ipsec_ttoul (3) - Linux Manuals

ipsec_ttoul: convert unsigned-long numbers to and from text


ipsec_ttoul, ipsec_ultot - convert unsigned-long numbers to and from text


#include <freeswan.h>
const char *ttoul(const char src, size_t srclen, int base, unsigned long n);

size_t ultot(unsigned long n, int format, char dst, size_t dstlen);



converts a text-string number into a binary unsigned long value. Ultot does the reverse conversion, back to a text version.

Numbers are specified in text as decimal (e.g. 123), octal with a leading zero (e.g. 012, which has value 10), or hexadecimal with a leading 0x (e.g. 0x1f, which has value 31) in either upper or lower case.

The srclen parameter of ttoul specifies the length of the string pointed to by 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 srclen value of 0 is taken to mean strlen(src).

The base parameter of ttoul can be 8, 10, or 16, in which case the number supplied is assumed to be of that form (and in the case of 16, to lack any 0x prefix). It can also be 0, in which case the number is examined for a leading zero or a leading 0x to determine its base.

The dstlen parameter of ultot specifies the size of the dst parameter; under no circumstances are more than dstlen bytes written to dst. A result which will not fit is truncated. Dstlen can be zero, in which case 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. The freeswan.h header file defines a constant, ULTOT_BUF, which is the size of a buffer just large enough for worst-case results.

The format parameter of ultot must be one of:


octal conversion with leading 0


octal conversion with no leading 0


decimal conversion


same as d


hexadecimal conversion, including leading 0x


hexadecimal conversion with no leading 0x


like 16 except padded on left with 0s to eight digits (full width of a 32-bit number)

Ttoul returns NULL for success and a pointer to a string-literal error message for failure; see DIAGNOSTICS. Ultot returns 0 for a failure, and otherwise 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).


Fatal errors in ttoul are: empty input; unknown base; non-digit character found; number too large for an unsigned long.

Fatal errors in ultot are: unknown format.


Written for the FreeS/WAN project by Henry Spencer.


Conversion of 0 with format o yields 00.

Ultot format 17 is a bit of a kludge.

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.

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:

const char *error;

error = ttoul( /* ... */ );
if (error != NULL) {
        /* something went wrong */


atol(3), strtoul(3)