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STRTOU(3) NetBSD Library Functions Manual STRTOU(3)
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strtou -- convert a string to an uintmax_t integer
Standard C Library (libc, -lc)
strtou(const char * restrict nptr, char ** restrict endptr, int base,
uintmax_t lo, uintmax_t hi, int *rstatus);
The strtou() function converts the string in nptr to an uintmax_t value.
The strtou() function uses internally strtoumax(3) and ensures that the
result is always in the range [ lo .. hi ]. In adddition it always
places 0 on success or a conversion status in the rstatus argument,
avoiding the errno gymnastics the other functions require. The rstatus
argument can be NULL if conversion status is to be ignored.
The string may begin with an arbitrary amount of white space (as deter-
mined by isspace(3)) followed by a single optional `+' or `-' sign. If
base is zero or 16, the string may then include a `0x' or `0X' prefix,
and the number will be read in base 16; otherwise, a zero base is taken
as 10 (decimal) unless the next character is `0', in which case it is
taken as 8 (octal).
The remainder of the string is converted to an uintmax_t value in the
obvious manner, stopping at the end of the string or at the first charac-
ter that does not produce a valid digit in the given base. (In bases
above 10, the letter `A' in either upper or lower case represents 10, `B'
represents 11, and so forth, with `Z' representing 35.)
If endptr is non-nil, strtou() stores the address of the first invalid
character in *endptr. If there were no digits at all, however, strtou()
stores the original value of nptr in *endptr. (Thus, if *nptr is not
`\0' but **endptr is `\0' on return, the entire string was valid.)
The strtou() function always returns the closest value in the range spec-
ified by the lo and hi arguments.
The errno value is guaranteed to be left unchanged.
Errors are stored as the conversion status in the rstatus argument.
The following example will always return a number in [1..99] range no
matter what the input is, and warn if the conversion failed.
uintmax_t lval = strtou(buf, NULL, 0, 1, 99, &e);
warnc(e, "conversion of `%s' to a number failed, using %ju",
[ECANCELED] The string did not contain any characters that were
[EINVAL] The base is not between 2 and 36 and does not contain
the special value 0.
[ENOTSUP] The string contained non-numeric characters that did
not get converted. In this case, endptr points to the
first unconverted character.
[ERANGE] The given string was out of range; the value converted
has been clamped; or the range given was invalid, i.e.
lo > hi.
atof(3), atoi(3), atol(3), atoll(3), strtod(3), strtoi(3), strtoimax(3),
strtol(3), strtoll(3), strtoul(3), strtoull(3), strtoumax(3)
The strtou() function is a NetBSD extension.
The strtou() function first appeared in NetBSD 7. OpenBSD introduced the
strtonum(3) function for the same purpose, but the interface makes it
impossible to properly differentiate illegal returns.
Ignores the current locale.
NetBSD 9.1 November 13, 2015 NetBSD 9.1