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| ID | Category | Severity | Type | Date Submitted | Last Update | ||
| 0000701 | [1003.1(2013)/Issue7+TC1] System Interfaces | Objection | Error | 2013-05-20 11:20 | 2024-06-11 09:02 | ||
| Reporter | geoffclare | View Status | public | ||||
| Assigned To | |||||||
| Priority | normal | Resolution | Accepted As Marked | ||||
| Status | Closed | ||||||
| Name | Geoff Clare | ||||||
| Organization | The Open Group | ||||||
| User Reference | |||||||
| Section | ungetc(), ungetwc() | ||||||
| Page Number | 2170, 2172 | ||||||
| Line Number | 69084, 69130 | ||||||
| Interp Status | --- | ||||||
| Final Accepted Text | See Note: 0004546. | ||||||
| Summary | 0000701: unget[w]c() and file position after discarding push back | ||||||
| Description |
The ungetc() description, as updated by TC1, includes the following: The value of the file-position indicator for the stream after all pushed-back bytes have been read, or discarded by calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be the same as it was before the bytes were pushed back. Similarly for ungetwc() (with "characters" instead of "bytes"). The "discarded" part of this requirement does not make any sense. All of the listed functions which discard the push back also _set_ the file position. The file position will end up as whatever the function sets it to, not "the same as it was before the bytes [or characters] were pushed back". Since these requirements derive from the C Standard, we should raise this issue with the C committee. |
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| Desired Action |
For ungetc() change: The value of the file-position indicator for the stream after all pushed-back bytes have been read, or discarded by calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be the same as it was before the bytes were pushed back. to: The value of the file-position indicator for the stream after all pushed-back bytes have been read shall be the same as it was before the bytes were pushed back. For ungetwc() change: The value of the file-position indicator for the stream after all pushed-back characters have been read, or discarded by calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be the same as it was before the characters were pushed back. to: The value of the file-position indicator for the stream after all pushed-back characters have been read shall be the same as it was before the characters were pushed back. Also add something to the RATIONALE sections for these two functions, pointing out that some text from the C Standard intentionally does not appear in POSIX. The wording will depend on the response we get from the C committee. |
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| Tags | c99, tc3-2008 | ||||||
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Notes |
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(0002218) nick (manager) 2014-04-10 14:54 |
Under consideration by C. See: http://open-std.org/JTC1/SC22/WG14/www/docs/n1720.htm [^] This was discussed at the Chicago C meeting in 2013: ungetc / ungetwc and file position after discarding push back problems. Ref Austin Group Defect #701, says that “or discarding” makes no sense. Larry Jones pointed out that the Standard is correct as written because the intent is that the specified file position indicator is an intermediate state inside the file positioning function after the pushed‐back characters are discarded but before the actual seek. That gives you a reliable file position from which to do the seek. It’s not intended that the file positioning function doesn’t set the file position indicator. Needs a Committee Response rather than a Suggested Change –or‐ possible footnote to explain why. Bill Seymour proposed the following Suggested TC. Add a footnote after “pushed‐back characters” in the second sentence of 7.21.7.10p5: After the file positioning function discards the characters but before it actually does the repositioning. Add a footnote after “pushed‐back wide characters” in the second sentence of 7.29.3.10p5: After the file positioning function discards the characters but before it actually does the repositioning. After some discussion, we decided that the above words needed some editing. ACTION: Larry Jones to reword the Suggested TC footnote for DR 438. Leave OPEN |
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(0003373) nick (manager) 2016-09-02 15:29 |
Checking through the C committee DRs, I noticed that this one has in fact been closed for a while. The final disposition is:
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(0004546) geoffclare (manager) 2019-08-30 09:26 |
