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from: @(#)strtoul.3 8.1 (Berkeley) 6/4/93
.Dd December 27, 2014 .Dt STRTOUL 3 .Os .Sh NAME .Nm strtou , .Nm strtoul , .Nm strtoull , .Nm strtoumax , .Nm strtouq .Nd convert a string to an unsigned long, unsigned long long, uintmax_t or uquad_t integer .Sh LIBRARY .Lb libc .Sh SYNOPSIS n stdlib.h n limits.h .Ft unsigned long int .Fn strtoul "const char * restrict nptr" "char ** restrict endptr" "int base" .Ft unsigned long long int .Fn strtoull "const char * restrict nptr" "char ** restrict endptr" "int base"
p n inttypes.h .Ft uintmax_t .Fn strtou "const char * restrict nptr" "char ** restrict endptr" "int base" "uintmax_t lo" "uintmax_t hi" "int *rstatus" .Ft uintmax_t .Fn strtoumax "const char * restrict nptr" "char ** restrict endptr" "int base"
p n sys/types.h n stdlib.h n limits.h .Ft u_quad_t .Fn strtouq "const char * restrict nptr" "char ** restrict endptr" "int base" .Sh DESCRIPTION The .Fn strtoul function converts the string in .Fa nptr to an .Ft unsigned long int value. The .Fn strtoull function converts the string in .Fa nptr to an .Ft unsigned long long int value. The .Fn strtoumax function converts the string in .Fa nptr to an .Ft uintmax_t value. .Fn strtou function uses internally .Fn strtoumax and ensures that the result is always in the range [ .Fa lo .. .Fa hi ]. In adddition it always places .Dv 0 on success or a conversion status in the .Fa rstatus argument, avoiding the .Dv errno gymnastics the other functions require. The .Fa rstatus argument can be .Dv NULL if conversion status is to be ignored. The .Fn strtouq function converts the string in .Fa nptr to a .Ft u_quad_t value. The conversion is done according to the given .Fa base , which must be between 2 and 36 inclusive, or be the special value 0.
p The string may begin with an arbitrary amount of white space (as determined by .Xr isspace 3 ) followed by a single optional .Ql + or .Ql - sign. If .Fa base is zero or 16, the string may then include a .Ql 0x prefix, and the number will be read in base 16; otherwise, a zero .Fa base is taken as 10 (decimal) unless the next character is .Ql 0 , in which case it is taken as 8 (octal).
p The remainder of the string is converted to an .Em unsigned long value in the obvious manner, stopping at the end of the string or at the first character that does not produce a valid digit in the given base. (In bases above 10, the letter .Ql A in either upper or lower case represents 10, .Ql B represents 11, and so forth, with .Ql Z representing 35.)
p If .Fa endptr is non-nil, .Fn strtoul stores the address of the first invalid character in .Fa *endptr . If there were no digits at all, however, .Fn strtoul stores the original value of .Fa nptr in .Fa *endptr . (Thus, if .Fa *nptr is not .Ql \e0 but .Fa **endptr is .Ql \e0 on return, the entire string was valid.) .Sh RETURN VALUES The .Fn strtou function always returns the closest value in the range specified by the .Fa lo and .Fa hi arguments. The .Fn strtoul function returns either the result of the conversion or, if there was a leading minus sign, the negation of the result of the conversion, unless the original (non-negated) value would overflow; in the latter case, .Fn strtoul returns .Dv ULONG_MAX , .Fn strtoull returns .Dv ULLONG_MAX , .Fn strtoumax returns .Dv UINTMAX_MAX , .Fn strtouq returns .Dv UQUAD_MAX , and the global variable .Va errno is set to .Er ERANGE .
p There is no way to determine if .Fn strtoul has processed a negative number (and returned an unsigned value) short of examining the string in .Fa nptr directly. If the .Fa base argument is not supported then .Va errno is set to .Er EINVAL and the functions return 0.
p If no error occurs, .Va errno is left unchanged. This behavior (which is unlike most library functions) is guaranteed by the pertinent standards. .Sh EXAMPLES The .Fn strtou function is the simplest to use: d -literal -offset indent int e; uintmax_t lval = strtou(buf, NULL, 0, 1, 99, &e); if (e) warn("conversion of `%s' to a number failed, using %ju", buf, lval); .Ed
p This will always return a number in .Dv [1..99] range no matter what the input is, and warn if the conversion failed.
p Because the return value of .Fn strtoul cannot be used unambiguously to detect an error, .Va errno is left unchanged after a successful call. To ensure that a string is a valid number (i.e., in range and containing no trailing characters), clear .Va errno beforehand explicitly, then check it afterwards: d -literal -offset indent char *ep; unsigned long ulval; ... errno = 0; ulval = strtoul(buf, \*[Am]ep, 10); if (buf[0] == '\e0' || *ep != '\e0') goto not_a_number; if (errno == ERANGE \*[Am]\*[Am] ulval == ULONG_MAX) goto out_of_range; .Ed
p This example will accept .Dq 12 but not .Dq 12foo or .Dq 12\en . If trailing whitespace is acceptable, further checks must be done on .Va *ep ; alternately, use .Xr sscanf 3 . .Sh ERRORS l -tag -width Er t Bq Er EINVAL The .Ar base is not between 2 and 36 and does not contain the special value 0. t Bq Er ERANGE The given string was out of range; the value converted has been clamped. .El
p In addition to the above errors .Fn strtou returns: l -tag -width Er t Bq Er ECANCELED The string did not contain any characters that were converted. t Bq Er ENOTSUP The string contained non-numeric characters that did not get converted. In this case, .Fa endptr points to the first unconverted character. t Bq Er ERANGE The range given was invalid, i.e. .Fa lo \*[Gt] .Fa hi . .El .Sh SEE ALSO .Xr strtoi 3 , .Xr strtoimax 3 , .Xr strtol 3 , .Xr strtoll 3 .Sh STANDARDS The .Fn strtoul function conforms to .St -ansiC . The .Fn strtoull and .Fn strtoumax functions conform to .St -isoC-99 . The .Fn strtou function appeared in .Nx 8 . .Sh BUGS Ignores the current locale.