Question

I’m wondering if such a function exists:

void str_realloc_and_concat(char *str, const char *format, ...)

This function would take a char *str (allocated or NULL), and append to it *format.
I’m looking for something like a sprintf with realocation, strcpy and concatenation.

Does it exist or do I have to code it? Thanks for your inputs.

Update
The library has to be used on a embedded device so I don’t want to use GNU extensions, since I’m not sure I’ll have them.

Answer 1

I decided to go with this. Hope it will help.

/**
 * Reallocate a string and concatenate it with a formatted string.
 * The src string has to be allocated by malloc/calloc.
 * @param src Pointer to the original string
 * @param format Format string
 * @param ... Arguments that are to be formatted
 */
char *strcatf(char *src, const char *format, ...)
{
  va_list ap, cp;
  int format_length;
  size_t translation_length;
  char *dest;

  if (NULL == src) {
    return NULL;
  }

  va_start(ap, format);
  va_copy(cp, ap);

  translation_length = strlen(src);
  format_length = vsnprintf(NULL, 0, format, cp);
  if ((dest = realloc(src, (translation_length + format_length + 1) * sizeof(char))) == NULL) {
    free(src);
  } else {
    vsprintf(&(dest)[translation_length], format, ap);
  }
  va_end(ap);
  va_end(cp);
  return dest;
}