strlcpy(3) — Linux manual page

strlcpy(3)               Library Functions Manual              strlcpy(3)

NAME         top

       strlcpy, strlcat - string return-hypothetical-non-truncated-length
       copy/catenate (with truncation)

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <string.h>

       size_t strlcpy(size_t dsize;
                      char dst[restrict dsize], const char *restrict src,
                      size_t dsize);
       size_t strlcat(size_t dsize;
                      char dst[restrict dsize], const char *restrict src,
                      size_t dsize);

DESCRIPTION         top

       strlcpy() copies the string pointed to by src, into a string at
       the buffer pointed to by dst.

       strlcat() catenates the string pointed to by src, after the string
       pointed to by dst (overwriting its terminating null byte).

       For both functions, if the string doesn't fit in the buffer, it is
       truncated.

RETURN VALUE         top

       These functions return the total length of the string they tried
       to create, as if truncation didn't happen.

STANDARDS         top

       POSIX.1-2024.

HISTORY         top

       OpenBSD 2.4, POSIX.1-2024, glibc 2.38.

BUGS         top

       These functions are vulnerable to denial of service (DoS) attacks,
       since they read the entire source string.

       strscpy(9) is a better function for copying with truncation, as it
       doesn't have that issue.  It's not provided by libc, so users
       should write their own implementation.

SEE ALSO         top

       strlcpy(3), strcpy(3), string(3)

COLOPHON         top

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Linux man-pages 6.19            2026-07-11                     strlcpy(3)

Pages that refer to this page: strlcpy(3),  string_copying(7)

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