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| <h4 class="subsection">12.14.6 Dynamically Allocating String Conversions</h4> |
| |
| <p>A GNU extension to formatted input lets you safely read a string with no |
| maximum size. Using this feature, you don't supply a buffer; instead, |
| <code>scanf</code> allocates a buffer big enough to hold the data and gives |
| you its address. To use this feature, write ‘<samp><span class="samp">a</span></samp>’ as a flag |
| character, as in ‘<samp><span class="samp">%as</span></samp>’ or ‘<samp><span class="samp">%a[0-9a-z]</span></samp>’. |
| |
| <p>The pointer argument you supply for where to store the input should have |
| type <code>char **</code>. The <code>scanf</code> function allocates a buffer and |
| stores its address in the word that the argument points to. You should |
| free the buffer with <code>free</code> when you no longer need it. |
| |
| <p>Here is an example of using the ‘<samp><span class="samp">a</span></samp>’ flag with the ‘<samp><span class="samp">%[...]</span></samp>’ |
| conversion specification to read a “variable assignment” of the form |
| ‘<samp><var>variable</var><span class="samp"> = </span><var>value</var></samp>’. |
| |
| <pre class="smallexample"> { |
| char *variable, *value; |
| |
| if (2 > scanf ("%a[a-zA-Z0-9] = %a[^\n]\n", |
| &variable, &value)) |
| { |
| invalid_input_error (); |
| return 0; |
| } |
| |
| ... |
| } |
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