From Jason Turner

[dcl.attr.fallthrough]

C++17 → C++20 3.0 KB 42 lines
Current Draft | LaTeX Source
Archived: C++17 | C++20
Markdown: C++17 | C++20
Explore in Adventure Game

Diff to HTML by rtfpessoa

Files changed (1) hide show
  1. tmp/tmphgd_jz32/{from.md → to.md} +26 -12
tmp/tmphgd_jz32/{from.md → to.md} RENAMED
@@ -1,23 +1,25 @@
1
  ### Fallthrough attribute <a id="dcl.attr.fallthrough">[[dcl.attr.fallthrough]]</a>
2
 
3
- The *attribute-token* `fallthrough` may be applied to a null statement (
4
- [[stmt.expr]]); such a statement is a fallthrough statement. The
5
  *attribute-token* `fallthrough` shall appear at most once in each
6
  *attribute-list* and no *attribute-argument-clause* shall be present. A
7
  fallthrough statement may only appear within an enclosing `switch`
8
- statement ([[stmt.switch]]). The next statement that would be executed
9
  after a fallthrough statement shall be a labeled statement whose label
10
- is a case label or default label for the same `switch` statement. The
11
- program is ill-formed if there is no such statement.
 
 
 
12
 
13
- [*Note 1*: The use of a fallthrough statement is intended to suppress a
14
- warning that an implementation might otherwise issue for a case or
15
- default label that is reachable from another case or default label along
16
- some path of execution. Implementations are encouraged to issue a
17
- warning if a fallthrough statement is not dynamically
18
- reachable. — *end note*]
19
 
20
  [*Example 1*:
21
 
22
  ``` cpp
23
  void f(int n) {
@@ -26,14 +28,26 @@ void f(int n) {
26
  case 1:
27
  case 2:
28
  g();
29
  [[fallthrough]];
30
  case 3: // warning on fallthrough discouraged
 
 
 
 
 
 
 
 
 
 
 
 
31
  h();
32
  case 4: // implementation may warn on fallthrough
33
  i();
34
- [[fallthrough]]; // ill-formed
35
  }
36
  }
37
  ```
38
 
39
  — *end example*]
 
1
  ### Fallthrough attribute <a id="dcl.attr.fallthrough">[[dcl.attr.fallthrough]]</a>
2
 
3
+ The *attribute-token* `fallthrough` may be applied to a null statement
4
+ [[stmt.expr]]; such a statement is a fallthrough statement. The
5
  *attribute-token* `fallthrough` shall appear at most once in each
6
  *attribute-list* and no *attribute-argument-clause* shall be present. A
7
  fallthrough statement may only appear within an enclosing `switch`
8
+ statement [[stmt.switch]]. The next statement that would be executed
9
  after a fallthrough statement shall be a labeled statement whose label
10
+ is a case label or default label for the same `switch` statement and, if
11
+ the fallthrough statement is contained in an iteration statement, the
12
+ next statement shall be part of the same execution of the substatement
13
+ of the innermost enclosing iteration statement. The program is
14
+ ill-formed if there is no such statement.
15
 
16
+ *Recommended practice:* The use of a fallthrough statement should
17
+ suppress a warning that an implementation might otherwise issue for a
18
+ case or default label that is reachable from another case or default
19
+ label along some path of execution. Implementations should issue a
20
+ warning if a fallthrough statement is not dynamically reachable.
 
21
 
22
  [*Example 1*:
23
 
24
  ``` cpp
25
  void f(int n) {
 
28
  case 1:
29
  case 2:
30
  g();
31
  [[fallthrough]];
32
  case 3: // warning on fallthrough discouraged
33
+ do {
34
+ [[fallthrough]]; // error: next statement is not part of the same substatement execution
35
+ } while (false);
36
+ case 6:
37
+ do {
38
+ [[fallthrough]]; // error: next statement is not part of the same substatement execution
39
+ } while (n--);
40
+ case 7:
41
+ while (false) {
42
+ [[fallthrough]]; // error: next statement is not part of the same substatement execution
43
+ }
44
+ case 5:
45
  h();
46
  case 4: // implementation may warn on fallthrough
47
  i();
48
+ [[fallthrough]]; // error
49
  }
50
  }
51
  ```
52
 
53
  — *end example*]