C语言查询Oracle数据库中的中文信息（c oracle 查中文）

C语言查询Oracle数据库中的中文信息

一、前言

在实际应用中，C语言的应用非常广泛。而Oracle是目前领先的企业级数据库管理系统，其广泛应用于国内外各大行业。如何在C语言中查询Oracle数据库中的中文信息？接下来将从连接Oracle数据库、设置环境、连接池、查询中文信息等方面进行介绍。

二、连接Oracle数据库

C语言中连接Oracle数据库需要用到Oracle官方提供的OCI(Oracle Call Interface)库。以下是C语言连接Oracle数据库的代码示例：

“`c

#include

#include

#include

#include

// 配置连接信息

char username[] = “username”;

char password[] = “password”;

char dbname[] = “localhost/orcl”;

char dsn[] = “”;

// 初始化OCI环境

OCIEnv *envhp;

(void)OCIEnvCreate(&envhp, OCI_DEFAULT, (dvoid *)0, (dvoid * (*)(dvoid *,size_t))0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *))0, (size_t)0, (dvoid **)0);

// 初始化OCI错误处理器

OCIError *errhp;

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, (size_t)0, (dvoid **)0);

// 初始化Oracle会话

OCISession *authp;

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&authp, OCI_HTYPE_SESSION, (size_t)0, (dvoid **)0);

OCIAttrSet((dvoid *)authp, (ub4)OCI_HTYPE_SESSION, (dvoid *)username, (ub4)strlen((char *)username), OCI_ATTR_USERNAME, errhp);

OCIAttrSet((dvoid *)authp, (ub4)OCI_HTYPE_SESSION, (dvoid *)password, (ub4)strlen((char *)password), OCI_ATTR_PASSWORD, errhp);

OCIAttrSet((dvoid *)authp, (ub4)OCI_HTYPE_SESSION, (dvoid *)dbname, (ub4)strlen((char *)dbname), OCI_ATTR_AUTHENTICATION_DATA, errhp);

// 设置OCI服务器环境句柄

OCIServer *srvhp;

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&srvhp, OCI_HTYPE_SERVER, (size_t)0, (dvoid **)0);

OCIAttrSet((dvoid *)srvhp, (ub4)OCI_HTYPE_SERVER, (dvoid *)&dsn, (ub4)strlen((char *)dsn), OCI_ATTR_SERVER_DNS, errhp);

// 连接Oracle数据库

OCISvcCtx *svchp;

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX, (size_t)0, (dvoid **)0);

OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4)0, OCI_ATTR_SERVER, errhp);

OCIAttrSet((dvoid *)svchp, (ub4)OCI_HTYPE_SVCCTX, (dvoid *)authp, (ub4)0, OCI_ATTR_SESSION, errhp);

// 结束语句

OCITransCommit((OCIExtProcContext *) 0, errhp, OCI_DEFAULT);

OCISessionEnd((OCISvcCtx *)svchp, (OCIError *)errhp, (OCISession *)authp, OCI_DEFAULT);

OCIServerDetach((OCIServer *)srvhp, (OCIError *)errhp, OCI_DEFAULT);

三、设置环境

在连接Oracle数据库之前，需要进行环境设置。以下是C语言设置环境的代码示例：

```c
OCIEnv *envhp;
OCIError *errhp;
OCIHandleAlloc((dvoid *)NULL, (dvoid **)&envhp, OCI_HTYPE_ENV, (size_t)0, (void **)0);
OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, (size_t)0, (void **)0);
OCIEnvInit((OCIEnv **)&envhp, OCI_DEFAULT, (size_t)0, (dvoid **)0);

四、连接池

连接池使得应用能够重用连接对象以减少与数据库服务器的交互次数，从而提高了系统性能。以下是C语言连接池的代码示例：

“`c

OCIEnv *envhp;

OCIError *errhp;

OCIHandleAlloc((dvoid *)NULL, (dvoid **)&envhp, OCI_HTYPE_ENV, (size_t)0, (void **)0);

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR, (size_t)0, (void **)0);

OCIEnvInit((OCIEnv **)&envhp, OCI_DEFAULT, (size_t)0, (dvoid **)0);

int pool_size = 10;

int min_conn = 5;

int max_conn = 20;

int incr_conn = 1;

int timeout = 30;

int stmt_cache_size = 30;

OCIError *errhp;

OCIConnectionPool *poolhp;

OCIHandleAlloc((dvoid *)envhp, (dvoid **)&poolhp, OCI_HTYPE_POOL, (size_t)0, (dvoid **)0);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&pool_size, (ub4)sizeof(pool_size), OCI_ATTR_POOL_MAX, errhp);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&min_conn, (ub4)sizeof(min_conn), OCI_ATTR_MIN, errhp);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&max_conn, (ub4)sizeof(max_conn), OCI_ATTR_MAX, errhp);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&incr_conn, (ub4)sizeof(incr_conn), OCI_ATTR_INCR, errhp);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&timeout, (ub4)sizeof(timeout), OCI_ATTR_TIMEOUT, errhp);

OCIAttrSet((dvoid *)poolhp, OCI_HTYPE_POOL, (dvoid *)&stmt_cache_size, (ub4)sizeof(stmt_cache_size), OCI_ATTR_STMTCACHESIZE, errhp);

五、查询中文信息

查询中文信息需要设置环境，连接Oracle数据库，调用OCILobCopy等函数进行访问。以下是C语言查询中文信息的代码示例：

```c
#include 
#include 
#include 
#include 
void query_lob(OCIEnv *envhp, OCISvcCtx *svchp, OCIError *errhp)
{
    // 执行SQL语句
    OCIStmt *stmt;
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmt, OCI_HTYPE_STMT, (size_t)0, (dvoid **)0);
    char *sql = "SELECT * FROM table WHERE id = ?";
    OCIStmtPrepare(stmt, errhp, (unsigned char *)sql, (ub4)strlen(sql), OCI_NTV_SYNTAX, OCI_DEFAULT);
    int id = 123;
    OCIBindByPos(stmt, (OCIBind **)&id, errhp, (ub4)sizeof(id), SQLT_INT, (dvoid *)0, (ub2 *)0, (ub2 *)0, (ub4)0, (ub4 *)0, OCI_DEFAULT);

    OCIStmtExecute(svchp, stmt, errhp, (ub4)1, (ub4)0, (OCISnapshot *)NULL, (OCISnapshot *)NULL, OCI_DEFAULT);

    // 获取LOB字段
    OCILobLocator *lob_loc;
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&lob_loc, (ub4)OCI_DTYPE_LOB, (size_t)0, (dvoid **)0);
    OCIParamGet(stmt, OCI_HTYPE_STMT, errhp, (void **)&lob_loc, (ub4)1);
    // 处理LOB字段
    char buffer[1024];
    int offset = 0;
    int len = 1024;
    int res = OCILobRead(svchp, errhp, lob_loc, (ub4 *)&len, (ub4)offset, (void *)buffer, (ub4)1024, (dvoid *)0, (sb4 (*)(void *, void *, ub4, ub1))0, (ub2)0, (ub1)SQLCS_IMPLICIT);
    while(res != OCI_SUCCESS_WITH_INFO && res != OCI_NO_DATA)
    {
        printf("%s", buffer);
        offset += 1024;
        len = 1024;
        res = OCILobRead(svchp, errhp, lob_loc, (ub4 *)&len, (ub4)offset, (void *)buffer, (ub4)1024, (dvoid *)0, (sb4 (*)(void