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    Object Storage Service:Multipart upload (C++ SDK)

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    Object Storage Service:Multipart upload (C++ SDK)

    Last Updated:Nov 29, 2025

    Object Storage Service (OSS) provides the multipart upload feature. Multipart upload allows you to split a large object into multiple parts to upload. After these parts are uploaded, you can call the CompleteMultipartUpload operation to combine the parts into a complete object.

    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.

    • To complete the entire multipart upload process, which includes the InitiateMultipartUpload, UploadPart, and CompleteMultipartUpload operations, you must have the oss:PutObject permission. For more information, see Grant custom permissions to a RAM user.

    Procedure

    To implement multipart upload, perform the following steps:

    1. Initiate a multipart upload.

      Call the InitiateMultipartUpload operation to obtain a globally unique upload ID from OSS.

    2. Upload parts.

      Call the UploadPart operation to upload data for each part.

      Note

      • In a multipart upload task, part numbers are used to identify the relative positions of the parts in an object. If you upload a part that has the same part number as an existing part, the existing part is overwritten by the uploaded part.

      • OSS includes the MD5 hash of each uploaded part in the ETag header in the response.

      • OSS calculates the MD5 hash of the uploaded parts and compares the MD5 hash with the MD5 hash that is calculated by OSS SDK for Java. If the two hashes are different, OSS returns the InvalidDigest error code.

    3. Complete the multipart upload.

      After all parts are uploaded, call the CompleteMultipartUpload operation to combine the parts into a complete object.

    Sample code for multipart upload

    The following sample code provides an example on how to implement a multipart upload task by following the multipart upload process:

    #include <alibabacloud/oss/OssClient.h>
#include <fstream>

int64_t getFileSize(const std::string& file)
{
    std::fstream f(file, std::ios::in | std::ios::binary);
    f.seekg(0, f.end);
    int64_t size = f.tellg();
    f.close();
    return size;
}

using namespace AlibabaCloud::OSS;

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. The full path cannot contain the bucket name. Example: 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 the sample code, make sure that the OSS_ACCESS_KEY_ID and OSS_ACCESS_KEY_SECRET environment variables are configured. */
    auto credentialsProvider = std::make_shared<EnvironmentVariableCredentialsProvider>();
    OssClient client(Endpoint, credentialsProvider, conf);
    client.SetRegion(Region);
  
    InitiateMultipartUploadRequest initUploadRequest(BucketName, ObjectName);
    /* (Optional) Set the storage class as shown in the following example. */
    //initUploadRequest.MetaData().addHeader("x-oss-storage-class", "Standard");

    /* Initiate the multipart upload event. */
    auto uploadIdResult = client.InitiateMultipartUpload(initUploadRequest);
    /* You can cancel the multipart upload event or list uploaded parts based on the upload ID. */
    /* To cancel a multipart upload event based on the upload ID, obtain the upload ID after you call InitiateMultipartUpload to initiate the event. */
    /* To list uploaded parts based on the upload ID, obtain the upload ID after you call InitiateMultipartUpload but before you call CompleteMultipartUpload. */ 
    auto uploadId = uploadIdResult.result().UploadId();
    std::string fileToUpload = "yourLocalFilename";
    /* The minimum part size is 100 KB and the maximum part size is 5 GB. The size of the last part can be less than 100 KB. */
    int64_t partSize = 100 * 1024;
    PartList partETagList;
    auto fileSize = getFileSize(fileToUpload);
    int partCount = static_cast<int>(fileSize / partSize);
    /* Calculate the number of parts. */
    if (fileSize % partSize != 0) {
        partCount++;
    }

    /* Upload each part. */
    for (int i = 1; i <= partCount; i++) {
        auto skipBytes = partSize * (i - 1);
        auto size = (partSize < fileSize - skipBytes) ? partSize : (fileSize - skipBytes);
        std::shared_ptr<std::iostream> content = std::make_shared<std::fstream>(fileToUpload, std::ios::in|std::ios::binary);
        content->seekg(skipBytes, std::ios::beg);

        UploadPartRequest uploadPartRequest(BucketName, ObjectName, content);
        uploadPartRequest.setContentLength(size);
        uploadPartRequest.setUploadId(uploadId);
        uploadPartRequest.setPartNumber(i);
        auto uploadPartOutcome = client.UploadPart(uploadPartRequest);
        if (uploadPartOutcome.isSuccess()) {
            Part part(i, uploadPartOutcome.result().ETag());
            partETagList.push_back(part);
        }
        else {
            std::cout << "uploadPart fail" <<
            ",code:" << uploadPartOutcome.error().Code() <<
            ",message:" << uploadPartOutcome.error().Message() <<
            ",requestId:" << uploadPartOutcome.error().RequestId() << std::endl;
        }

