View Issue Details
| ID | Project | Category | View Status | Date Submitted | Last Update |
|---|---|---|---|---|---|
| 0001633 | Issue 8 drafts | Base Definitions and Headers | public | 2023-02-16 10:07 | 2024-09-05 16:10 |
| Reporter | nrk | Assigned To | |||
| Priority | normal | Severity | Comment | Type | Enhancement Request |
| Status | New | Resolution | Open | ||
| Name | Nickolas Raymond Kaczynski | ||||
| Organization | |||||
| User Reference | |||||
| Section | <string.h> | ||||
| Page Number | n/a | ||||
| Line Number | n/a | ||||
| Final Accepted Text | |||||
| Summary | 0001633: Add memrchr | ||||
| Description | memrchr is a simple and useful function that is similar to memchr, except it finds the last occurrence of a byte. It is provided by the following implementations already: * glibc (https://www.man7.org/linux/man-pages/man3/memrchr.3.html) * musl * openbsd (https://man.openbsd.org/memrchr.3) * freebsd (https://man.freebsd.org/cgi/man.cgi?query=memrchr&manpath=FreeBSD+13.1-RELEASE+and+Ports) (And probably many others). | ||||
| Desired Action | Under section <string.h> add: void *memrchr(const void *s, int c, size_t n); Under memchr, add memrchr to SEE ALSO. Add a new memrchr page: NAME memrchr - find last occurrence of a byte in memory SYNOPSIS #include <string.h> void *memrchr(const void *s, int c, size_t n); DESCRIPTION The memrchr() function shall locate the last occurrence of c (converted to an unsigned char) in the initial n bytes (each interpreted as unsigned char) pointed to by s. RETURN VALUE The memrchr() function shall return a pointer to the located byte, or a null pointer if the byte is not found. ERRORS No errors are defined. | ||||
| Tags | No tags attached. | ||||
|
|
In addition to memchr(), the standard also includes wmemchr(). Does this request also intend to add wmemrchr()? |
|
|
The purpose of this defect report was to standardize a widely implemented interface. I've quickly looked into glibc, musl, freebsd & openbsd and none of them seem to provide wmemrchr(). As such, I have no intention of adding wmemrchr(). |
|
|
Note 6186 was discussed in the 2023-03-06 teleconference and it was noted that because wcsrchr() is already present, it functionally serves as an equivalent for most situations to wmemrchr(), and this is a reason there hasn't been much call to implement wmemrchr(). However, for searching blocks that may have embedded wide null chars it is not sufficient; application code is necessary to find the last null before attempting the right scan. As such, for symmetry and completeness the consensus is more the standard should contain the interface, unless some implementation has a compelling reason it can communicate here why it shouldn't be. |
|
|
Discussed on the 2024-08-22 call: At this point, we are unaware of any wmemrchr() implementations. While searching backwards for a byte can be done efficiently, searching backwards for the start of a multibyte character can be difficult depending on the encoding, at which point a loop over searching forward until reaching the end of the memory is just as efficient without needing a new specialized function. The consensus for now is that the Austin Group is willing to sponsor memrchr() with a rationale stating why there is no wmemrchr(), which could be amended at a later date if a wmemrchr() is no longer invention. |
|
|
Regarding 0001633:0006867 - I have been reminded that wmemrchr() is about searching wchar_t not multibyte characters (searching backwards on multibyte characters is not trivial, but searching wchar_t can be efficient); but the point remains that the Austin Group is unaware of any implementations of wmemrchr() or applications that would benefit from having it. |
| Date Modified | Username | Field | Change |
|---|---|---|---|
| 2023-02-16 10:07 | nrk | New Issue | |
| 2023-02-16 10:07 | nrk | Name | => Nickolas Raymond Kaczynski |
| 2023-02-16 10:07 | nrk | Section | => <string.h> |
| 2023-02-16 10:07 | nrk | Page Number | => n/a |
| 2023-02-16 10:07 | nrk | Line Number | => n/a |
| 2023-03-02 16:56 | Don Cragun | Note Added: 0006185 | |
| 2023-03-02 17:10 | nrk | Note Added: 0006186 | |
| 2023-03-06 16:36 | shware_systems | Note Added: 0006194 | |
| 2024-08-22 15:24 | eblake | Note Added: 0006867 | |
| 2024-09-05 16:10 | eblake | Note Added: 0006875 |
