# V796. A 'break' statement is probably missing in a 'switch' statement.

The analyzer has detected a 'switch' statement with a missing 'break' statement in one of its branches. When executing this code, the control flow will move on to the next 'case'. This is probably a typo, and 'break' is needed.

Consider the following example:

    for (char c : srcString)
    {
      switch (c)
      {
        case 't':
          *s++ = '\t';
          break;

        case 'n':
          *s++ = '\n';
          break;

        case 'f':
          *s++ = '\f'; // <=

        case '0':
          *s++ = '\0';
      }
    }

If it is a mistake, then you should add 'break' statement. If there is no error, then you should leave a hint to the analyzer and your colleagues, who will maintain the code in the future.

There are a number of ways to specify that this behavior is intentional. One way is to add a comment:

    case A:
      foo();
      // fall through
    case B:
      bar();

'fallthrough' attributes are also supported:

    __attribute__((fallthrough));
    [[fallthrough]];
    [[gnu::fallthrough]];
    [[clang::fallthrough]];

The diagnostic also implements several heuristic rules that reduce false positives. For example, when unrolling a loop:

    switch(num) {
         case 3:
               sum += arr[i + 2];
         case 2:
               sum += arr[i + 1];
         case 1:
               sum += arr[i];
    }

In this case, no diagnostic warning is issued.

If the 'switch' already has comments or 'fallthrough' attributes, it will trigger the diagnostic all the same because such code looks even more suspicious.

The warning is not issued when other statements interrupting execution of the 'switch' are used instead of 'break' (these are 'return', 'throw', and the like).

False positives are possible since the analyzer cannot figure out for sure if a certain fragment is an error or not. To eliminate them, use 'fallthrough' attributes or comments. Such comments will, in the first place, help other developers who will maintain the code in the future; compilers and static analyzers will also be able to recognize them.

If there are too many false positives, you can turn this diagnostic off or use one of the false positive suppression mechanisms.

This diagnostic is classified as:

CWE-484 CERT-MSC17-C

You can look at examples of errors detected by the V796 diagnostic.