    }

    /* Complete the multipart upload. */
    /* When you complete the multipart upload, you must provide all valid partETags. After OSS receives the partETags, OSS verifies each part. After all parts are verified, OSS combines them into a complete object. */
    CompleteMultipartUploadRequest request(BucketName, ObjectName);
    request.setUploadId(uploadId);
    request.setPartList(partETagList);
    /* (Optional) Set the access control list (ACL) as shown in the following example. */
    //request.setAcl(CannedAccessControlList::Private);

    auto outcome = client.CompleteMultipartUpload(request);

    if (!outcome.isSuccess()) {
        /* Handle the exception. */
        std::cout << "CompleteMultipartUpload fail" <<
        ",code:" << outcome.error().Code() <<
        ",message:" << outcome.error().Message() <<
        ",requestId:" << outcome.error().RequestId() << std::endl;
        return -1;
    }

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

    When you call the CompleteMultipartUpload operation, you must provide the ETag value of each part. You can obtain the ETag value of each part in one of the following ways:

    • When you upload a part, the response includes the ETag value of the part. You can save and use this ETag value. This method is used in the preceding sample code.

    • Call the ListParts operation to query the ETag values of all uploaded parts.

    List uploaded parts

    Call the ListParts operation to list all successfully uploaded parts for a specific upload ID.

    Note

    By default, you can list a maximum of 1,000 uploaded parts at a time. If the number of uploaded parts exceeds 1,000, you must list them by page.

    List uploaded parts

    The following sample code shows how to list uploaded parts:

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

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. The full path cannot contain the bucket name. Example: exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";
    /* Specify the upload ID. The upload ID is obtained from the response to the InitiateMultipartUpload operation. You must obtain the upload ID before you call the CompleteMultipartUpload operation. */
    std::string UploadId = "yourUploadId";

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

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

    /* List uploaded parts. By default, a maximum of 1,000 parts are listed. */
    ListPartsRequest listuploadrequest(BucketName, ObjectName);
    listuploadrequest.setUploadId(UploadId);

    bool IsTruncated = false;

    do {
        auto listUploadResult = client.ListParts(listuploadrequest);
        if (!listUploadResult.isSuccess()) {
            /* Handle the exception. */
            std::cout << "ListParts fail" <<
            ",code:" << listUploadResult.error().Code() <<
            ",message:" << listUploadResult.error().Message() <<
            ",requestId:" << listUploadResult.error().RequestId() << std::endl;
            break;
        }
        else {
            for (const auto& part : listUploadResult.result().PartList()) {
                std::cout << "part"<<
                ",name:" << part.PartNumber() <<
                ",size:" << part.Size() <<
                ",etag:" << part.ETag() <<
                ",lastmodify time:" << part.LastModified() << std::endl;
            }
        }
        listuploadrequest.setPartNumberMarker(listUploadResult.result().NextPartNumberMarker());
        IsTruncated = listUploadResult.result().IsTruncated();
    } while (IsTruncated);

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

    List all uploaded parts by page

    The following sample code shows how to specify the number of parts to return on each page and list all parts by page:

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

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. The full path cannot contain the bucket name. Example: exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";
    /* Specify the upload ID. The upload ID is obtained from the response to the InitiateMultipartUpload operation. You must obtain the upload ID before you call the CompleteMultipartUpload operation. */
    std::string UploadId = "yourUploadId";

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

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

    /* List all uploaded parts by page. */
    /* Set the maximum number of parts to return on each page. */
    ListPartsRequest listuploadrequest(BucketName, ObjectName);
    listuploadrequest.setMaxParts(50);
    listuploadrequest.setUploadId(UploadId);
    bool IsTruncated = false;
    do {
        auto listuploadresult = client.ListParts(listuploadrequest);
        if (!listuploadresult.isSuccess()) {
            /* Handle the exception. */
            std::cout << "ListParts fail" <<
            ",code:" << listuploadresult.error().Code() <<
            ",message:" << listuploadresult.error().Message() <<
            ",requestId:" << listuploadresult.error().RequestId() << std::endl;
            break;
        }
        else {
            for (const auto& part : listuploadresult.result().PartList()) {
                std::cout << "part"<<
                ",name:" << part.PartNumber() <<
                ",size:" << part.Size() <<
                ",etag:" << part.ETag() <<
                ",lastmodify time:" << part.LastModified() << std::endl;
            }
        }  
        listuploadrequest.setPartNumberMarker(listuploadresult.result().NextPartNumberMarker());
        IsTruncated = listuploadresult.result().IsTruncated();
    } while (IsTruncated);

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

    List multipart upload events

    Call the ListMultipartUploads operation to list all ongoing multipart upload events. An ongoing multipart upload event is one that has been initiated but has not been completed or canceled.

