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| <title>The GNU Fortran Compiler: BOZ literal constants</title> |
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| <a name="BOZ-literal-constants-1"></a> |
| <h4 class="subsection">6.1.9 BOZ literal constants</h4> |
| <a name="index-BOZ-literal-constants"></a> |
| |
| <p>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>prefix quote digits quote</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> |
| <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> |
| <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> |
| <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> |
| <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 <em>-1</em> when <code>i</code> is a 32-bit integer |
| on a system that supports 64-bit integers. The ‘<samp>-fno-range-check</samp>’ |
| option can be used as a workaround for legacy code that initializes |
| integers in this manner. |
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