# strtoul

## PROLOG



           This manual page is part of the POSIX Programmer's Manual.  The
           Linux implementation of this interface may differ (consult the
           corresponding Linux manual page for details of Linux behavior), or
           the interface may not be implemented on Linux.
    


## NAME



           strtoul, strtoull — convert a string to an unsigned long
    


## SYNOPSIS



           #include <stdlib.h>
    
           unsigned long strtoul(const char *restrict _str_ ,
               char **restrict _endptr_ , int _base_);
           unsigned long long strtoull(const char *restrict _str_ ,
               char **restrict _endptr_ , int _base_);
    


## DESCRIPTION



           The functionality described on this reference page is aligned with
           the ISO C standard. Any conflict between the requirements
           described here and the ISO C standard is unintentional. This
           volume of POSIX.1‐2017 defers to the ISO C standard.
    
           These functions shall convert the initial portion of the string
           pointed to by _str_ to a type **unsigned long** and **unsigned long long**
           representation, respectively. First, they decompose the input
           string into three parts:
    
            1. An initial, possibly empty, sequence of white-space characters
               (as specified by _isspace_())
    
            2. A subject sequence interpreted as an integer represented in
               some radix determined by the value of _base_
    
            3. A final string of one or more unrecognized characters,
               including the terminating NUL character of the input string
    
           Then they shall attempt to convert the subject sequence to an
           unsigned integer, and return the result.
    
           If the value of _base_ is 0, the expected form of the subject
           sequence is that of a decimal constant, octal constant, or
           hexadecimal constant, any of which may be preceded by a **'+'** or **'-'**
           sign. A decimal constant begins with a non-zero digit, and
           consists of a sequence of decimal digits. An octal constant
           consists of the prefix **'0'** optionally followed by a sequence of
           the digits **'0'** to **'7'** only. A hexadecimal constant consists of the
           prefix 0x or 0X followed by a sequence of the decimal digits and
           letters **'a'**(or **'A'**) to **'f'**(or **'F'**) with values 10 to 15
           respectively.
    
           If the value of _base_ is between 2 and 36, the expected form of the
           subject sequence is a sequence of letters and digits representing
           an integer with the radix specified by _base_ , optionally preceded
           by a **'+'** or **'-'** sign. The letters from **'a'**(or **'A'**) to **'z'**(or
           **'Z'**) inclusive are ascribed the values 10 to 35; only letters
           whose ascribed values are less than that of _base_ are permitted. If
           the value of _base_ is 16, the characters 0x or 0X may optionally
           precede the sequence of letters and digits, following the sign if
           present.
    
           The subject sequence is defined as the longest initial subsequence
           of the input string, starting with the first non-white-space
           character that is of the expected form. The subject sequence shall
           contain no characters if the input string is empty or consists
           entirely of white-space characters, or if the first non-white-
           space character is other than a sign or a permissible letter or
           digit.
    
           If the subject sequence has the expected form and the value of
           _base_ is 0, the sequence of characters starting with the first
           digit shall be interpreted as an integer constant. If the subject
           sequence has the expected form and the value of _base_ is between 2
           and 36, it shall be used as the base for conversion, ascribing to
           each letter its value as given above. If the subject sequence
           begins with a <hyphen-minus>, the value resulting from the
           conversion shall be negated. A pointer to the final string shall
           be stored in the object pointed to by _endptr_ , provided that _endptr_
           is not a null pointer.
    
           In other than the C or POSIX locale, additional locale-specific
           subject sequence forms may be accepted.
    
           If the subject sequence is empty or does not have the expected
           form, no conversion shall be performed; the value of _str_ shall be
           stored in the object pointed to by _endptr_ , provided that _endptr_ is
           not a null pointer.
    
           These functions shall not change the setting of _errno_ if
           successful.
    
           Since 0, {ULONG_MAX}, and {ULLONG_MAX} are returned on error and
           are also valid returns on success, an application wishing to check
           for error situations should set _errno_ to 0, then call _strtoul_() or
           _strtoull_(), then check _errno_.
    


## RETURN VALUE



           Upon successful completion, these functions shall return the
           converted value, if any. If no conversion could be performed, 0
           shall be returned and _errno_ may be set to **[EINVAL]**.
    
           If the value of _base_ is not supported, 0 shall be returned and
           _errno_ shall be set to **[EINVAL]**.
    
           If the correct value is outside the range of representable values,
           {ULONG_MAX} or {ULLONG_MAX} shall be returned and _errno_ set to
           **[ERANGE]**.
    


## ERRORS



           These functions shall fail if:
    
           **EINVAL** The value of _base_ is not supported.
    
           **ERANGE** The value to be returned is not representable.
    
           These functions may fail if:
    
           **EINVAL** No conversion could be performed.
    
           _The following sections are informative._
    


## EXAMPLES



           None.
    


## APPLICATION USAGE



           Since the value of _*endptr_ is unspecified if the value of _base_ is
           not supported, applications should either ensure that _base_ has a
           supported value (0 or between 2 and 36) before the call, or check
           for an **[EINVAL]** error before examining _*endptr_.
    


## RATIONALE



           None.
    


## FUTURE DIRECTIONS



           None.
    


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