1 /*
2 * pANS stdio -- freopen
3 */
4 #include "iolib.h"
5 /*
6 * Open the named file with the given mode, using the given FILE
7 * Legal modes are given below, `additional characters may follow these sequences':
8 * r rb open to read
9 * w wb open to write, truncating
10 * a ab open to write positioned at eof, creating if non-existant
11 * r+ r+b rb+ open to read and write, creating if non-existant
12 * w+ w+b wb+ open to read and write, truncating
13 * a+ a+b ab+ open to read and write, positioned at eof, creating if non-existant.
14 */
freopen(const char * name,const char * mode,FILE * f)15 FILE *freopen(const char *name, const char *mode, FILE *f){
16 int m;
17
18 if(f->state!=CLOSED){
19 fclose(f);
20 /* premature; fall through and see what happens */
21 /* f->state=OPEN; */
22 }
23
24 m = *mode++;
25 if(m == 0)
26 return NULL;
27 if(*mode == 'b')
28 mode++;
29 switch(m){
30 default:
31 return NULL;
32 case 'r':
33 f->fd=open(name, (*mode == '+'? O_RDWR: O_RDONLY));
34 break;
35 case 'w':
36 f->fd=creat(name, 0666); /* implicitly O_WRONLY */
37 /* for O_RDWR, have to creat, close, open */
38 if(*mode == '+' && f->fd >= 0) {
39 close(f->fd);
40 f->fd=open(name, O_RDWR);
41 }
42 break;
43 case 'a':
44 f->fd=open(name, (*mode == '+'? O_RDWR: O_WRONLY));
45 if(f->fd<0) {
46 f->fd=creat(name, 0666);
47 /* for O_RDWR, have to creat, close, open */
48 if(*mode == '+' && f->fd >= 0) {
49 close(f->fd);
50 f->fd=open(name, O_RDWR);
51 }
52 }
53 lseek(f->fd, 0L, 2);
54 break;
55 }
56
57 if(f->fd==-1)
58 return NULL;
59 f->flags=(mode[0]=='a')? APPEND : 0;
60 f->state=OPEN;
61 f->buf=0;
62 f->rp=0;
63 f->wp=0;
64 f->lp=0;
65 return f;
66 }
67