Download a file (C++ SDK) - Object Storage Service - Alibaba Cloud Documentation Center

By default, the GetObject operation returns only the current version of an object from a versioning-enabled bucket.

Background information

When you call the GetObject operation to download an object in a bucket, you may obtain one of the following results:

If the current version of the object is a delete marker, OSS returns 404 Not Found.
If a version ID of the object is specified in the request, OSS returns the specified version of the object. If the version ID is set to null in the request, OSS returns the version whose version ID is null.
If the version ID specified in the request is the version ID of a delete marker, OSS returns 405 Method Not Allowed.

Usage notes

In this topic, the public endpoint of the China (Hangzhou) region is used. If you want to access OSS from other Alibaba Cloud services in the same region as OSS, use an internal endpoint. For more information about OSS regions and endpoints, see Regions and endpoints.
In this topic, an OSSClient instance is created by using an OSS endpoint. If you want to create an OSSClient by using custom domain names or Security Token Service (STS), see Create an OSSClient instance.

Permissions

By default, an Alibaba Cloud account has full permissions. RAM users or RAM roles under an Alibaba Cloud account do not have any permissions by default. The Alibaba Cloud account or account administrator must grant operation permissions through RAM Policy or Bucket policies.

API	Action	Definition
GetObject	`oss:GetObject`	Downloads an object.
	`oss:GetObjectVersion`	When downloading an object, if you specify the object version through versionId, this permission is required.
	`kms:Decrypt`	When downloading an object, if the object metadata contains X-Oss-Server-Side-Encryption: KMS, this permission is required.

Sample code

The following code shows how to download a file:

#include <alibabacloud/oss/OssClient.h>
using namespace AlibabaCloud::OSS;

int main(void)
{
    /* Initialize the OSS account information. */
            
    /* Set yourEndpoint to the Endpoint of the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set the Endpoint to https://oss-cn-hangzhou.aliyuncs.com. */
    std::string Endpoint = "yourEndpoint";
    /* Set yourRegion to the region where the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set the Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name, such as examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. The full path cannot contain the bucket name, such as exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";

    /* Initialize network resources. */
    InitializeSdk();

    ClientConfiguration conf;
    conf.signatureVersion = SignatureVersionType::V4;
    /* Obtain access credentials from environment variables. Before you run this sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are set. */
    auto credentialsProvider = std::make_shared<EnvironmentVariableCredentialsProvider>();
    OssClient client(Endpoint, credentialsProvider, conf);
    client.SetRegion(Region);

    /* Download the file to the local memory. */
    GetObjectRequest request(BucketName, ObjectName);
    request.setVersionId("yourObjectVersionId");
    auto outcome = client.GetObject(request);
    if (outcome.isSuccess()) {
        std::cout << "getObjectToBuffer" << " success, Content-Length:" << outcome.result().Metadata().ContentLength() << std::endl;
        /* Read the content of the downloaded object. */
        std::string content;
        *(outcome.result().Content()) >> content;
        std::cout << "getObjectToBuffer" << "content:" << content << std::endl;
        /* View the version ID of the downloaded object. */
        std::cout << "versionid:" << outcome.result().VersionId() << std::endl;
    }
    else {
            /* Handle the exception. */
            std::cout << "getObjectToBuffer fail" <<
        ",code:" << outcome.error().Code() <<
        ",message:" << outcome.error().Message() <<
        ",requestId:" << outcome.error().RequestId() << std::endl;
        return -1;
    }

    /* Release network resources. */
    ShutdownSdk();
    return 0;
}

References

For more information about the API operation used to download a file, see GetObject.