }
  return "Unknown color";   /* necessaryNecessary */
}

Historical Discussion

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#define ORIGINYEAR 1980
UINT32 days = /* numberNumber of days since January 1, 1980 */
int year = ORIGINYEAR;
/* ... */

while (days > 365) {
  if (IsLeapYear(year)) {
    if (days > 366) {
      days -= 366;
      year += 1;
    }
  }
  else {
    days -= 365;
    year += 1;
  }
}

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The following proposed rewrite is provided by at http://wwwwinjade.aeroxp.orgnet/2009/01/lesson-on-infinite-loops. The loop is guaranteed to exit, because days decreases for each iteration of the loop, unless the while condition fails , and the loop terminates.

#define ORIGINYEAR 1980
UINT32 days = /* inputInput parameter */
int year = ORIGINYEAR;
/* ... */

int daysThisYear = (IsLeapYear(year) ? 366 : 365);
while (days > daysThisYear) {
  days -= daysThisYear;
  year += 1;
  daysThisYear = (IsLeapYear(year) ? 366 : 365);
}

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  if (x > 0) {
	  /* ... */
  } else if (x < 0) {
    /* ... */
  } else if (x == 0) {
    /* ... */
  }

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

Related Guidelines

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Bibliography

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[Hatton 1995]

Section 2.7.2, "Errors of

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Omission and

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Addition"
[Viega 2005]	Section 5.2.17, "Failure to

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Account for

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Default Case in

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Switch"
[Zadegan 2009]	"A Lesson on Infinite Loops"

 http://www.aeroxp.org/2009/01/lesson-on-infinite-loops] for analysis on the Zune 30 bug