View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0001205 | 1003.1(2016/18)/Issue7+TC2 | Base Definitions and Headers | public | 2018-09-02 01:44 | 2024-06-11 09:08 |
| Reporter | kre | Assigned To | |||
| Priority | normal | Severity | Objection | Type | Clarification Requested |
| Status | Closed | Resolution | Accepted As Marked | ||
| Name | Robert Elz | ||||
| Organization | |||||
| User Reference | |||||
| Section | XBD 5 | ||||
| Page Number | 124 | ||||
| Line Number | 3549 | ||||
| Interp Status | --- | ||||
| Final Accepted Text | 0001205:0004351 | ||||
| Summary | 0001205: Incorrect specification of printf %% | ||||
| Description | XBD 5 is mostly used as a method to specify formats used for output by various utilities and system interfaces (perhaps), and for that as it is it is fine, as it only needs to adequately describe the formats that are actually used in those other places, what would happen if someone did .... is not important. But it is also used by XCU 4 to specify the operation of the printf utility, and there it does matter, as users can supply any random format string. The issue is that '%' is described as a format conversion specifier (in addition to its role as the introducer of a conversion specification) The text starting at line 3439 on page 122 says: Each conversion specification is introduced by the <percent-sign> character ('%'). After the character '%', the following shall appear in sequence: flags Zero or more ... field width An optional ... precision [this one is not stated as optional, that should also be corrected ... but is not the primary subject of this issue] conversion specification characters [should be singular, only one is permitted in each conversion ... also not primary subject of this issue] And then The conversion specifiers and their meanings are: [followed by a big long list, followed, last, by, at line 3549, on page 124:] % Write a '%' character; no argument is converted. The problem is that this all suggests that %-4.3% is a legal conversion, and we all know it isn't, the '%' "conversion specification" can only occur as %% In XSH 3 (System Interfaces) the page for fprintf (page 914) at lines 30986-7 which is all (unsurprisingly) very similar, this is (kind of) handled as ... % Print a '%' character; no argument is converted. The complete conversion specification shall be %%. which is kind of adequate, but not the best solution - the issue is that %% is not a conversion specification at all, and should not be listed as one. Rather the introductory text should be something more like Each conversion specification is introduced by the <percent-sign> character ('%') followed by a character that is not another '%'. If consecutive '%' characters appear, a single '%' shall be written. Otherwise after the character '%', the following shall appear in sequence: which actually specifies what happens, rather than trying to fake the second % as a conversion specifier, but a magic one for which none of the intervening data is permitted. | ||||
| Desired Action | Change lines 3439-3440 (page 122) to: Each conversion specification is introduced by the <percent-sign> character ('%') followed by a character that is not another '%'. If consecutive '%' characters appear, a single '%' shall be written. Otherwise after the character '%', the following shall appear in sequence: In line 3447 change the first word of the paragraph ("Gives") to: Optionally gives and in lines 3451-2 (the last sentence of this same paragraph), change "The precision shall" to When given, the precision shall In line 3454 change "conversion specifier characters" to conversion specifier character Delete line 3549 (page 124). Of those the first and last changes are those relevant to the primary issue raised here, the other changes just fix the more minor irritants noticed while looking. The primary issue could also be corrected in a similar manner to that used for fprintf(3) but that is a sub-optimal solution. If consistency is desired, it would be better to also change the fprintf specification in a similar way to that proposed here. % neither is, nor ever has been, a conversion specification. | ||||
| Tags | tc3-2008 | ||||
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FWIW, ksh93 supports %flags% (ksh93 supports quite a large number of extensions when it comes to those flags), though those flags seem to be ignored for %%. All of %(whatever)%, %02%, %.0$%, %1.2.3% expand to % there. > Each conversion specification is introduced by the > <percent-sign> character ('%') followed by a character > that is not another '%'. If consecutive '%' characters > appear, a single '%' shall be written. Otherwise after > the character '%', the following shall appear in sequence: Maybe "if *two* consecutive '%' characters" as otherwise it may suggest that %%% should result in %. |
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Re note 4099 Maybe "if *two* consecutive '%' characters" Yes, agreed (that's what I was thinking...) And (edited in later) the ksh93 variant would still be allowed, of course, implementations are free to add new format conversion characters, and there's no reason that '%' cannot be one of them - as a format conversion specifier, it can take whatever flag or width args it likes, and do whatever it feels like with them (including nothing). The only requirement would be that "%%" would always output a '%' and that is the form that applications should always use (unless they explicitly want the non-portable extensions.) Or more explicitly, printf(1) should not be expected to support %4% (or anything similar). |
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Change the description of the % conversion specification in the File Format Notation section in XBD Chapter 5 on P124, L3549 from:%to:Write a '%' character; no argument is converted. %Write a '%' character; no argument is converted. Applications using the printf utility shall ensure that the complete conversion specification is %%. On page 914 line 30986 section fprintf(), change: Print a '%' character; no argument is converted. The complete conversion specification shall be %%.to: Write a '%' character; no argument is converted. The application shall ensure that the complete conversion specification is %%. On page 998 line 33951 section fwprintf(), change: Output a '%' wide character; no argument is converted. The complete conversion specification shall be %%.to: Write a '%' wide character; no argument is converted. The application shall ensure that the complete conversion specification is %%. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2018-09-02 01:44 | kre | New Issue | |
| 2018-09-02 01:44 | kre | Name | => Robert Elz |
| 2018-09-02 01:44 | kre | Section | => XBD 5 |
| 2018-09-02 01:44 | kre | Page Number | => 124 |
| 2018-09-02 01:44 | kre | Line Number | => 3549 |
| 2018-09-02 11:49 | stephane | Note Added: 0004099 | |
| 2018-09-02 17:01 | kre | Note Added: 0004100 | |
| 2018-09-02 17:06 | kre | Note Edited: 0004100 | |
| 2019-04-01 15:41 | geoffclare | Note Added: 0004351 | |
| 2019-04-01 15:43 | geoffclare | Interp Status | => --- |
| 2019-04-01 15:43 | geoffclare | Final Accepted Text | => 0001205:0004351 |
| 2019-04-01 15:43 | geoffclare | Status | New => Resolved |
| 2019-04-01 15:43 | geoffclare | Resolution | Open => Accepted As Marked |
| 2019-04-01 15:43 | geoffclare | Tag Attached: tc3-2008 | |
| 2019-11-13 10:06 | geoffclare | Status | Resolved => Applied |
| 2024-06-11 09:08 | agadmin | Status | Applied => Closed |
