Dynamic Output - The GNU C Library

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#### 12.12.8 Dynamically Allocating Formatted Output

The functions in this section do formatted output and place the results in dynamically allocated memory.

— Function: int asprintf (char **ptr, const char *template, ...)

> This function is similar to `sprintf`, except that it dynamically allocates a string (as with `malloc`; see Unconstrained Allocation) to hold the output, instead of putting the output in a buffer you allocate in advance. The ptr argument should be the address of a `char *` object, and a successful call to `asprintf` stores a pointer to the newly allocated string at that location.

> 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.

> Here is how to use `asprintf` to get the same result as the `snprintf` example, but more easily:

>               /* Construct a message describing the value of a variable
>                  whose name is name and whose value is value. */
>               char *
>               make_message (char *name, char *value)
>               {
>                 char *result;
>                 if (asprintf (&result, "value of %s is %s", name, value) < 0)
>                   return NULL;
>                 return result;
>               }

— Function: int obstack_printf (struct obstack *obstack, const char *template, ...)

> This function is similar to `asprintf`, except that it uses the obstack obstack to allocate the space. See Obstacks.

> The characters are written onto the end of the current object. To get at them, you must finish the object with `obstack_finish` (see Growing Objects).