devdocs/c/numeric%2Fmath%2Ffp_categories.html


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    <h1 id="firstHeading" class="firstHeading">FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN</h1>            <table class="t-dcl-begin"> <tr class="t-dsc-header"> <th> Defined in header <code>&lt;math.h&gt;</code> </th> <th> </th> <th> </th> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define FP_NORMAL    /*implementation defined*/</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define FP_SUBNORMAL /*implementation defined*/</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define FP_ZERO      /*implementation defined*/</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define FP_INFINITE  /*implementation defined*/</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr> <tr class="t-dcl t-since-c99"> <td> <pre data-language="c">#define FP_NAN       /*implementation defined*/</pre>
</td> <td class="t-dcl-nopad"> </td> <td> <span class="t-mark-rev t-since-c99">(since C99)</span> </td> </tr>  </table> <p>The <code>FP_NORMAL</code>, <code>FP_SUBNORMAL</code>, <code>FP_ZERO</code>, <code>FP_INFINITE</code>, <code>FP_NAN</code> macros each represent a distinct category of floating-point numbers. They all expand to an integer constant expression.</p>
<table class="t-dsc-begin"> <tr class="t-dsc-hitem"> <th> Constant </th> <th> Explanation </th>
</tr> <tr class="t-dsc"> <td> <code>FP_NORMAL</code> </td> <td> indicates that the value is <i>normal</i>, i.e. not an infinity, subnormal, not-a-number or zero </td>
</tr> <tr class="t-dsc"> <td> <code>FP_SUBNORMAL</code> </td> <td> indicates that the value is <a href="https://en.wikipedia.org/wiki/Subnormal_number" class="extiw" title="enwiki:Subnormal number"><i>subnormal</i></a> </td>
</tr> <tr class="t-dsc"> <td> <code>FP_ZERO</code> </td> <td> indicates that the value is positive or negative zero </td>
</tr> <tr class="t-dsc"> <td> <code>FP_INFINITE</code> </td> <td> indicates that the value is not representable by the underlying type (positive or negative infinity) </td>
</tr> <tr class="t-dsc"> <td> <code>FP_NAN</code> </td> <td> indicates that the value is not-a-number (NaN) </td>
</tr> </table> <h3 id="Example"> Example</h3> <div class="t-example"> <div class="c source-c"><pre data-language="c">#include &lt;stdio.h&gt;
#include &lt;math.h&gt;
#include &lt;float.h&gt;
 
const char *show_classification(double x) {
    switch(fpclassify(x)) {
        case FP_INFINITE:  return "Inf";
        case FP_NAN:       return "NaN";
        case FP_NORMAL:    return "normal";
        case FP_SUBNORMAL: return "subnormal";
        case FP_ZERO:      return "zero";
        default:           return "unknown";
    }
}
int main(void)
{
    printf("1.0/0.0 is %s\n", show_classification(1/0.0));
    printf("0.0/0.0 is %s\n", show_classification(0.0/0.0));
    printf("DBL_MIN/2 is %s\n", show_classification(DBL_MIN/2));
    printf("-0.0 is %s\n", show_classification(-0.0));
    printf(" 1.0 is %s\n", show_classification(1.0));
}</pre></div> <p>Output:</p>
<div class="text source-text"><pre data-language="c">1.0/0.0 is Inf
0.0/0.0 is NaN
DBL_MIN/2 is subnormal
-0.0 is zero
 1.0 is normal</pre></div> </div> <h3 id="References"> References</h3>  <ul>
<li> C17 standard (ISO/IEC 9899:2018): </li>
<ul><li> 7.12/6 FP_NORMAL, ... (p: 169-170) </li></ul>
<li> C11 standard (ISO/IEC 9899:2011): </li>
<ul><li> 7.12/6 FP_NORMAL, ... (p: 232) </li></ul>
<li> C99 standard (ISO/IEC 9899:1999): </li>
<ul><li> 7.12/6 FP_NORMAL, ... (p: 213) </li></ul>
</ul>           <h3 id="See_also"> See also</h3> <table class="t-dsc-begin"> <tr class="t-dsc"> <td> <div><a href="fpclassify" title="c/numeric/math/fpclassify"> <span class="t-lines"><span>fpclassify</span></span></a></div>
<div><span class="t-lines"><span><span class="t-mark-rev t-since-c99">(C99)</span></span></span></div> </td> <td> classifies the given floating-point value <br> <span class="t-mark">(function macro)</span>  </td>
</tr> <tr class="t-dsc"> <td colspan="2"> <span><a href="https://en.cppreference.com/w/cpp/numeric/math/FP_categories" title="cpp/numeric/math/FP categories">C++ documentation</a></span> for <code>FP_categories</code> </td>
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