如何使用C语言操作Oracle数据库（c oracle数据连接）

如何使用C语言操作Oracle数据库

Oracle是一个非常强大的关系型数据库管理系统，而C语言是一种被广泛使用的编程语言。在本文中，我们将介绍如何使用C语言来操作Oracle数据库。

使用OCI库

Oracle公司提供了OCI库给开发者使用。OCI是Oracle Call Interface的缩写，是一个面向过程的C语言API，可以用于连接、操作和管理Oracle数据库。

下面是一个基本的OCI连接Oracle数据库的示例：

#include 
#include 
#include 
void checkerr(errhp, status)
OCIError *errhp;
sword status;
{
    text errbuf[512];
    sb4 errcode = 0;
    OCIErrorGet((dvoid *)errhp, (ub4)1, (text *)NULL, &errcode,
        errbuf, (ub4)sizeof(errbuf), OCI_HTYPE_ERROR);
    printf("Error occurred: %.*s\n", 512, errbuf);
    exit(1);
}

int mn()
{
    OCIEnv *envhp;
    OCIError *errhp;
    OCIServer *srvhp;
    OCISession *sessionhp;
    OCISvcCtx *svchp;
    sword status;
    OCIInitialize(OCI_DEFAULT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t))0,
        (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *))0);
    OCIEnvInit(&envhp, OCI_DEFAULT, 0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&errhp, OCI_HTYPE_ERROR,
        (size_t)0, (dvoid **)0);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&srvhp, OCI_HTYPE_SERVER,
        (size_t)0, (dvoid **)0);
    status = OCIServerAttach(srvhp, errhp, (text *)"dbname", (sb4)strlen("dbname"),
        OCI_DEFAULT);
    if (status != OCI_SUCCESS)
        checkerr(errhp, status);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&svchp, OCI_HTYPE_SVCCTX,
        (size_t)0, (dvoid **)0);
    OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)srvhp, (ub4)0,
        OCI_ATTR_SERVER, errhp);
    OCIHandleAlloc((dvoid *)envhp, (dvoid **)&sessionhp, OCI_HTYPE_SESSION,
        (size_t)0, (dvoid **)0);
    OCIAttrSet((dvoid *)sessionhp, OCI_HTYPE_SESSION, (dvoid *)"username",
        (ub4)strlen("username"), OCI_ATTR_USERNAME, errhp);
    OCIAttrSet((dvoid *)sessionhp, OCI_HTYPE_SESSION, (dvoid *)"password",
        (ub4)strlen("password"), OCI_ATTR_PASSWORD, errhp);
    status = OCISessionBegin(svchp, errhp, sessionhp, OCI_CRED_RDBMS, OCI_DEFAULT);
    if (status != OCI_SUCCESS)
        checkerr(errhp, status);
    OCIAttrSet((dvoid *)svchp, OCI_HTYPE_SVCCTX, (dvoid *)sessionhp,
        (ub4)0, OCI_ATTR_SESSION, errhp);
    // use the database here...

    OCIHandleFree((dvoid *)sessionhp, OCI_HTYPE_SESSION);
    OCIHandleFree((dvoid *)svchp, OCI_HTYPE_SVCCTX);
    OCIServerDetach(srvhp, errhp, OCI_DEFAULT);
    OCIHandleFree((dvoid *)srvhp, OCI_HTYPE_SERVER);
    OCIHandleFree((dvoid *)errhp, OCI_HTYPE_ERROR);
    OCIEnvCleanup((dvoid *)envhp);
    return 0;
}

以上代码为连接到名为`dbname`的Oracle数据库示例。将示例代码复制并以`test.c`命名，使用以下命令编译：

gcc -o test test.c -I/usr/include/oracle/11.2/client64 -L/usr/lib/oracle/11.2/client64/lib -lclntsh

OCI包含了大量的API可供调用，包括SQL语法、数据类型转换和数据提取等。通过调用`OCIStmtExecute()`和`OCIStmtFetch()`函数，可以轻松地进行SQL查询。

例如，以下代码将从数据库中查询表`employees`中所有员工的名字和雇佣日期，并将结果打印出来：

OCIStmt *stmthp;
OCIParam *colhp;
text *name = NULL;
text *date = NULL;
ub2 name_len = 0;
ub2 date_len = 0;
int i;
OCIHandleAlloc((dvoid *)envhp, (dvoid **)&stmthp, OCI_HTYPE_STMT,
    (size_t)0, (dvoid **)0);
status = OCIStmtPrepare(stmthp, errhp,
    (text *)"SELECT employee_name, hire_date FROM employees", (ub4)strlen("SELECT employee_name, hire_date FROM employees"),
    OCI_NTV_SYNTAX, OCI_DEFAULT);
if (status != OCI_SUCCESS)
    checkerr(errhp, status);
status = OCIStmtExecute(svchp, stmthp, errhp, (ub4)0, (ub4)0, (CONST OCISnapshot *)NULL,
    (OCISnapshot *)NULL, OCI_DEFAULT);
if (status != OCI_SUCCESS && status != OCI_NO_DATA)
    checkerr(errhp, status);
status = OCIStmtFetch(stmthp, errhp, (ub4)1, OCI_FETCH_NEXT, OCI_DEFAULT);
while (status != OCI_NO_DATA)
{
    for (i = 1; i 
    {
        status = OCIParamGet(stmthp, OCI_HTYPE_STMT, errhp,
            (dvoid **)&colhp, (ub4)i);
        if (status != OCI_SUCCESS)
            checkerr(errhp, status);
        status = OCIAttrGet((dvoid *)colhp, OCI_DTYPE_PARAM,
            (dvoid **)&name, (ub4 *)&name_len, OCI_ATTR_NAME, errhp);
        if (status != OCI_SUCCESS)
            checkerr(errhp, status);
        status = OCIAttrGet((dvoid *)colhp, OCI_DTYPE_PARAM,
            (dvoid **)&date, (ub4 *)&date_len, OCI_ATTR_NAME, errhp);
        if (status != OCI_SUCCESS)
            checkerr(errhp, status);
        printf("%.*s=%.*s\n", name_len, name, date_len, date);
    }
    status = OCIStmtFetch(stmthp, errhp, (ub4)1, OCI_FETCH_NEXT, OCI_DEFAULT);
}
OCIHandleFree((dvoid *)stmthp, OCI_HTYPE_STMT);

本次查询结果将会以以下形式打印：

employee_name=John Doe
hire_date=2019-01-01
employee_name=Jane Smith
hire_date=2019-02-01

总结

本文介绍了使用C语言连接和操作Oracle数据库的基本方法。通过OCI库，可以轻松地连接到Oracle数据库、进行SQL查询和数据提取等操作。在应用程序开发过程中，使用OCI库可以为开发者带来更大的灵活性和控制性。