atoul.3

This a good VPN source

.TH IPSEC_ATOUL 3 "11 June 2001"
.\" RCSID $Id: atoul.3,v 1.10 2004/04/09 18:00:39 mcr Exp $
.SH NAME
ipsec atoul, ultoa \- convert unsigned-long numbers to and from ASCII
.SH SYNOPSIS
.B "#include <freeswan.h>
.sp
.B "const char *atoul(const char *src, size_t srclen,"
.ti +1c
.B "int base, unsigned long *n);"
.br
.B "size_t ultoa(unsigned long n, int base, char *dst,"
.ti +1c
.B "size_t dstlen);"
.SH DESCRIPTION
These functions are obsolete; see
.IR ipsec_ttoul (3)
for their replacements.
.PP
.I Atoul
converts an ASCII number into a binary
.B "unsigned long"
value.
.I Ultoa
does the reverse conversion, back to an ASCII version.
.PP
Numbers are specified in ASCII as
decimal (e.g.
.BR 123 ),
octal with a leading zero (e.g.
.BR 012 ,
which has value 10),
or hexadecimal with a leading
.B 0x
(e.g.
.BR 0x1f ,
which has value 31)
in either upper or lower case.
.PP
The
.I srclen
parameter of
.I atoul
specifies the length of the ASCII string pointed to by
.IR src ;
it is an error for there to be anything else
(e.g., a terminating NUL) within that length.
As a convenience for cases where an entire NUL-terminated string is
to be converted,
a
.I srclen
value of
.B 0
is taken to mean
.BR strlen(src) .
.PP
The
.I base
parameter of
.I atoul
can be
.BR 8 ,
.BR 10 ,
or
.BR 16 ,
in which case the number supplied is assumed to be of that form
(and in the case of
.BR 16 ,
to lack any
.B 0x
prefix).
It can also be
.BR 0 ,
in which case the number is examined for a leading zero
or a leading
.B 0x
to determine its base,
or
.B 13
(halfway between 10 and 16),
which has the same effect as
.B 0
except that a non-hexadecimal
number is considered decimal regardless of any leading zero.
.PP
The
.I dstlen
parameter of
.I ultoa
specifies the size of the
.I dst
parameter;
under no circumstances are more than
.I dstlen
bytes written to
.IR dst .
A result which will not fit is truncated.
.I Dstlen
can be zero, in which case
.I dst
need not be valid and no result is written,
but the return value is unaffected;
in all other cases, the (possibly truncated) result is NUL-terminated.
.PP
The
.I base
parameter of
.I ultoa
must be
.BR 8 ,
.BR 10 ,
or
.BR 16 .
.PP
.I Atoul
returns NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
.I Ultoa
returns the size of buffer which would 
be needed to
accommodate the full conversion result, including terminating NUL;
it is the caller's responsibility to check this against the size of
the provided buffer to determine whether truncation has occurred.
.SH SEE ALSO
atol(3), strtoul(3)
.SH DIAGNOSTICS
Fatal errors in
.I atoul
are:
empty input;
unknown
.IR base ;
non-digit character found;
number too large for an
.BR "unsigned long" .
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
There is no provision for reporting an invalid
.I base
parameter given to
.IR ultoa .
.PP
The restriction of error reports to literal strings
(so that callers don't need to worry about freeing them or copying them)
does limit the precision of error reporting.
.PP
The error-reporting convention lends itself to slightly obscure code,
because many readers will not think of NULL as signifying success.
A good way to make it clearer is to write something like:
.PP
.RS
.nf
.B "const char *error;"
.sp
.B "error = atoul( /* ... */ );"
.B "if (error != NULL) {"
.B "        /* something went wrong */"
.fi
.RE