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请教Berkeley DB的游标操作

时间：2010-08-29

来源：互联网

网上翻了下，没有找到完整的测试代码，即使有c的api相关介绍也是列了一下流程，贴了少许代码，测试下不行。郁闷啊，请大家帮我看看。

版本是libdb4.6-dev

测试代码如下：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <db.h>
#define DBNAME "test.db"
typedef struct emp {
int empid;
char lastname[50];
char firstname[50];
float salary;
} emp_t;
DB *openDB(const char *dbFile)
{
DB *dbp = NULL;
int ret = 0;
ret = db_create(&dbp, NULL, 0);
if (ret != 0) {
printf("ERROR: %s\n",db_strerror(ret));
return NULL;
}
ret = dbp->open(dbp, NULL, dbFile, NULL, DB_BTREE, DB_CREATE, 0);
if (ret != 0) {
printf("ERROR: %s\n",db_strerror(ret));
return NULL;
}
return dbp;
}
int main(int argc, char* argv[])
{
DB *dbp;
DBC *cursor;
int ret = 0;
DBT key, data;
emp_t emp;
if ((dbp = openDB(DBNAME)) == NULL) {
printf("open failed\n");
return 1;
}
/* insert */
while (1) {
printf("Enter Employee ID: ");
scanf("%d", &emp.empid);
if (emp.empid == 0)
break;
printf("Enter Last name: ");
scanf("%s", emp.lastname);
printf("Enter first name: ");
scanf("%s", emp.firstname);
printf("Enter Salary: ");
scanf("%f", &emp.salary);
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
key.data = &(emp.empid);
key.size = sizeof(emp.empid);
data.data = &emp;
data.size = sizeof(emp_t);
ret = dbp->put(dbp, NULL, &key, &data, DB_NOOVERWRITE);
if (ret != 0) {
printf("Employee ID exists\n");
continue;
}
}
/* search */
while (1) {
printf("Enter Employee ID you wana search: ");
scanf("%d", &emp.empid);
if (emp.empid == 0)
break;
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
key.data = &(emp.empid);
key.size = sizeof(emp.empid);
data.data = &emp;
data.ulen = sizeof(emp_t);
data.flags = DB_DBT_USERMEM;
ret = dbp->get(dbp, NULL, &key, &data, 0);
if (ret != 0) {
printf("Employee ID doesn't exist\n");
} else {
printf(" Employee: %d - %s, %s\n Salary: $%.2lf\n", emp.empid, emp.lastname, emp.firstname, emp.salary);
}
}
/* delete */
while (1) {
printf("Enter Employee ID you wana delete: ");
scanf("%d", &emp.empid);
if (emp.empid == 0)
break;
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
key.data = &(emp.empid);
key.size = sizeof(emp.empid);
ret = dbp->del(dbp, NULL, &key, 0);
if (ret != 0) {
if (ret == DB_NOTFOUND)
printf("Employee ID doesn't exist\n");
} else {
printf(" Employee %d deleted.\n", emp.empid);
}
}
/* cursor */
ret = dbp->cursor(dbp, NULL, &cursor, 0);
if (ret != 0) {
printf("ERROR: %s\n",db_strerror(ret));
return 1;
}
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
data.data = &emp;
data.size = sizeof(emp);
/* data.flags = DB_DBT_USERMEM; */
while ((ret = cursor->get(cursor, &key, &data, DB_NEXT)) == 0) {
printf("ret = %d\n", ret);
printf("%d - %s, %s $%.2lf\n", emp.empid, emp.lastname, emp.firstname, emp.salary);
memset(&key, 0, sizeof(DBT));
memset(&data, 0, sizeof(DBT));
}
if (ret < 0) {
printf("ERROR: %s\n",db_strerror(ret));
}
cursor->close(cursor);
dbp->close(dbp, 0);
return 0;
}

复制代码

gcc -Wall test.c -ldb即可
首先提示你输入一些数据，id, 用户名,薪水。然后是测试查找，删除，这些都是没有问题。输入0可以退出一个测试项目
关键是下面的游标，加上DB_DBT_USERMEM，还报“ERROR: DB_BUFFER_SMALL: User memory too small for return value”
游标还不能打出数据，请教到底何处写错了？