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：

 

 1 #if !defined(HAVE_VASPRINTF) 

 2 #if defined(WINDOWS) 

 3 int 

 4 vasprintf (char **ptr, const char *format, va_list ap) 

 5 { 

 6   int len; 

 7  

 8   len = _vscprintf_p (format, ap) + 1; 

 9   *ptr = (char *) malloc (len * sizeof (char)); 

10   if (!*ptr) 

11     { 

12       return -1; 

13     } 

14  

15   return _vsprintf_p (*ptr, len, format, ap); 

16 } 

17 #else 

18 int 

19 vasprintf (char **ptr, const char *format, va_list ap) 

20 { 

21   va_list ap_copy; 

22  

23   /* Make sure it is determinate, despite manuals indicating otherwise */ 

24   *ptr = 0; 

25  

26   va_copy(ap_copy, ap); 

27   int count = vsnprintf(NULL, 0, format, ap); 

28   if (count >= 0) 

29         { 

30           char* buffer = malloc(count + 1); 

31           if (buffer != NULL) 

32                 { 

33                   count = vsnprintf(buffer, count + 1, format, ap_copy); 

34                   if (count < 0) 

35                         free(buffer); 

36                   else 

37                         *ptr = buffer; 

38                 } 

39         } 

40   va_end(ap_copy); 

41  

42   return count; 

43  

44 } 

45 #endif 

46 #endif /* !HAVE_VASPRINTF */ 

47  

48 #if !defined(HAVE_ASPRINTF) 

49 int 

50 asprintf (char **ptr, const char *format, ...) 

51 { 

52   va_list ap; 

53   int ret; 

54  

55   *ptr = NULL; 

56  

57   va_start (ap, format); 

58   ret = vasprintf (ptr, format, ap); 

59   va_end (ap); 

60  

61   return ret; 

62 } 

63 #endif /* !HAVE_ASPRINTF */ 

 

下面是一个完整的例子：

 

 1 #include <stdio.h> 

 2 #include <stdarg.h> 

 3 #include <stdlib.h> 

 4 #include <string.h> 

 5  

 6 int 

 7 myvasprintf (char **ptr, const char *format, va_list ap) 

 8 { 

 9   va_list ap_copy; 

10  

11   /* Make sure it is determinate, despite manuals indicating otherwise */ 

12   *ptr = 0; 

13  

14   va_copy(ap_copy, ap); 

15   int count = vsnprintf(NULL, 0, format, ap); 

16   if (count >= 0) 

17     { 

18       char* buffer = malloc(count + 1); 

19       if (buffer != NULL) 

20         { 

21           count = vsnprintf(buffer, count + 1, format, ap_copy); 

22           if (count < 0) 

23             free(buffer); 

24           else 

25             *ptr = buffer; 

26         } 

27     } 

28   va_end(ap_copy); 

29  

30   return count; 

31  

32 } 

33  

34 void 

35 print_warning (char **buffer, const char *fmt, ...) 

36 { 

37   va_list ap; 

38   va_start (ap, fmt); 

39   myvasprintf (buffer, fmt, ap); 

40   va_end (ap); 

41 } 

42  

43 int main() 

44 { 

45   char *buffer; 

46   int a = 99999; 

47   int b = 9; 

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

49  

50   printf(buffer); 

51   return 0; 

52 } 

上述代码的执行结果如下：

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