>>353
typedefがないとstdio.hのFILEの代わりにコンパイラごとに異なった構造体を使う羽目になるよ。
例えば、FILEはこんな構造体の別名になっているかも知れない。
--
struct __sFILE {
unsigned char *_p; /* current position in (some) buffer */
int _r; /* read space left for getc() */
int _w; /* write space left for putc() */
short _flags; /* flags, below; this FILE is free if 0 */
short _file; /* fileno, if Unix descriptor, else -1 */
struct __sbuf _bf; /* the buffer (at least 1 byte, if !NULL) */
int _lbfsize; /* 0 or -_bf._size, for inline putc */

/* separate buffer for long sequences of ungetc() */
struct __sbuf _ub; /* ungetc buffer */
unsigned char *_up; /* saved _p when _p is doing ungetc data */
int _ur; /* saved _r when _r is counting ungetc data */

/* tricks to meet minimum requirements even when malloc() fails */
unsigned char _ubuf[3]; /* guarantee an ungetc() buffer */
unsigned char _nbuf[1]; /* guarantee a getc() buffer */

/* separate buffer for fgetline() when line crosses buffer boundary */
struct __sbuf _lb; /* buffer for fgetline() */

};