我正在尝试使用berkeley DB来存储和获取简单的密钥/数据对,但这并不像我所期望的那样工作。
我创建了一个函数(putdb())将一个密钥/数据对放入数据库,并创建了另一个函数(getdb())来检索这一对。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <db.h>
DB *dbp;
void opendb(void)
{
        int ret;
        if ((ret = db_create(&dbp, NULL, 0)) != 0)
                exit(EXIT_FAILURE);
        if ((ret = dbp->open(dbp, NULL, "db.db", NULL,DB_BTREE, DB_CREATE, 0664)) != 0)
                exit(EXIT_FAILURE);
}


void putdb(const char *key, const char *value)
{
    DBT keyValue, dataValue;
    memset(&keyValue, 0, sizeof(keyValue));
    memset(&dataValue, 0, sizeof(dataValue));

    keyValue.size = sizeof(key);
    dataValue.size = sizeof(value);

    keyValue.data = malloc(keyValue.size);
    strcpy(keyValue.data,key);

    dataValue.data = malloc(dataValue.size);
    strcpy(dataValue.data,value);

    if ((ret = dbp->put(dbp, NULL, &keyValue, &dataValue, 0)) == 0)
            printf("db: %s: key stored.\n", (char *)keyValue.data);
    else {
            dbp->err(dbp, ret, "DB->put");
    }
    dbp->sync(dbp, 0);
}

void getdb(const char *key,const char *value)
{
    DBT keyValue, dataValue;
    memset(&keyValue, 0, sizeof(keyValue));
    memset(&dataValue, 0, sizeof(dataValue));

    keyValue.size = sizeof(key);
    dataValue.size = sizeof(value);

    keyValue.data = malloc(keyValue.size);
    strcpy(keyValue.data,key);

    dataValue.data = malloc(dataValue.size);
    strcpy(dataValue.data,value);

    if ((ret = dbp->get(dbp, NULL, &keyValue, &dataValue, 0)) == 0)
            printf("db: %s: key retrieved: data was %s.\n",
                (char *)keyValue.data, (char *)dataValue.data);
    else {
            dbp->err(dbp, ret, "DB->get");
    }
}
void closedb(void)
{
    dbp->close(dbp, 0);
    //TODO : error code return check
}

以及主文件:
int main()
{
    opendb();
    putdb("toto","titi");
    getdb("toto","titi");
    closedb();
 }

我得到:
db: toto: key stored.
DB->get: BDB0073 DB_NOTFOUND: No matching key/data pair found

你能解释一下原因吗?
请注意,如果我更改了主要功能:
int main()
{
    opendb();
    putdb("toto","titi");
    closedb();
    opendb();
    getdb("toto","titi");
    closedb();
}

那就行了!:
db: toto: key stored.
db: toto: key retrieved: data was titi.

最佳答案

你从教程中抄得太多了。它们可以使用sizeof("a string"),但您必须同时在strlen(key)putdb中使用getdb

keyValue.size = strlen(key);
dataValue.size = strlen(value);

关于c - Berkeley DB在不关闭数据库的情况下无法放置然后访问数据,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/39312527/

10-11 22:57
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