Proposed changes (implementing the direction agreed in 2019-08-29 meeting) ... On page 2193 line 70128 section ungetc(), change: A successful call to ungetc() shall clear the end-of-file indicator for the stream. The value of the file-position indicator for the stream after all pushed-back bytes have been read, or discarded by calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be the same as it was before the bytes were pushed back. The file-position indicator is decremented by each successful call to ungetc(); if its value was 0 before a call, its value is unspecified after the call.to: A successful call to ungetc() shall clear the end-of-file indicator for the stream. The file-position indicator for the stream shall be decremented by each successful call to ungetc(); if its value was 0 before a call, its value is unspecified after the call. The value of the file-position indicator after all pushed-back bytes have been read shall be the same as it was before the bytes were pushed back. On page 2193 line 70143 section ungetc(), change RATIONALE from "None" to: The C standard includes the text "The value of the file position indicator for the stream after reading or discarding all pushed-back characters shall be the same as it was before the characters were pushed back." POSIX.1 omits "or discarding" from this because it is redundant - in the C standard the discarding is done by file positioning functions and does not affect the position set by those functions. In particular, a relative seek using fseek() or fseeko() with SEEK_CUR adjusts the position relative to the position on entry to the function, not the position after the pushed-back bytes have been discarded. POSIX.1 also requires fflush() to discard pushed back bytes in situations where the C standard says the behavior of fflush() is undefined. On page 2195 line 70175 section ungetwc(), change: A successful call to ungetwc() shall clear the end-of-file indicator for the stream. The value of the file-position indicator for the stream after all pushed-back characters have been read, or discarded by calling fseek(), fseeko(), fsetpos(), or rewind() (but not fflush()), shall be the same as it was before the characters were pushed back. The file-position indicator is decremented (by one or more) by each successful call to ungetwc(); if its value was 0 before a call, its value is unspecified after the call.to: A successful call to ungetwc() shall clear the end-of-file indicator for the stream. The file-position indicator for the stream shall be decremented (by one or more) by each successful call to ungetwc(); if its value was 0 before a call, its value is unspecified after the call. The value of the file-position indicator after all pushed-back characters have been read shall be the same as it was before the characters were pushed back. On page 2195 line 70193 section ungetwc(), change RATIONALE from "None" to: The C standard includes the text "The value of the file position indicator for the stream after reading or discarding all pushed-back wide characters shall be the same as it was before the wide characters were pushed back." POSIX.1 omits "or discarding" from this because it is redundant - in the C standard the discarding is done by file positioning functions and does not affect the position set by those functions. In particular, a relative seek using fseek() or fseeko() with SEEK_CUR adjusts the position relative to the position on entry to the function, not the position after the pushed-back wide characters have been discarded. POSIX.1 also requires fflush() to discard pushed back wide characters in situations where the C standard says the behavior of fflush() is undefined. |
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Issue History |
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| Date Modified | Username | Field | Change |
| 2013-05-20 11:20 | geoffclare | New Issue | |
| 2013-05-20 11:20 | geoffclare | Name | => Geoff Clare |
| 2013-05-20 11:20 | geoffclare | Organization | => The Open Group |
| 2013-05-20 11:20 | geoffclare | Section | => ungetc(), ungetwc() |
| 2013-05-20 11:20 | geoffclare | Page Number | => 2170, 2172 |
| 2013-05-20 11:20 | geoffclare | Line Number | => 69084, 69130 |
| 2013-05-20 11:20 | geoffclare | Interp Status | => --- |
| 2013-05-20 11:20 | geoffclare | Tag Attached: c99 | |
| 2014-04-10 14:54 | nick | Note Added: 0002218 | |
| 2016-09-02 15:29 | nick | Note Added: 0003373 | |
| 2019-08-29 16:09 | eblake | Relationship added | related to 0000816 |
| 2019-08-29 16:21 | eblake | Relationship added | related to 0000087 |
| 2019-08-30 09:26 | geoffclare | Note Added: 0004546 | |
| 2019-09-05 16:08 | Don Cragun | Final Accepted Text | => See Note: 0004546. |
| 2019-09-05 16:08 | Don Cragun | Status | New => Resolved |
| 2019-09-05 16:08 | Don Cragun | Resolution | Open => Accepted As Marked |
| 2019-09-05 16:08 | Don Cragun | Tag Attached: tc3-2008 | |
| 2019-11-28 12:04 | geoffclare | Status | Resolved => Applied |
| 2020-07-15 09:30 | geoffclare | Relationship added | related to 0001374 |
| 2024-06-11 09:02 | agadmin | Status | Applied => Closed |
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