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<h1 id="firstHeading" class="firstHeading">modf, modff, modfl</h1> <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code><math.h></code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">float modff( float arg, float* iptr );</pre>
</td> <td> (1) </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl"> <td> <pre data-language="c">double modf( double arg, double* iptr );</pre>
</td> <td> (2) </td> <td class="t-dcl-nopad"> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">long double modfl( long double arg, long double* iptr );</pre>
</td> <td> (3) </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> </table> <div class="t-li1">
<span class="t-li">1-3)</span> Decomposes given floating point value <code>arg</code> into integral and fractional parts, each having the same type and sign as <code>arg</code>. The integral part (in floating-point format) is stored in the object pointed to by <code>iptr</code>.</div> <h3 id="Parameters"> Parameters</h3> <table class="t-par-begin"> <tr class="t-par"> <td> arg </td> <td> - </td> <td> floating point value </td>
</tr> <tr class="t-par"> <td> iptr </td> <td> - </td> <td> pointer to floating point value to store the integral part to </td>
</tr>
</table> <h3 id="Return_value"> Return value</h3> <p>If no errors occur, returns the fractional part of <code>x</code> with the same sign as <code>x</code>. The integral part is put into the value pointed to by <code>iptr</code>.</p>
<p>The sum of the returned value and the value stored in <code>*iptr</code> gives <code>arg</code> (allowing for rounding).</p>
<h3 id="Error_handling"> Error handling</h3> <p>This function is not subject to any errors specified in <a href="math_errhandling" title="c/numeric/math/math errhandling">math_errhandling</a>.</p>
<p>If the implementation supports IEEE floating-point arithmetic (IEC 60559),</p>
<ul>
<li> If <code>arg</code> is ±0, ±0 is returned, and ±0 is stored in <code>*iptr</code>. </li>
<li> If <code>arg</code> is ±∞, ±0 is returned, and ±∞ is stored in <code>*iptr</code>. </li>
<li> If <code>arg</code> is NaN, NaN is returned, and NaN is stored in <code>*iptr</code>. </li>
<li> The returned value is exact, <a href="../fenv/fe_round" title="c/numeric/fenv/FE round">the current rounding mode</a> is ignored </li>
</ul> <h3 id="Notes"> Notes</h3> <p>This function behaves as if implemented as follows:</p>
<div class="c source-c"><pre data-language="c">double modf(double value, double *iptr)
{
#pragma STDC FENV_ACCESS ON
int save_round = fegetround();
fesetround(FE_TOWARDZERO);
*iptr = std::nearbyint(value);
fesetround(save_round);
return copysign(isinf(value) ? 0.0 : value - (*iptr), value);
}</pre></div> <h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include <stdio.h>
#include <math.h>
#include <float.h>
int main(void)
{
double f = 123.45;
printf("Given the number %.2f or %a in hex,\n", f, f);
double f3;
double f2 = modf(f, &f3);
printf("modf() makes %.2f + %.2f\n", f3, f2);
int i;
f2 = frexp(f, &i);
printf("frexp() makes %f * 2^%d\n", f2, i);
i = ilogb(f);
printf("logb()/ilogb() make %f * %d^%d\n", f/scalbn(1.0, i), FLT_RADIX, i);
// special values
f2 = modf(-0.0, &f3);
printf("modf(-0) makes %.2f + %.2f\n", f3, f2);
f2 = modf(-INFINITY, &f3);
printf("modf(-Inf) makes %.2f + %.2f\n", f3, f2);
}</pre></div> <p>Possible output:</p>
<div class="text source-text"><pre data-language="c">Given the number 123.45 or 0x1.edccccccccccdp+6 in hex,
modf() makes 123.00 + 0.45
frexp() makes 0.964453 * 2^7
logb()/ilogb() make 1.92891 * 2^6
modf(-0) makes -0.00 + -0.00
modf(-Inf) makes -INF + -0.00</pre></div> </div> <h3 id="References"> References</h3> <ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul>
<li> 7.12.6.12 The modf functions (p: 246-247) </li>
<li> F.10.3.12 The modf functions (p: 523) </li>
</ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul>
<li> 7.12.6.12 The modf functions (p: 227) </li>
<li> F.9.3.12 The modf functions (p: 460) </li>
</ul>
<li> C89/C90 standard (ISO/IEC 9899:1990): </li>
<ul><li> 4.5.4.6 The modf function </li></ul>
</ul> <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="trunc" title="c/numeric/math/trunc"> <span class="t-lines"><span>trunc</span><span>truncf</span><span>truncl</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> rounds to nearest integer not greater in magnitude than the given value <br> <span class="t-mark">(function)</span> </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/numeric/math/modf" title="cpp/numeric/math/modf">C++ documentation</a></span> for <code>modf</code> </td>
</tr> </table> <div class="_attribution">
<p class="_attribution-p">
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<a href="https://en.cppreference.com/w/c/numeric/math/modf" class="_attribution-link">https://en.cppreference.com/w/c/numeric/math/modf</a>
</p>
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