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| <h4 class="subsection">12.12.8 Dynamically Allocating Formatted Output</h4> |
| |
| <p>The functions in this section do formatted output and place the results |
| in dynamically allocated memory. |
| |
| <!-- stdio.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>asprintf</b> (<var>char **ptr, const char *template, <small class="dots">...</small></var>)<var><a name="index-asprintf-1034"></a></var><br> |
| <blockquote><p>This function is similar to <code>sprintf</code>, except that it dynamically |
| allocates a string (as with <code>malloc</code>; see <a href="Unconstrained-Allocation.html#Unconstrained-Allocation">Unconstrained Allocation</a>) to hold the output, instead of putting the output in a |
| buffer you allocate in advance. The <var>ptr</var> argument should be the |
| address of a <code>char *</code> object, and a successful call to |
| <code>asprintf</code> stores a pointer to the newly allocated string at that |
| location. |
| |
| <p>The return value is the number of characters allocated for the buffer, or |
| less than zero if an error occurred. Usually this means that the buffer |
| could not be allocated. |
| |
| <p>Here is how to use <code>asprintf</code> to get the same result as the |
| <code>snprintf</code> example, but more easily: |
| |
| <pre class="smallexample"> /* <span class="roman">Construct a message describing the value of a variable</span> |
| <span class="roman">whose name is </span><var>name</var><span class="roman"> and whose value is </span><var>value</var><span class="roman">.</span> */ |
| char * |
| make_message (char *name, char *value) |
| { |
| char *result; |
| if (asprintf (&result, "value of %s is %s", name, value) < 0) |
| return NULL; |
| return result; |
| } |
| </pre> |
| </blockquote></div> |
| |
| <!-- stdio.h --> |
| <!-- GNU --> |
| <div class="defun"> |
| — Function: int <b>obstack_printf</b> (<var>struct obstack *obstack, const char *template, <small class="dots">...</small></var>)<var><a name="index-obstack_005fprintf-1035"></a></var><br> |
| <blockquote><p>This function is similar to <code>asprintf</code>, except that it uses the |
| obstack <var>obstack</var> to allocate the space. See <a href="Obstacks.html#Obstacks">Obstacks</a>. |
| |
| <p>The characters are written onto the end of the current object. |
| To get at them, you must finish the object with <code>obstack_finish</code> |
| (see <a href="Growing-Objects.html#Growing-Objects">Growing Objects</a>). |
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