C连接Oracle的demo

下面是一个C语言连接Oracle数据库的简单示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <oci.h>

#define MAX_COL_LENGTH 256

int main()
{
    OCIEnv *envhp;
    OCIError *errhp;
    OCISvcCtx *svchp;
    OCIStmt *stmthp;
    OCIDefine *defnp;
    OCIDateTime *datehp;
    OCIBind *bindhp;
    OCILobLocator *lobhp;
    OCINumber *numhp;
    OCITrans *transhp;
    OCIServer *srvhp;
    
    char *username = "your_username";
    char *password = "your_password";
    char *dbname = "your_database_name";
    char *query = "SELECT * FROM your_table";
    
    sword status;
    int col_count, i, j;
    char col_name[MAX_COL_LENGTH];
    char col_value[MAX_COL_LENGTH];
    ub2 col_type;
    ub4 col_length;
    
    /* 初始化OCI环境 */
    OCIEnvCreate(&envhp, OCI_DEFAULT, 0, 0, 0, 0, 0, 0);
    OCIHandleAlloc(envhp, (void **)&errhp, OCI_HTYPE_ERROR, 0, 0);
    OCIHandleAlloc(envhp, (void **)&srvhp, OCI_HTYPE_SERVER, 0, 0);
    OCIHandleAlloc(envhp, (void **)&svchp, OCI_HTYPE_SVCCTX, 0, 0);
    OCIHandleAlloc(envhp, (void **)&stmthp, OCI_HTYPE_STMT, 0, 0);
    OCIHandleAlloc(envhp, (void **)&transhp, OCI_HTYPE_TRANS, 0, 0);
    
    /* 连接Oracle数据库 */
    OCIServerAttach(srvhp, errhp, (text *)dbname, strlen(dbname), OCI_DEFAULT);
    OCIAttrSet(svchp, OCI_HTYPE_SVCCTX, srvhp, 0, OCI_ATTR_SERVER, errhp);
    OCIHandleAlloc(envhp, (void **)&bindhp, OCI_HTYPE_BIND, 0, 0);
    OCIHandleAlloc(envhp, (void **)&defnp, OCI_HTYPE_DEFINE, 0, 0);
    OCIAttrSet((void *)stmthp, OCI_HTYPE_STMT, (void *)svchp, 0, OCI_ATTR_SVCCTX, errhp);
    OCILogon2(envhp, errhp, &svchp, (text *)username, strlen(username), (text *)password, strlen(password), (text *)dbname, strlen(dbname), OCI_DEFAULT);

    /* 开始事务 */
    OCIAttrSet((void *)svchp, OCI_HTYPE_SVCCTX, (void *)transhp, 0, OCI_ATTR_TRANS, errhp);
    OCITransStart(svchp, errhp, 2, OCI_TRANS_NEW);
    
    /* 执行SQL查询 */
    OCIStmtPrepare(stmthp, errhp, (text *)query, strlen(query), OCI_NTV_SYNTAX, OCI_DEFAULT);
    OCIStmtExecute(svchp, stmthp, errhp, 0, 0, 0, 0, OCI_DEFAULT);
    
    /* 获取查询结果列数 */
    OCIAttrGet(stmthp, OCI_HTYPE_STMT, &col_count, 0, OCI_ATTR_PARAM_COUNT, errhp);
    
    /* 输出查询结果 */
    for (i = 1; i <= col_count; i++) {
        OCIParamGet(stmthp, OCI_HTYPE_STMT, errhp, (void **)&defnp, i);
        OCIAttrGet(defnp, OCI_DTYPE_PARAM, &col_name, 0, OCI_ATTR_NAME, errhp);
        OCIAttrGet(defnp, OCI_DTYPE_PARAM, &col_type, 0, OCI_ATTR_DATA_TYPE, errhp);
        OCIAttrGet(defnp, OCI_DTYPE_PARAM, &col_length, 0, OCI_ATTR_DATA_SIZE, errhp);
        printf("%s\t", col_name);
    }
    printf("\n");
    
    while ((status = OCIStmtFetch(stmthp, errhp, 1, OCI_FETCH_NEXT, OCI_DEFAULT)) == OCI_SUCCESS) {
        for (i = 1; i <= col_count; i++) {
            OCIParamGet(stmthp, OCI_HTYPE_STMT, errhp, (void **)&defnp, i);
            OCIAttrGet(defnp, OCI_DTYPE_PARAM, &col_type, 0, OCI_ATTR_DATA_TYPE, errhp);
            OCIAttrGet(defnp, OCI_DTYPE_PARAM, &col_length, 0, OCI_ATTR_DATA_SIZE, errhp);
            
            switch (col_type) {
                case SQLT_INT:
                    OCIDefineByPos(stmthp, &defnp, errhp, i, (void *)&j, sizeof(j), SQLT_INT, 0, 0, 0, OCI_DEFAULT);
                    printf("%d\t", j);
                    break;
                case SQLT_CHR:
                    OCIDefineByPos(stmthp, &defnp, errhp, i, (void *)col_value, col_length, SQLT_STR, 0, 0, 0, OCI_DEFAULT);
                    printf("%s\t", col_value);
                    break;
                case SQLT_NUM:
                    OCIDefineByPos(stmthp, &defnp, errhp, i, (void *)&numhp, sizeof(numhp), SQLT_NUM, 0, 0, 0, OCI_DEFAULT);
                    OCINumberToString(envhp, numhp, (text *)"999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999", 99, (text *)col_value, MAX_COL_LENGTH, 0);
                    printf("%s\t", col_value);
                    break;
                case SQLT_DAT:
                    OCIDefineByPos(stmthp, &defnp, errhp, i, (void *)&datehp, sizeof(datehp), SQLT_DAT, 0, 0, 0, OCI_DEFAULT);
                    OCIDateTimeToText(envhp, errhp, datehp, (text *)"YYYY-MM-DD HH24:MI:SS", 19, (text *)col_value, MAX_COL_LENGTH);
                    printf("%s\t", col_value);
                    break;
                case SQLT_CLOB:
                    OCIDefineByPos(stmthp, &defnp, errhp, i, (void *)&lobhp, sizeof(lobhp), SQLT_CLOB, 0, 0, 0, OCI_DEFAULT);
                    OCILobRead(svchp, errhp, lobhp, &col_length, 1, (void *)col_value, col_length, 0, 0, 0, 0);
                    printf("%s\t", col_value);
                    break;
                default:
                    printf("Unknown data type\n");
                    break;
            }
        }
        printf("\n");
    }
    
    /* 提交事务 */
    if (status != OCI_NO_DATA) {
        printf("Error: %d\n", status);
    }
    OCITransCommit(svchp, errhp, OCI_DEFAULT);
    
    /* 断开连接，释放资源 */
    OCILogoff(svchp, errhp);
    OCIHandleFree(srvhp, OCI_HTYPE_SERVER);
    OCIHandleFree(svchp, OCI_HTYPE_SVCCTX);
    OCIHandleFree(stmthp, OCI_HTYPE_STMT);
    OCIHandleFree(transhp, OCI_HTYPE_TRANS);
    OCIHandleFree(envhp, OCI_HTYPE_ENV);
    
    return 0;
}

该示例包含了连接数据库、执行查询、输出结果以及提交事务的基本步骤。具体实现方式可能会因Oracle版本不同而有所差异，请根据实际情况进行调整。