STRCPY(3)

STRCPY(3) | Library Functions Manual | STRCPY(3)

# NAME

stpcpy, stpncpy, strcpy, strncpy — copy strings

# LIBRARY

Standard C Library (libc, -lc)

# SYNOPSIS

#include <string.h>

char *
stpcpy(char * restrict dst, const char * restrict src);

char *
stpncpy(char * restrict dst, const char * restrict src, size_t len);

char *
strcpy(char * restrict dst, const char * restrict src);

char *
strncpy(char * restrict dst, const char * restrict src, size_t len);

# DESCRIPTION

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.

# 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[len]` (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 parameter. strncpy() only NUL-terminates the destination string when the length of the source string is less than the length parameter.

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 and more simply 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.

# SEE ALSO

bcopy(3), memccpy(3), memcpy(3), memmove(3), strlcpy(3), wcscpy(3)

# STANDARDS

The strcpy() and strncpy() functions conform to ISO/IEC 9899:1999 (“ISO C99”). The stpcpy() and stpncpy() functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

# HISTORY

The stpcpy() and stpncpy() functions first appeared in NetBSD 6.0.

# SECURITY CONSIDERATIONS

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

May 1, 2009 | NetBSD 7.1