Help Center/ Object Storage Service/ SDK Reference/ C/ Downloading an Object/ Downloading an Object
Updated on 2024-12-03 GMT+08:00
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Downloading an Object

If you have any questions during development, post them on the Issues page of GitHub.

You can use the get_object function to download an object.

Parameter Description

Field

Type

Mandatory or Optional

Description

option

The context of the bucket. For details, see Configuring option.

Mandatory

Bucket parameter

object_info

obs_object_info *

Mandatory

Object name and version number. For non-multi-version objects, set version to 0.

get_conditions

obs_get_conditions *

Mandatory

Sets filter conditions of the object and read range.

encryption_params

server_side_encryption_params *

Optional

Obtains the decryption settings of an object.

handler

obs_get_object_handler *

Mandatory

Callback function

callback_data

void *

Optional

Callback data

Sample Code

static void test_get_object()
{
    char *file_name = "./test";
    obs_object_info object_info;
    // Initialize option.
    obs_options option;
    init_obs_options(&option);
    option.bucket_options.host_name = "<your-endpoint>";
    option.bucket_options.bucket_name = "<Your bucketname>";

    // Hard-coded or plaintext AK/SK are risky. For security purposes, encrypt your AK/SK and store them in the configuration file or environment variables. In this example, the AK/SK are stored in environment variables for identity authentication. Before running this example, configure environment variables ACCESS_KEY_ID and SECRET_ACCESS_KEY.
    // Obtain an AK/SK pair on the management console. For details, see https://support.huaweicloud.com/intl/en-us/usermanual-ca/ca_01_0003.html.
    option.bucket_options.access_key = getenv("ACCESS_KEY_ID");
    option.bucket_options.secret_access_key = getenv("SECRET_ACCESS_KEY");

    // Set the object to be downloaded.
    memset(&object_info, 0, sizeof(obs_object_info));
    object_info.key = "<object key>";
    object_info.version_id = "<object version ID>";
    // Set the structure for storing downloaded object data based on service requirements.
    get_object_callback_data data;
    data.ret_status = OBS_STATUS_BUTT;
    data.outfile = write_to_file(file_name);
    // Define range download parameters.
    obs_get_conditions getcondition;
    memset(&getcondition, 0, sizeof(obs_get_conditions));
    init_get_properties(&getcondition);
    getcondition.start_byte = "<start byte>";
    // Download length. The default value is 0, indicating that the object end is read.
    getcondition.byte_count = "<byte count>";

    // Customize callback function for download.
    obs_get_object_handler get_object_handler =
    { 
        { &response_properties_callback,
          &get_object_complete_callback},
        &get_object_data_callback
    };

    get_object(&option, &object_info, &getcondition, 0, &get_object_handler, &data);
    if (OBS_STATUS_OK == data.ret_status) {
        printf("get object successfully. \n");
    }
    else
    {
        printf("get object faied(%s).\n", obs_get_status_name(data.ret_status));
    }
    fclose(data.outfile);
}
  • You can perform operations on the input streams of an object to read and write the object contents to a local file or to the memory.
  • getcondition can be left empty, indicating that the entire object is downloaded.
Parent topic: Downloading an Object