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Diffstat (limited to 'man3/strcpy.3')
| -rw-r--r-- | man3/strcpy.3 | 74 |
1 files changed, 61 insertions, 13 deletions
diff --git a/man3/strcpy.3 b/man3/strcpy.3 index 38afa973..aa8c9a3d 100644 --- a/man3/strcpy.3 +++ b/man3/strcpy.3 @@ -27,8 +27,10 @@ .\" Modified Sat Jul 24 18:06:49 1993 by Rik Faith (faith@cs.unc.edu) .\" Modified Fri Aug 25 23:17:51 1995 by Andries Brouwer (aeb@cwi.nl) .\" Modified Wed Dec 18 00:47:18 1996 by Andries Brouwer (aeb@cwi.nl) +.\" 2007-06-15, Marc Boyer <marc.boyer@enseeiht.fr> + mtk +.\" Improve discussion of strncpy(). .\" -.TH STRCPY 3 1993-04-11 "GNU" "Linux Programmer's Manual" +.TH STRCPY 3 2007-06-15 "GNU" "Linux Programmer's Manual" .SH NAME strcpy, strncpy \- copy a string .SH SYNOPSIS @@ -42,27 +44,49 @@ strcpy, strncpy \- copy a string .SH DESCRIPTION The .BR strcpy () -function copies the string pointed to by \fIsrc\fP -(including the terminating `\\0' character) to the array pointed to by -\fIdest\fP. +function copies the string pointed to by \fIsrc\fP, +including the terminating null byte ('\\0'), +to the buffer pointed to by \fIdest\fP. The strings may not overlap, and the destination string \fIdest\fP must be large enough to receive the copy. .PP The .BR strncpy () -function is similar, except that not more than +function is similar, except that at most \fIn\fP bytes of \fIsrc\fP are copied. -Thus, if there is no null byte -among the first \fIn\fP bytes of \fIsrc\fP, the result will not be -null-terminated. +.BR Warning : +If there is no null byte +among the first \fIn\fP bytes of \fIsrc\fP, +the string placed in \fIdest\fP will not be null terminated. .PP -In the case where the length of +If the length of .I src -is less than that of +is less than .IR n , -the remainder of +.BR strncat () +pads the remainder of .I dest -will be padded with null bytes. +with null bytes. +.PP +A simple implementation of +.BR strncpy () +might be: +.in +0.25i +.nf + +char* +strncpy(char *dest, const char *src, size_t n){ + size_t i; + + for(i = 0 ; i < n && src[i] != '\\0' ; i++) + dest[i] = src[i]; + for( ; i < n ; i++) + dest[i] = '\\0'; + + return dest; +} +.fi +.in .SH "RETURN VALUE" The .BR strcpy () @@ -72,11 +96,35 @@ functions return a pointer to the destination string \fIdest\fP. .SH "CONFORMING TO" SVr4, 4.3BSD, C89, C99. +.SH NOTES +Some programmers consider +.BR strncpy () +to be inefficient and error prone. +If the programmer knows (i.e., includes code to test!) +that the size of \fIdest\fP is greater than +the length of \fIsrc\fP, then +.BR strcpy () +can be used. + +If there is no terminating null byte in the first \fIn\fP +characters of \fIsrc\fP, +.BR strncpy () +produces an unterminated string in \fIdest\fP. +Programmers often prevent this mistake by forcing termination +as follows: +.in +0.25i +.nf + +strncpy(buf, str, n); +if (n > 0) + buf[n - 1]= '\0'; +.fi +.in .SH BUGS If the destination string of a .BR strcpy () is not large enough -(that is, if the programmer was stupid/lazy, and failed to check +(that is, if the programmer was stupid or lazy, and failed to check the size before copying) then anything might happen. Overflowing fixed length strings is a favourite cracker technique. .SH "SEE ALSO" |