相关疑难解决方法(0)

我正在阅读这个页面 http://dev.mysql.com/doc/refman/5.0/en/mysql-fetch-row.html 有一行

printf("[%.*s] ", (int) lengths[i],
              row[i] ? row[i] : "NULL");

来自代码

    MYSQL_ROW row;
unsigned int num_fields;
unsigned int i;

num_fields = mysql_num_fields(result);
while ((row = mysql_fetch_row(result)))
{
   unsigned long *lengths;
   lengths = mysql_fetch_lengths(result);
   for(i = 0; i < num_fields; i++)
   {
       printf("[%.*s] ", (int) lengths[i],
              row[i] ? row[i] : "NULL");
   }
   printf("\n");

}

[%.*s]那段代码意味着什么？

这对许多人来说可能是一个非常基本的问题,但我无法理解%.*s在做什么？

void substring(int i, int j, char *ch) 
{
      printf("The substring is: %.*s\n", j - i, &ch[i]); 
      //what is %.*s doing?
}