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<title>The GNU Fortran Compiler: BOZ literal constants</title>
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<a name="BOZ-literal-constants"></a>
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<p>
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Next: <a href="Real-array-indices.html#Real-array-indices" accesskey="n" rel="next">Real array indices</a>, Previous: <a href="Q-exponent_002dletter.html#Q-exponent_002dletter" accesskey="p" rel="prev"><code>Q</code> exponent-letter</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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<a name="BOZ-literal-constants-1"></a>
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<h4 class="subsection">6.1.9 BOZ literal constants</h4>
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<a name="index-BOZ-literal-constants"></a>
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<p>Besides decimal constants, Fortran also supports binary (<code>b</code>),
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octal (<code>o</code>) and hexadecimal (<code>z</code>) integer constants. The
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syntax is: ‘<samp>prefix quote digits quote</samp>’, were the prefix is
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either <code>b</code>, <code>o</code> or <code>z</code>, quote is either <code>'</code> or
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<code>"</code> and the digits are for binary <code>0</code> or <code>1</code>, for
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octal between <code>0</code> and <code>7</code>, and for hexadecimal between
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<code>0</code> and <code>F</code>. (Example: <code>b'01011101'</code>.)
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</p>
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<p>Up to Fortran 95, BOZ literals were only allowed to initialize
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integer variables in DATA statements. Since Fortran 2003 BOZ literals
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are also allowed as argument of <code>REAL</code>, <code>DBLE</code>, <code>INT</code>
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and <code>CMPLX</code>; the result is the same as if the integer BOZ
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literal had been converted by <code>TRANSFER</code> to, respectively,
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<code>real</code>, <code>double precision</code>, <code>integer</code> or <code>complex</code>.
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As GNU Fortran extension the intrinsic procedures <code>FLOAT</code>,
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<code>DFLOAT</code>, <code>COMPLEX</code> and <code>DCMPLX</code> are treated alike.
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</p>
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<p>As an extension, GNU Fortran allows hexadecimal BOZ literal constants to
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be specified using the <code>X</code> prefix, in addition to the standard
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<code>Z</code> prefix. The BOZ literal can also be specified by adding a
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suffix to the string, for example, <code>Z'ABC'</code> and <code>'ABC'Z</code> are
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equivalent.
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</p>
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<p>Furthermore, GNU Fortran allows using BOZ literal constants outside
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DATA statements and the four intrinsic functions allowed by Fortran 2003.
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In DATA statements, in direct assignments, where the right-hand side
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only contains a BOZ literal constant, and for old-style initializers of
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the form <code>integer i /o'0173'/</code>, the constant is transferred
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as if <code>TRANSFER</code> had been used; for <code>COMPLEX</code> numbers, only
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the real part is initialized unless <code>CMPLX</code> is used. In all other
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cases, the BOZ literal constant is converted to an <code>INTEGER</code> value with
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the largest decimal representation. This value is then converted
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numerically to the type and kind of the variable in question.
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(For instance, <code>real :: r = b'0000001' + 1</code> initializes <code>r</code>
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with <code>2.0</code>.) As different compilers implement the extension
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differently, one should be careful when doing bitwise initialization
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of non-integer variables.
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</p>
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<p>Note that initializing an <code>INTEGER</code> variable with a statement such
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as <code>DATA i/Z'FFFFFFFF'/</code> will give an integer overflow error rather
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than the desired result of <em>-1</em> when <code>i</code> is a 32-bit integer
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on a system that supports 64-bit integers. The ‘<samp>-fno-range-check</samp>’
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option can be used as a workaround for legacy code that initializes
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integers in this manner.
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Next: <a href="Real-array-indices.html#Real-array-indices" accesskey="n" rel="next">Real array indices</a>, Previous: <a href="Q-exponent_002dletter.html#Q-exponent_002dletter" accesskey="p" rel="prev"><code>Q</code> exponent-letter</a>, Up: <a href="Extensions-implemented-in-GNU-Fortran.html#Extensions-implemented-in-GNU-Fortran" accesskey="u" rel="up">Extensions implemented in GNU Fortran</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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