Page History

...

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

...

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

...

The following noncompliant code example fails to consider all possible cases. Failure to account for all valid values of type Color will result in a logic error. Since valid values of an enumerated type include all those of its underlying integer type, unless enumeration constants have been provided for all those values, the default label is appropriate and necessary.

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";
  }
}

void g() {
  Color unknown = (Color)123;
  puts(f(unknown));
}

...

Microsoft Visual C++ .NET with /W4 does not warn when assigning an integer value to an enum type , or when the switch statement does not contain all possible values of the enumeration.

Compliant Solution (Switch)

The following compliant solution below takes care to provide the default label to handle all valid values of type Color:

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";   /* necessary */
  }
}

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

An alternative compliant solution to the noncompliant code example above is to provide a return statement after the switch statement. Note, however, that this solution may not be appropriate in all situations.

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";   /* necessary */
}

...

These two practices have now been merged. A switch on an enum type should now contain a case label for each enum value , but should also contain a default label for safety. This is not more difficult to analyze statically.

...

#define ORIGINYEAR 1980
UINT32 days = /* number 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;
  }
}

...

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

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

...

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

Related Vulnerabilities

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

...

CERT C++ Secure Coding Standard: MSC01-CPP. Strive for logical completeness

ISO/IEC TR 17961 (Draft) Use of an implied default in a switch statement [swtchdflt]

ISO/IEC TR 24772 "CLL Switch statements and static analysis"

...