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| <h3 class="section">1.33 <code>log</code>, <code>logf</code>—natural logarithms</h3> |
| |
| <p><a name="index-log-98"></a><a name="index-logf-99"></a><strong>Synopsis</strong> |
| <pre class="example"> #include <math.h> |
| double log(double <var>x</var>); |
| float logf(float <var>x</var>); |
| |
| </pre> |
| <p><strong>Description</strong><br> |
| Return the natural logarithm of <var>x</var>, that is, its logarithm base e |
| (where e is the base of the natural system of logarithms, 2.71828<small class="dots">...</small>). |
| <code>log</code> and <code>logf</code> are identical save for the return and argument types. |
| |
| <p>You can use the (non-ANSI) function <code>matherr</code> to specify error |
| handling for these functions. |
| |
| <p><br> |
| <strong>Returns</strong><br> |
| Normally, returns the calculated value. When <var>x</var> is zero, the |
| returned value is <code>-HUGE_VAL</code> and <code>errno</code> is set to <code>ERANGE</code>. |
| When <var>x</var> is negative, the returned value is NaN (not a number) and |
| <code>errno</code> is set to <code>EDOM</code>. You can control the error behavior via |
| <code>matherr</code>. |
| |
| <p><br> |
| <strong>Portability</strong><br> |
| <code>log</code> is ANSI. <code>logf</code> is an extension. |
| |
| <p><br> |
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