Sophie: php-manual-en-4.3.0-2mdk noarch

php-manual-en-4.3.0-2mdk.noarch.rpm

<HTML
><HEAD
><TITLE
>Floating point numbers</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
REL="HOME"
TITLE="PHP Manual"
HREF="index.html"><LINK
REL="UP"
TITLE="Types"
HREF="language.types.html"><LINK
REL="PREVIOUS"
TITLE="Integers"
HREF="language.types.integer.html"><LINK
REL="NEXT"
TITLE="Strings"
HREF="language.types.string.html"><META
HTTP-EQUIV="Content-type"
CONTENT="text/html; charset=ISO-8859-1"></HEAD
><BODY
CLASS="sect1"
BGCOLOR="#FFFFFF"
TEXT="#000000"
LINK="#0000FF"
VLINK="#840084"
ALINK="#0000FF"
><DIV
CLASS="NAVHEADER"
><TABLE
SUMMARY="Header navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>PHP Manual</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="language.types.integer.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 7. Types</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="language.types.string.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="sect1"
><H1
CLASS="sect1"
><A
NAME="language.types.float"
></A
>Floating point numbers</H1
><P
>&#13;    Floating point numbers (AKA "floats", "doubles" or "real numbers") can be 
    specified using any of the following syntaxes: 
    <DIV
CLASS="informalexample"
><A
NAME="AEN3373"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>&#60;?php
$a = 1.234; 
$b = 1.2e3; 
$c = 7E-10;
?&#62;</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    Formally:
    <DIV
CLASS="informalexample"
><A
NAME="AEN3375"
></A
><P
></P
><TABLE
BORDER="0"
BGCOLOR="#E0E0E0"
CELLPADDING="5"
><TR
><TD
><PRE
CLASS="php"
>LNUM          [0-9]+
DNUM          ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM ( ({LNUM} | {DNUM}) [eE][+-]? {LNUM})</PRE
></TD
></TR
></TABLE
><P
></P
></DIV
>
    The size of a float is platform-dependent, 
    although a maximum of ~1.8e308 with a precision of roughly 14 
    decimal digits is a common value (that's 64 bit IEEE format).
   </P
><DIV
CLASS="warning"
><P
></P
><TABLE
CLASS="warning"
BORDER="1"
WIDTH="100%"
><TR
><TD
ALIGN="CENTER"
><B
><A
NAME="warn.float-precision"
></A
>Floating point precision</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
>&#13;     It is quite usual that simple decimal fractions like
     <TT
CLASS="literal"
>0.1</TT
> or <TT
CLASS="literal"
>0.7</TT
> cannot be
     converted into their internal binary counterparts without a
     little loss of precision. This can lead to confusing results: for
     example, <TT
CLASS="literal"
>floor((0.1+0.7)*10)</TT
> will usually
     return <TT
CLASS="literal"
>7</TT
> instead of the expected
     <TT
CLASS="literal"
>8</TT
> as the result of the internal representation
     really being something like <TT
CLASS="literal"
>7.9999999999...</TT
>.
    </P
><P
>&#13;     This is related to the fact that it is impossible to exactly
     express some fractions in decimal notation with a finite number
     of digits. For instance, <TT
CLASS="literal"
>1/3</TT
> in decimal form
     becomes <TT
CLASS="literal"
>0.3333333. . .</TT
>.
    </P
><P
>&#13;     So never trust floating number results to the last digit and
     never compare floating point numbers for equality. If you really
     need higher precision, you should use the <A
HREF="ref.bc.html"
>arbitrary precision math functions</A
>
     or <A
HREF="ref.gmp.html"
>gmp</A
> functions instead.
    </P
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="sect2"
><H2
CLASS="sect2"
><A
NAME="language.types.float.casting"
></A
>Converting to float</H2
><P
>&#13;     For information on when and how strings are converted to floats,
     see the section titled <A
HREF="language.types.string.html#language.types.string.conversion"
>String
     conversion to numbers</A
>. For values of other types, the conversion
     is the same as if the value would have been converted to integer
     and then to float. See the <A
HREF="language.types.integer.html#language.types.integer.casting"
>Converting
     to integer</A
> section for more information.
    </P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
SUMMARY="Footer navigation table"
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="language.types.integer.html"
ACCESSKEY="P"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="index.html"
ACCESSKEY="H"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="language.types.string.html"
ACCESSKEY="N"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Integers</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="language.types.html"
ACCESSKEY="U"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Strings</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>