在C++中實現Oracle數據庫連接池，可以使用Oracle官方提供的Oracle Call Interface (OCI) 庫

1. 首先，確保已經安裝了Oracle客戶端庫和OCI庫。可以從Oracle官網下載并安裝。

2. 包含必要的頭文件：

#include <occi.h>
#include<iostream>
#include<vector>
#include <mutex>
#include<condition_variable>

3. 定義一個連接池類，如下所示：

class OracleConnectionPool {
public:
    OracleConnectionPool(const std::string& connectionString, const std::string& userName, const std::string& password, int poolSize);
    ~OracleConnectionPool();

    oracle::occi::Connection* getConnection();
    void releaseConnection(oracle::occi::Connection* connection);

private:
    std::vector<oracle::occi::Connection*> connections_;
    std::vector<bool> connectionStatus_;
    std::mutex mutex_;
    std::condition_variable cv_;
};

4. 實現連接池類的構造函數、析構函數、獲取連接和釋放連接的方法：

OracleConnectionPool::OracleConnectionPool(const std::string& connectionString, const std::string& userName, const std::string& password, int poolSize) {
    for (int i = 0; i< poolSize; ++i) {
        oracle::occi::Environment* env = oracle::occi::Environment::createEnvironment(oracle::occi::Environment::DEFAULT);
        oracle::occi::Connection* conn = env->createConnection(userName, password, connectionString);
        connections_.push_back(conn);
        connectionStatus_.push_back(true);
    }
}

OracleConnectionPool::~OracleConnectionPool() {
    for (auto conn : connections_) {
        conn->close();
        oracle::occi::Environment::terminateEnvironment(conn->getEnvironment());
    }
}

oracle::occi::Connection* OracleConnectionPool::getConnection() {
    std::unique_lock<std::mutex> lock(mutex_);
    cv_.wait(lock, [this] { return std::any_of(connectionStatus_.begin(), connectionStatus_.end(), [](bool status) { return status; }); });

    auto it = std::find(connectionStatus_.begin(), connectionStatus_.end(), true);
    size_t index = std::distance(connectionStatus_.begin(), it);
    connectionStatus_[index] = false;

    return connections_[index];
}

void OracleConnectionPool::releaseConnection(oracle::occi::Connection* connection) {
    std::unique_lock<std::mutex> lock(mutex_);
    auto it = std::find(connections_.begin(), connections_.end(), connection);
    size_t index = std::distance(connections_.begin(), it);
    connectionStatus_[index] = true;
    cv_.notify_one();
}

5. 使用連接池：

int main() {
    OracleConnectionPool pool("localhost:1521/XE", "username", "password", 5);

    oracle::occi::Connection* conn = pool.getConnection();
    oracle::occi::Statement* stmt = conn->createStatement("SELECT * FROM your_table");
    oracle::occi::ResultSet* rs = stmt->executeQuery();

    while (rs->next()) {
        // 處理查詢結果
    }

    stmt->closeResultSet(rs);
    conn->terminateStatement(stmt);
    pool.releaseConnection(conn);

    return 0;
}

這樣就實現了一個簡單的Oracle數據庫連接池。請注意，這個實現僅作為示例，實際應用中可能需要根據需求進行調整和優化。