strtoul(3)

1strtoul(3)                 Library Functions Manual                 strtoul(3)
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NAME

6       strtoul, strtoull, strtouq - convert a string to an unsigned long inte‐
7       ger
8

LIBRARY

10       Standard C library (libc, -lc)
11

SYNOPSIS

13       #include <stdlib.h>
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15       unsigned long strtoul(const char *restrict nptr,
16                             char **restrict endptr, int base);
17       unsigned long long strtoull(const char *restrict nptr,
18                             char **restrict endptr, int base);
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20   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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22       strtoull():
23           _ISOC99_SOURCE
24               || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
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DESCRIPTION

27       The strtoul() function converts the initial part of the string in  nptr
28       to  an  unsigned  long value according to the given base, which must be
29       between 2 and 36 inclusive, or be the special value 0.
30
31       The string may begin with an arbitrary amount of white space (as deter‐
32       mined by isspace(3)) followed by a single optional '+' or '-' sign.  If
33       base is zero or 16, the string may then include a "0x" prefix, and  the
34       number  will  be read in base 16; otherwise, a zero base is taken as 10
35       (decimal) unless the next character is '0', in which case it  is  taken
36       as 8 (octal).
37
38       The  remainder  of the string is converted to an unsigned long value in
39       the obvious manner, stopping at the first  character  which  is  not  a
40       valid  digit  in the given base.  (In bases above 10, the letter 'A' in
41       either uppercase or lowercase represents 10, 'B' represents 11, and  so
42       forth, with 'Z' representing 35.)
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44       If  endptr  is  not NULL, strtoul() stores the address of the first in‐
45       valid character in *endptr.  If there were no digits at all,  strtoul()
46       stores  the original value of nptr in *endptr (and returns 0).  In par‐
47       ticular, if *nptr is not '\0' but **endptr is '\0' on return,  the  en‐
48       tire string is valid.
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50       The  strtoull() function works just like the strtoul() function but re‐
51       turns an unsigned long long value.
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RETURN VALUE

54       The strtoul() function returns either the result of the conversion  or,
55       if  there  was  a leading minus sign, the negation of the result of the
56       conversion represented as an unsigned value, unless the original  (non‐
57       negated)  value  would  overflow; in the latter case, strtoul() returns
58       ULONG_MAX and sets errno to ERANGE.  Precisely the same holds for  str‐
59       toull() (with ULLONG_MAX instead of ULONG_MAX).
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ERRORS

62       EINVAL (not in C99) The given base contains an unsupported value.
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64       ERANGE The resulting value was out of range.
65
66       The  implementation  may also set errno to EINVAL in case no conversion
67       was performed (no digits seen, and 0 returned).
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ATTRIBUTES

70       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
71       tributes(7).
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73       ┌─────────────────────────────────────┬───────────────┬────────────────┐
74       │Interface                            │ Attribute     │ Value          │
75       ├─────────────────────────────────────┼───────────────┼────────────────┤
76       │strtoul(), strtoull(), strtouq()     │ Thread safety │ MT-Safe locale │
77       └─────────────────────────────────────┴───────────────┴────────────────┘
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STANDARDS

80       C11, POSIX.1-2008.
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HISTORY

83       strtoul()
84              POSIX.1-2001, C89, SVr4.
85
86       strtoull()
87              POSIX.1-2001, C99.
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NOTES

90       Since  strtoul() can legitimately return 0 or ULONG_MAX (ULLONG_MAX for
91       strtoull()) on both success and failure, the calling program should set
92       errno  to 0 before the call, and then determine if an error occurred by
93       checking whether errno has a nonzero value after the call.
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95       In locales other than the "C" locale, other strings  may  be  accepted.
96       (For example, the thousands separator of the current locale may be sup‐
97       ported.)
98
99       BSD also has
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101           u_quad_t strtouq(const char *nptr, char **endptr, int base);
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103       with completely analogous definition.  Depending on the wordsize of the
104       current  architecture,  this may be equivalent to strtoull() or to str‐
105       toul().
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107       Negative values are considered valid input and are  silently  converted
108       to the equivalent unsigned long value.
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EXAMPLES

111       See  the example on the strtol(3) manual page; the use of the functions
112       described in this manual page is similar.
113