This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee  document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                        STRTOL(3POSIX)

       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 nptr to a type long and
       longlong 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 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  is  performed;  the
       value  of  nptr  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, {LONG_MIN} or {LLONG_MIN}, and {LONG_MAX} or {LLONG_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 strtol() or strtoll(), then check errno.

       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.

       Thefollowingsectionsareinformative.

       None.

       None.

       strtol, strtoll — convert a string to a long integer

       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.

       None.

       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, {LONG_MIN}, {LONG_MAX}, {LLONG_MIN},
       or {LLONG_MAX} shall be returned (according to the sign of the value), and errno set to [ERANGE].

fscanf(), isalpha(), strtod()

       The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

       #include <stdlib.h>

       long strtol(const char *restrict nptr, char **restrict endptr, int base);
       long long strtoll(const char *restrict nptr, char **restrict endptr,
           int base)