    Note

    By default, you can list a maximum of 1,000 multipart upload events at a time. If the number of multipart upload events exceeds 1,000, you must list them by page.

    List multipart upload events

    The following sample code shows how to list multipart upload events.

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

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket";    

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

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

    /* List upload events. By default, a maximum of 1,000 events are listed. */
    ListMultipartUploadsRequest listmultiuploadrequest(BucketName);
	bool IsTruncated = false;
    do {
        auto listresult = client.ListMultipartUploads(listmultiuploadrequest);
        if (!listresult.isSuccess()) {
            /* Handle the exception. */
            std::cout << "ListMultipartUploads fail" <<
            ",code:" << listresult.error().Code() <<
            ",message:" << listresult.error().Message() <<
            ",requestId:" << listresult.error().RequestId() << std::endl;
            break;
        }
        else {
            for (const auto& part : listresult.result().MultipartUploadList()) {
                std::cout << "part"<<
                ",name:" << part.Key <<
                ",uploadid:" << part.UploadId <<
                ",initiated time:" << part.Initiated << std::endl;
            }
        }
        listmultiuploadrequest.setKeyMarker(listresult.result().NextKeyMarker()); 
        listmultiuploadrequest.setUploadIdMarker(listresult.result().NextUploadIdMarker());
        IsTruncated = listresult.result().IsTruncated();
    } while (IsTruncated);

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

    List all upload events by page

    The following sample code shows how to list all upload events by page:

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

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket"; 

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

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

    /* List all upload events by page. */
    /* Set the maximum number of upload events to return on each page. */
    ListMultipartUploadsRequest  listmultiuploadrequest(BucketName);
    listmultiuploadrequest.setMaxUploads(50);
    bool IsTruncated = false;
    do {
        auto listresult = client.ListMultipartUploads(listmultiuploadrequest);
        if (!listresult.isSuccess()) {
            /* Handle the exception. */
            std::cout << "ListMultipartUploads fail" <<
            ",code:" << listresult.error().Code() <<
            ",message:" << listresult.error().Message() <<
            ",requestId:" << listresult.error().RequestId() << std::endl;
            break;
        }
        else {
            for (const auto& part : listresult.result().MultipartUploadList()) {
                std::cout << "part"<<
                ",name:" << part.Key <<
                ",uploadid:" << part.UploadId <<
                ",initiated time:" << part.Initiated << std::endl;
            }
        }  
        listmultiuploadrequest.setKeyMarker(listresult.result().NextKeyMarker()); 
        listmultiuploadrequest.setUploadIdMarker(listresult.result().NextUploadIdMarker());
        IsTruncated = listresult.result().IsTruncated();
    } while (IsTruncated);

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

    Cancel a multipart upload event

    You can call the client.AbortMultipartUpload operation to cancel a multipart upload event. After a multipart upload event is canceled, you can no longer use the upload ID for any operations. The parts that have already been uploaded are also deleted.

    The following sample code shows how to cancel a multipart upload event: 

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

int main(void)
{
    /* Initialize the OSS account information. */
    
    /* Set Endpoint to the endpoint of the region in which 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 Region to the region in which the bucket is located. For example, if the bucket is in the China (Hangzhou) region, set Region to cn-hangzhou. */
    std::string Region = "yourRegion";
    /* Specify the bucket name. Example: examplebucket. */
    std::string BucketName = "examplebucket";
    /* Specify the full path of the object. The full path cannot contain the bucket name. Example: exampledir/exampleobject.txt. */
    std::string ObjectName = "exampledir/exampleobject.txt";
    /* Specify the upload ID. The upload ID is obtained from the response to the InitiateMultipartUpload operation. */
    std::string UploadId = "yourUploadId";

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

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

    /* Initiate the multipart upload event. */
    auto uploadIdResult = client.InitiateMultipartUpload(initUploadRequest);
    auto uploadId = uploadIdResult.result().UploadId();

    /* Cancel the multipart upload event. */
    AbortMultipartUploadRequest  abortUploadRequest(BucketName, ObjectName, uploadId);
    auto outcome = client.AbortMultipartUpload(abortUploadRequest);

    if (!outcome.isSuccess()) {
        /* Handle the exception. */
        std::cout << "AbortMultipartUpload 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 the complete sample code for multipart upload, see the GitHub example.

    • A multipart upload involves three API operations. For more information about the operations, see the following topics:

    • For more information about the API operation that you can call to cancel a multipart upload task, see AbortMultipartUpload.

    • For more information about the API operation that you can call to list uploaded parts, see ListUploadedParts.

    • For more information about the API operation that you can call to list all ongoing multipart upload tasks, see ListMultipartUploads. Ongoing multipart upload tasks include tasks that were initiated but are not completed or canceled.