用c语言根据可变参数合成字符串的实现代码

char *xm_vsprintf_ex(int len, char *fmt, ... );

int main(int argc, char *argv[])
{
 char *ptr;
 ptr = xm_vsprintf_ex(100, "%s-%s-%s", "lias", "dzq", "lvo");
 printf("%s\n", ptr);
 free(ptr);

 return 0;
}

char *xm_vsprintf_ex(int len, char *fmt, ... )
{
 va_list ap;
 char *ptr;

 ptr = (char *)malloc(len * sizeof(char));
 if(ptr == NULL)
 {
  fprintf(stderr, "malloc failed\n");
  return NULL;
 }
 memset(ptr, 0, len);

 va_start(ap, fmt);
 vsprintf(ptr, fmt, ap);
 va_end(ap);

 ptr[len-1] = '\0';

 return ptr;
}