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) + 1; 
  *ptr = (char *) malloc (len * sizeof (char)); 
  if (!*ptr) 
    { 
      return -1; 
    } 
 
  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 = 0; 
 
  va_copy(ap_copy, ap); 
  int count = vsnprintf(NULL, 0, format, ap); 
  if (count >= 0) 
        { 
          char* buffer = malloc(count + 1); 
          if (buffer != NULL) 
                { 
                  count = vsnprintf(buffer, count + 1, format, ap_copy); 
                  if (count < 0) 
                        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 = 0; 
 
  va_copy(ap_copy, ap); 
  int count = vsnprintf(NULL, 0, format, ap); 
  if (count >= 0) 
    { 
      char* buffer = malloc(count + 1); 
      if (buffer != NULL) 
        { 
          count = vsnprintf(buffer, count + 1, format, ap_copy); 
          if (count < 0) 
            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 = 99999; 
  int b = 9; 
  print_warning(&buffer, "hello, world, %d * %d = %d, %s
", a, b, a * b, "finished!!" ); 
 
  printf(buffer); 
  return 0; 
} 

上述代码的执行结果如下：

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