/
db.c
142 lines (114 loc) · 2.72 KB
/
db.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
typedef struct
{
// primary key
unsigned int key;
// first name
char fname[16];
// last name
char lname[16];
// age
unsigned int age;
} person_record;
int update_record(char *filename, int append_flag)
{
int fd;
if(append_flag == 0)
fd = open(filename, O_CREAT | O_RDWR, 0644);
else
fd = open(filename, O_CREAT | O_RDWR | O_APPEND, 0644);
if(fd == -1)
perror("open_record");
return fd;
}
void close_record(int fd)
{
close(fd);
}
int insert_record(int fd, person_record *record)
{
int ret;
ret = write(fd, record, sizeof(person_record));
return ret;
}
int get_record(int fd, person_record *record, int key)
{
int ret;
while ((ret = read(fd, record, sizeof(person_record))) != -1)
{
if(ret == 0)
{
memset(record, 0, sizeof(person_record));
break;
return ret;
}
else if(key == record->key)
return ret;
}
memset(record, 0, sizeof(person_record));
return ret;
}
int delete_record(int fd, int key)
{
int ret;
person_record record;
off_t pos;
pos = lseek(fd, 0, SEEK_SET);
while ((ret = read(fd, &record, sizeof(person_record))) != -1)
{
if(ret == 0)
{
return ret;
}
else if(key == record.key) {
lseek(fd, pos, SEEK_SET);
record.key = 0;
ret = write(fd, &record, sizeof(person_record));
return ret;
}
pos = lseek(fd, 0, SEEK_CUR);
}
return ret;
}
int main(int argc, char *argv[])
{
int fd;
person_record rec;
/* fd = open_record("data1"); */
if(argc > 1)
{
// insert data
if(argc > 5 && !strcmp(argv[1], "insert"))
{
fd = update_record("data1", 1);
rec.key = atoi(argv[2]);
strcpy(rec.fname, argv[3]);
strcpy(rec.lname, argv[4]);
rec.age = atoi(argv[5]);
insert_record(fd, &rec);
}
/* delete data */
if(argc > 2 && !strcmp(argv[1], "delete"))
{
fd = update_record("data1", 0);
delete_record(fd, atoi(argv[2]));
}
/* print data */
if(argc > 2 && !strcmp(argv[1], "print"))
{
fd = update_record("data1", 1);
get_record(fd, &rec, atoi(argv[2]));
printf("key = %d\n", rec.key);
printf("First = %s\n", rec.fname);
printf("Last = %s\n", rec.lname);
printf("Age = %d\n", rec.age);
}
}
close_record(fd);
return 0;
}