strcpy3

Usage

Library

Standard C Library (libc, -lc)

Admonishment

YOU SHOULD ALMOST CERTAINLY USE strlcpy() INSTEAD.

See "Examples" below.

Overview

The stpcpy() and strcpy() functions copy the string src to dst (including the terminating ‘\0’ character.)

The stpncpy() and strncpy() functions copy at most len characters from src into dst. If src is less than len characters long, the remainder of dst is filled with ‘\0’ characters. Otherwise, dst is not terminated.

The source and destination strings should not overlap, as the behavior is undefined.

Return values

The strcpy() and strncpy() functions return dst. The stpcpy() and stpncpy() functions return a pointer to the terminating ‘\0’ character of dst. If stpncpy() does not terminate dst with a NUL character, it instead returns a pointer to dst[n] (which does not necessarily refer to a valid memory location.)

Examples

The following sets chararray to “abc\0\0\0”:

char chararray[6];
(void)strncpy(chararray, "abc", sizeof(chararray));

The following sets chararray to “abcdef”:

char chararray[6];
(void)strncpy(chararray, "abcdefgh", sizeof(chararray));

Note that it does not NUL terminate chararray because the length of the source string is greater than or equal to the length argument.

The following copies as many characters from input to buf as will fit and NUL terminates the result. Because strncpy() does not guarantee to NUL terminate the string itself, this must be done explicitly.

char buf[1024];
(void)strncpy(buf, input, sizeof(buf) - 1);
buf[sizeof(buf) - 1] = '\0';

This could be better achieved using strlcpy(3), as shown in the following example:

(void)strlcpy(buf, input, sizeof(buf));

Note that because strlcpy(3) is not defined in any standards, it should only be used when portability is not a concern.

Security considerations

The strcpy() function is easily misused in a manner which enables malicious users to arbitrarily change a running program's functionality through a buffer overflow attack.