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<h4 class="subsection">6.1.9 BOZ literal constants</h4>
<p><a name="index-BOZ-literal-constants-311"></a>
Besides decimal constants, Fortran also supports binary (<code>b</code>),
octal (<code>o</code>) and hexadecimal (<code>z</code>) integer constants. The
syntax is: ‘<samp><span class="samp">prefix quote digits quote</span></samp>’, were the prefix is
either <code>b</code>, <code>o</code> or <code>z</code>, quote is either <code>'</code> or
<code>"</code> and the digits are for binary <code>0</code> or <code>1</code>, for
octal between <code>0</code> and <code>7</code>, and for hexadecimal between
<code>0</code> and <code>F</code>. (Example: <code>b'01011101'</code>.)
<p>Up to Fortran 95, BOZ literals were only allowed to initialize
integer variables in DATA statements. Since Fortran 2003 BOZ literals
are also allowed as argument of <code>REAL</code>, <code>DBLE</code>, <code>INT</code>
and <code>CMPLX</code>; the result is the same as if the integer BOZ
literal had been converted by <code>TRANSFER</code> to, respectively,
<code>real</code>, <code>double precision</code>, <code>integer</code> or <code>complex</code>.
As GNU Fortran extension the intrinsic procedures <code>FLOAT</code>,
<code>DFLOAT</code>, <code>COMPLEX</code> and <code>DCMPLX</code> are treated alike.
<p>As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
be specified using the <code>X</code> prefix, in addition to the standard
<code>Z</code> prefix. The BOZ literal can also be specified by adding a
suffix to the string, for example, <code>Z'ABC'</code> and <code>'ABC'Z</code> are
equivalent.
<p>Furthermore, GNU Fortran allows using BOZ literal constants outside
DATA statements and the four intrinsic functions allowed by Fortran 2003.
In DATA statements, in direct assignments, where the right-hand side
only contains a BOZ literal constant, and for old-style initializers of
the form <code>integer i /o'0173'/</code>, the constant is transferred
as if <code>TRANSFER</code> had been used; for <code>COMPLEX</code> numbers, only
the real part is initialized unless <code>CMPLX</code> is used. In all other
cases, the BOZ literal constant is converted to an <code>INTEGER</code> value with
the largest decimal representation. This value is then converted
numerically to the type and kind of the variable in question.
(For instance, <code>real :: r = b'0000001' + 1</code> initializes <code>r</code>
with <code>2.0</code>.) As different compilers implement the extension
differently, one should be careful when doing bitwise initialization
of non-integer variables.
<p>Note that initializing an <code>INTEGER</code> variable with a statement such
as <code>DATA i/Z'FFFFFFFF'/</code> will give an integer overflow error rather
than the desired result of -1 when <code>i</code> is a 32-bit integer
on a system that supports 64-bit integers. The ‘<samp><span class="samp">-fno-range-check</span></samp>’
option can be used as a workaround for legacy code that initializes
integers in this manner.
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