key value数据对于C结构的处理

在前面的文章中阐述了key value数据库写入记录等。但是在处理C结构体的时候，通常需要特殊处理一下。

对于数据的写入通常为memcpy的方式，将一段内存的信息直接进行写入。我们以Berkeley DB为例：

http://download.oracle.com/docs/cd/E17076_02/html/gsg/C/cstructs.html

1.结构体中没有含指针

#include <db.h>#include <string.h>typedef struct my_struct { int id; char familiar_name[MAXLINE]; /* Some suitably large value */ char surname[MAXLINE];} MY_STRUCT;...DBT key, data;DB *my_database;MY_STRUCT user;char *fname = "David";char *sname = "Rider";/* Database open omitted for clarity */user.id = 1;strncpy(user.familiar_name, fname, strlen(fname)+1);strncpy(user.surname, sname, strlen(sname)+1);/* Zero out the DBTs before using them. */memset(&key, 0, sizeof(DBT));memset(&data, 0, sizeof(DBT));key.data = &(user.id);key.size = sizeof(int);data.data = &user;data.size = sizeof(MY_STRUCT); my_database->put(my_database, NULL, &key, &data, DB_NOOVERWRITE);

可以直接按照字符串的方式写入。

2.含有指针的结构体

将指针指向的分配内存，都统一进行malloc分配。组成统一的一段内存信息。

#include <db.h>#include <string.h>#include <stdlib.h>typedef struct my_struct { int id; char *familiar_name; char *surname;} MY_STRUCT;...DBT key, data;DB *my_database;MY_STRUCT user;int buffsize, bufflen;char fname[ ] = "Pete";char sname[10];char *databuff;strncpy(sname, "Oar", strlen("Oar")+1);/* Database open omitted for clarity */user.id = 1;user.familiar_name = fname;user.surname = sname;/* Some of the structure's data is on the stack, and * some is on the heap. To store this structure's data, we * need to marshall it -- pack it all into a single location * in memory. *//* Get the buffer */buffsize = sizeof(int) + (strlen(user.familiar_name) + strlen(user.surname) + 2);databuff = malloc(buffsize);memset(databuff, 0, buffsize);/* copy everything to the buffer */memcpy(databuff, &(user.id), sizeof(int));bufflen = sizeof(int);memcpy(databuff + bufflen, user.familiar_name, strlen(user.familiar_name) + 1);bufflen += strlen(user.familiar_name) + 1;memcpy(databuff + bufflen, user.surname, strlen(user.surname) + 1);bufflen += strlen(user.surname) + 1;/* Now store it *//* Zero out the DBTs before using them. */memset(&key, 0, sizeof(DBT));memset(&data, 0, sizeof(DBT));key.data = &(user.id);key.size = sizeof(int);data.data = databuff;data.size = bufflen;my_database->put(my_database, NULL, &key, &data, DB_NOOVERWRITE);free(sname);free(databuff);

3.总结

 对于key value数据库中，如果写入的结构体过于复杂，处理并不方便，但是不用指针，基本不可能。

还需要对于这方面进行一个研究。