ggstrlcpy(3) GGI ggstrlcpy(3)NAME
ggstrlcpy, ggstrlcat : size-bounded string copying and concatenation
SYNOPSIS
#include <ggi/gg.h>
size_t ggstrlcpy(char *dst, const char *src, size_t siz);
size_t ggstrlcat(char *dst, const char *src, size_t siz);
DESCRIPTION
The ggstrlcpy and ggstrlcat functions copy and concatenate strings
respectively. They are designed to be safer, more consistent, and less
error prone replacements for strncpy(3) and strncat(3). Unlike those
functions, ggstrlcpy and ggstrlcat take the full size of the buffer
(not just the length) and guarantee to NUL-terminate the result (as
long as size is larger than 0 or, in the case of ggstrlcat, as long as
there is at least one byte free in dst). Note that you should include
a byte for the NUL in size. Also note that ggstrlcpy and ggstrlcat
only operate on true C strings. This means that for ggstrlcpy src must
be NUL-terminated and for ggstrlcat both src and dst must be NUL-termi‐
nated.
The ggstrlcpy function copies up to siz - 1 characters from the NUL-
terminated string src to dst, NUL-terminating the result.
The ggstrlcat function appends the NUL-terminated string src to the end
of dst. It will append at most siz - strlen(dst) - 1 bytes, NUL-termi‐
nating the result.
RETURN VALUES
The ggstrlcpy and ggstrlcat functions return the total length of the
string they tried to create. For ggstrlcpy that means the length of
src. For ggstrlcat that means the initial length of dst plus the
length of src. While this may seem somewhat confusing it was done to
make truncation detection simple.
Note however, that if ggstrlcat traverses size characters without find‐
ing a NUL, the length of the string is considered to be size and the
destination string will not be NUL-terminated (since there was no space
for the NUL). This keeps ggstrlcat from running off the end of a
string. In practice this should not happen (as it means that either
size is incorrect or that dst is not a proper C string). The check
exists to prevent potential security problems in incorrect code.
EXAMPLES
The following code fragment illustrates the simple case:
char *s, *p, buf[BUFSIZ];
(void)ggstrlcpy(buf, s, sizeof(buf));
(void)ggstrlcat(buf, p, sizeof(buf));
To detect truncation, perhaps while building a pathname, something like
the following might be used:
char *dir, *file, pname[MAXPATHLEN];
if (ggstrlcpy(pname, dir, sizeof(pname)) >= sizeof(pname))
goto toolong;
if (ggstrlcat(pname, file, sizeof(pname)) >= sizeof(pname))
goto toolong;
Since we know how many characters we copied the first time, we can
speed things up a bit by using a copy instead of an append:
char *dir, *file, pname[MAXPATHLEN];
size_t n;
n = ggstrlcpy(pname, dir, sizeof(pname));
if (n >= sizeof(pname))
goto toolong;
if (ggstrlcpy(pname + n, file, sizeof(pname) - n) >= sizeof(pname) - n)
goto toolong;
However, one may question the validity of such optimizations, as they
defeat the whole purpose of ggstrlcpy and ggstrlcat.
SEE ALSOsnprintf(3)strncat(3)strncpy(3)HISTORY
strlcpy and strlcat first appeared in OpenBSD 2.4, then in NetBSD 1.4.3
and FreeBSD 3.3.0. ggstrlcpy and ggstrlcat has been added to libgg for
portability.
libgg-1.0.x 2005-08-26 ggstrlcpy(3)
