vasprintf的实现

有些系统，例如AIX，没有vasprintf和asprintf ，如果是做porting，有时需要写一个简单的代替。

代码如下：

 #if !defined(HAVE_VASPRINTF)
 #if defined(WINDOWS)
 int
 vasprintf (char **ptr, const char *format, va_list ap)
 {
   int len; 

   len = _vscprintf_p (format, ap) + ;
   *ptr = (char *) malloc (len * sizeof (char));
   if (!*ptr)
     {
       return -;
     } 

   return _vsprintf_p (*ptr, len, format, ap);
 }
 #else
 int
 vasprintf (char **ptr, const char *format, va_list ap)
 {
   va_list ap_copy; 

   /* Make sure it is determinate, despite manuals indicating otherwise */
   *ptr = ; 

   va_copy(ap_copy, ap);
   int count = vsnprintf(NULL, , format, ap);
   if (count >= )
         {
           char* buffer = malloc(count + );
           if (buffer != NULL)
                 {
                   count = vsnprintf(buffer, count + , format, ap_copy);
                   if (count < )
                         free(buffer);
                   else
                         *ptr = buffer;
                 }
         }
   va_end(ap_copy); 

   return count; 

 }
 #endif
 #endif /* !HAVE_VASPRINTF */ 

 #if !defined(HAVE_ASPRINTF)
 int
 asprintf (char **ptr, const char *format, ...)
 {
   va_list ap;
   int ret; 

   *ptr = NULL; 

   va_start (ap, format);
   ret = vasprintf (ptr, format, ap);
   va_end (ap); 

   return ret;
 }
 #endif /* !HAVE_ASPRINTF */ 

下面是一个完整的例子：

 #include <stdio.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h> 

 int
 myvasprintf (char **ptr, const char *format, va_list ap)
 {
   va_list ap_copy; 

   /* Make sure it is determinate, despite manuals indicating otherwise */
   *ptr = ; 

   va_copy(ap_copy, ap);
   int count = vsnprintf(NULL, , format, ap);
   if (count >= )
     {
       char* buffer = malloc(count + );
       if (buffer != NULL)
         {
           count = vsnprintf(buffer, count + , format, ap_copy);
           if (count < )
             free(buffer);
           else
             *ptr = buffer;
         }
     }
   va_end(ap_copy); 

   return count; 

 } 

 void
 print_warning (char **buffer, const char *fmt, ...)
 {
   va_list ap;
   va_start (ap, fmt);
   myvasprintf (buffer, fmt, ap);
   va_end (ap);
 } 

 int main()
 {
   char *buffer;
   int a = ;
   int b = ;
   print_warning(&buffer, "hello, world, %d * %d = %d, %s\n", a, b, a * b, "finished!!" ); 

   printf(buffer);
   return ;
 } 

上述代码的执行结果如下：

hello, world, 99999 * 9 = 899991, finished!!