1 /* 2 * fopen.c 3 */ 4 5 #include <stdio.h> 6 #include <unistd.h> 7 #include <fcntl.h> 8 fopen(const char * file,const char * mode)9FILE *fopen(const char *file, const char *mode) 10 { 11 int flags = O_RDONLY; 12 int plus = 0; 13 int fd; 14 15 while (*mode) { 16 switch (*mode) { 17 case 'r': 18 flags = O_RDONLY; 19 break; 20 case 'w': 21 flags = O_WRONLY | O_CREAT | O_TRUNC; 22 break; 23 case 'a': 24 flags = O_WRONLY | O_CREAT | O_APPEND; 25 break; 26 case '+': 27 plus = 1; 28 break; 29 } 30 mode++; 31 } 32 33 if (plus) { 34 flags = (flags & ~(O_RDONLY | O_WRONLY)) | O_RDWR; 35 } 36 37 fd = open(file, flags, 0666); 38 39 if (fd < 0) 40 return NULL; 41 else 42 return fdopen(fd, mode); 43 } 44