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| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2012-07-19 11:29:15 +0200 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2012-07-20 12:52:45 +0200 |
| commit | bb96fc35a3b664ef3959eaefb095608846f89df7 (patch) | |
| tree | 56422bc1d40b6de03d0eac055bf05098f6c2db40 /man3/strcpy.3 | |
| parent | 276d73b6ed8357c28473d812fa18a6622f841a78 (diff) | |
| download | man-pages-bb96fc35a3b664ef3959eaefb095608846f89df7.tar.gz | |
strcpy.3: NOTES: Add a discussion of strlcpy()
Inspired by https://lwn.net/Articles/506530/
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man3/strcpy.3')
| -rw-r--r-- | man3/strcpy.3 | 50 |
1 files changed, 49 insertions, 1 deletions
diff --git a/man3/strcpy.3 b/man3/strcpy.3 index 260bd853b7..afc751e3b9 100644 --- a/man3/strcpy.3 +++ b/man3/strcpy.3 @@ -30,7 +30,7 @@ .\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk .\" Improve discussion of strncpy(). .\" -.TH STRCPY 3 2012-07-18 "GNU" "Linux Programmer's Manual" +.TH STRCPY 3 2012-07-19 "GNU" "Linux Programmer's Manual" .SH NAME strcpy, strncpy \- copy a string .SH SYNOPSIS @@ -111,6 +111,15 @@ the length of \fIsrc\fP, then .BR strcpy () can be used. +One valid (and intended) use of +.BR strncpy () +is to copy a C string to a fixed-length buffer +while ensuring both that the buffer is not overflowed +and that unused bytes in the target buffer are zeroed out +(perhaps to prevent information leaks if the buffer is to +written to media or transmitted to another process via an +interprocess communication technique). + If there is no terminating null byte in the first \fIn\fP bytes of \fIsrc\fP, .BR strncpy () @@ -131,6 +140,45 @@ information contained in .I src is lost in the copying to .IR dest .) + +Some systems (the BSDs, Solaris, and others) provide the following function: + + size_t strlcpy(char *dest, const char *src, size_t size); + +.\" http://static.usenix.org/event/usenix99/full_papers/millert/millert_html/index.html +.\" "strlcpy and strlcat - consistent, safe, string copy and concatenation" +.\" 1999 USENIX Annual Technical Conference +This function is similar to +.BR strncpy (), +but it copies at most +.I size\-1 +bytes to +.IR dest , +always adds a terminating null byte, +and does not pad the target with (further) null bytes. +This function fixes some of the problems of +.BR strcpy () +and +.BR strncpy (), +but the caller must still handle the possibility of data loss if +.I size +is too small. +The return value of the function is the length of +.IR src , +which allows truncation to be easily detected: +if the return value is greater than or equal to +.IR size , +truncation occurred. +If loss of data matters, the caller +.I must +either check the arguments before the call, +or test the function return value. +.BR strlcpy () +is not present in glibc and is not standardized by POSIX, +.\" https://lwn.net/Articles/506530/ +but is available on Linux via the +.IR libbsd +library. .SH BUGS If the destination string of a .BR strcpy () |