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| <a name="Hollerith-constants-support-1"></a> |
| <h4 class="subsection">6.1.13 Hollerith constants support</h4> |
| <a name="index-Hollerith-constants"></a> |
| |
| <p>GNU Fortran supports Hollerith constants in assignments, function |
| arguments, and <code>DATA</code> and <code>ASSIGN</code> statements. A Hollerith |
| constant is written as a string of characters preceded by an integer |
| constant indicating the character count, and the letter <code>H</code> or |
| <code>h</code>, and stored in bytewise fashion in a numeric (<code>INTEGER</code>, |
| <code>REAL</code>, or <code>complex</code>) or <code>LOGICAL</code> variable. The |
| constant will be padded or truncated to fit the size of the variable in |
| which it is stored. |
| </p> |
| <p>Examples of valid uses of Hollerith constants: |
| </p><div class="smallexample"> |
| <pre class="smallexample"> complex*16 x(2) |
| data x /16Habcdefghijklmnop, 16Hqrstuvwxyz012345/ |
| x(1) = 16HABCDEFGHIJKLMNOP |
| call foo (4h abc) |
| </pre></div> |
| |
| <p>Invalid Hollerith constants examples: |
| </p><div class="smallexample"> |
| <pre class="smallexample"> integer*4 a |
| a = 8H12345678 ! Valid, but the Hollerith constant will be truncated. |
| a = 0H ! At least one character is needed. |
| </pre></div> |
| |
| <p>In general, Hollerith constants were used to provide a rudimentary |
| facility for handling character strings in early Fortran compilers, |
| prior to the introduction of <code>CHARACTER</code> variables in Fortran 77; |
| in those cases, the standard-compliant equivalent is to convert the |
| program to use proper character strings. On occasion, there may be a |
| case where the intent is specifically to initialize a numeric variable |
| with a given byte sequence. In these cases, the same result can be |
| obtained by using the <code>TRANSFER</code> statement, as in this example. |
| </p><div class="smallexample"> |
| <pre class="smallexample"> INTEGER(KIND=4) :: a |
| a = TRANSFER ("abcd", a) ! equivalent to: a = 4Habcd |
| </pre></div> |
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