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<a name="strtol_002d_002d_002dstring-to-long"></a>
<h3 class="section">2.38 <code>strtol</code>&mdash;string to long</h3>
<a name="index-strtol"></a>
<a name="index-_005fstrtol_005fr"></a>
<p><strong>Synopsis</strong>
</p><div class="example">
<pre class="example">#include &lt;stdlib.h&gt;
long strtol(const char *restrict <var>s</var>, char **restrict <var>ptr</var>,int <var>base</var>);

long _strtol_r(void *<var>reent</var>, 
    const char *restrict <var>s</var>, char **restrict <var>ptr</var>,int <var>base</var>);

</pre></div>
<p><strong>Description</strong><br>
The function <code>strtol</code> converts the string <code>*<var>s</var></code> to
a <code>long</code>. First, it breaks down the string into three parts:
leading whitespace, which is ignored; a subject string consisting
of characters resembling an integer in the radix specified by <var>base</var>;
and a trailing portion consisting of zero or more unparseable characters,
and always including the terminating null character. Then, it attempts
to convert the subject string into a <code>long</code> and returns the
result.
</p>
<p>If the value of <var>base</var> is 0, the subject string is expected to look
like a normal C integer constant: an optional sign, a possible &lsquo;<code>0x</code>&rsquo;
indicating a hexadecimal base, and a number. If <var>base</var> is between
2 and 36, the expected form of the subject is a sequence of letters
and digits representing an integer in the radix specified by <var>base</var>,
with an optional plus or minus sign. The letters <code>a</code>&ndash;<code>z</code> (or,
equivalently, <code>A</code>&ndash;<code>Z</code>) are used to signify values from 10 to 35;
only letters whose ascribed values are less than <var>base</var> are
permitted. If <var>base</var> is 16, a leading <code>0x</code> is permitted.
</p>
<p>The subject sequence is the longest initial sequence of the input
string that has the expected form, starting with the first
non-whitespace character.  If the string is empty or consists entirely
of whitespace, or if the first non-whitespace character is not a
permissible letter or digit, the subject string is empty.
</p>
<p>If the subject string is acceptable, and the value of <var>base</var> is zero,
<code>strtol</code> attempts to determine the radix from the input string. A
string with a leading <code>0x</code> is treated as a hexadecimal value; a string with
a leading 0 and no <code>x</code> is treated as octal; all other strings are
treated as decimal. If <var>base</var> is between 2 and 36, it is used as the
conversion radix, as described above. If the subject string begins with
a minus sign, the value is negated. Finally, a pointer to the first
character past the converted subject string is stored in <var>ptr</var>, if
<var>ptr</var> is not <code>NULL</code>.
</p>
<p>If the subject string is empty (or not in acceptable form), no conversion
is performed and the value of <var>s</var> is stored in <var>ptr</var> (if <var>ptr</var> is
not <code>NULL</code>).
</p>
<p>The alternate function <code>_strtol_r</code> is a reentrant version.  The
extra argument <var>reent</var> is a pointer to a reentrancy structure.
</p>
<br>
<p><strong>Returns</strong><br>
<code>strtol</code> returns the converted value, if any. If no conversion was
made, 0 is returned.
</p>
<p><code>strtol</code> returns <code>LONG_MAX</code> or <code>LONG_MIN</code> if the magnitude of
the converted value is too large, and sets <code>errno</code> to <code>ERANGE</code>.
</p>
<br>
<p><strong>Portability</strong><br>
<code>strtol</code> is ANSI.
</p>
<p>No supporting OS subroutines are required.
</p>
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