Quickstart: Azure Blob Storage client library for C++

Article
11/24/2023

Get started with the Azure Blob Storage client library for C++. Azure Blob Storage is Microsoft's object storage solution for the cloud. Follow these steps to install the package and try out example code for basic tasks.

| API reference documentation | Library source code | Samples |

Prerequisites

Azure subscription - create one for trial
Azure storage account - create a storage account
C++ compiler
CMake
vcpkg - C and C++ package manager

Setting up

This section walks you through preparing a project to work with the Azure Blob Storage client library for C++. The easiest way to acquire the Azure SDK for C++ is to use the vcpkg package manager.

Install the packages

Use the vcpkg install command to install the Azure Blob Storage library for C++ and necessary dependencies:

vcpkg.exe install azure-storage-blobs-cpp

The Azure Identity library is needed for passwordless connections to Azure services:

vcpkg.exe install azure-identity-cpp

For more information on project setup and working with the Azure SDK for C++, see the Azure SDK for C++ readme.

Create the project

In Visual Studio, create a new C++ console application for Windows called BlobQuickstart.

Visual Studio dialog for configuring a new C++ Windows console app

Object model

Azure Blob Storage is optimized for storing massive amounts of unstructured data. Unstructured data is data that doesn't adhere to a particular data model or definition, such as text or binary data. Blob Storage offers three types of resources:

The storage account
A container in the storage account
A blob in the container

The following diagram shows the relationship between these resources.

Diagram of Blob Storage architecture

Use these C++ classes to interact with these resources:

BlobServiceClient: The BlobServiceClient class allows you to manipulate Azure Storage resources and blob containers.
BlobContainerClient: The BlobContainerClient class allows you to manipulate Azure Storage containers and their blobs.
BlobClient: The BlobClient class allows you to manipulate Azure Storage blobs. It's the base class for all specialized blob classes.
BlockBlobClient: The BlockBlobClient class allows you to manipulate Azure Storage block blobs.

Code examples

These example code snippets show you how to do the following tasks with the Azure Blob Storage client library for C++:

Add include files
Authenticate to Azure and authorize access to blob data
Create a container
Upload blobs to a container
List the blobs in a container
Download blobs
Delete a container

Add include files

From the project directory:

Open the BlobQuickstart.sln solution file in Visual Studio
Inside Visual Studio, open the BlobQuickstart.cpp source file
Remove any code inside main that was autogenerated
Add #include and using namespace statements

#include <iostream>
#include <azure/core.hpp>
#include <azure/identity/default_azure_credential.hpp>
#include <azure/storage/blobs.hpp>

using namespace Azure::Identity;
using namespace Azure::Storage::Blobs;

Authenticate to Azure and authorize access to blob data

Application requests to Azure Blob Storage must be authorized. Using the DefaultAzureCredential class provided by the Azure Identity client library is the recommended approach for implementing passwordless connections to Azure services in your code, including Blob Storage.

You can also authorize requests to Azure Blob Storage by using the account access key. However, this approach should be used with caution. Developers must be diligent to never expose the access key in an unsecure location. Anyone who has the access key is able to authorize requests against the storage account, and effectively has access to all the data. DefaultAzureCredential offers improved management and security benefits over the account key to allow passwordless authentication. Both options are demonstrated in the following example.

Passwordless (Recommended)
Connection String

The Azure Identity library provides Microsoft Entra token authentication support across the Azure SDK. It provides a set of TokenCredential implementations which can be used to construct Azure SDK clients which support Microsoft Entra token authentication. DefaultAzureCredential supports multiple authentication methods and determines which method should be used at runtime.

Assign roles to your Microsoft Entra user account

When developing locally, make sure that the user account that is accessing blob data has the correct permissions. You'll need Storage Blob Data Contributor to read and write blob data. To assign yourself this role, you'll need to be assigned the User Access Administrator role, or another role that includes the Microsoft.Authorization/roleAssignments/write action. You can assign Azure RBAC roles to a user using the Azure portal, Azure CLI, or Azure PowerShell. You can learn more about the available scopes for role assignments on the scope overview page.

In this scenario, you'll assign permissions to your user account, scoped to the storage account, to follow the Principle of Least Privilege. This practice gives users only the minimum permissions needed and creates more secure production environments.

The following example will assign the Storage Blob Data Contributor role to your user account, which provides both read and write access to blob data in your storage account.

Important

In most cases it will take a minute or two for the role assignment to propagate in Azure, but in rare cases it may take up to eight minutes. If you receive authentication errors when you first run your code, wait a few moments and try again.

In the Azure portal, locate your storage account using the main search bar or left navigation.
On the storage account overview page, select Access control (IAM) from the left-hand menu.
On the Access control (IAM) page, select the Role assignments tab.
Select + Add from the top menu and then Add role assignment from the resulting drop-down menu.
Use the search box to filter the results to the desired role. For this example, search for Storage Blob Data Contributor and select the matching result and then choose Next.
Under Assign access to, select User, group, or service principal, and then choose + Select members.
In the dialog, search for your Microsoft Entra username (usually your user@domain email address) and then choose Select at the bottom of the dialog.
Select Review + assign to go to the final page, and then Review + assign again to complete the process.

To assign a role at the resource level using the Azure CLI, you first must retrieve the resource id using the az storage account show command. You can filter the output properties using the --query parameter.

az storage account show --resource-group '<your-resource-group-name>' --name '<your-storage-account-name>' --query id

Copy the output Id from the preceding command. You can then assign roles using the az role command of the Azure CLI.

az role assignment create --assignee "<user@domain>" \
    --role "Storage Blob Data Contributor" \
    --scope "<your-resource-id>"

To assign a role at the resource level using Azure PowerShell, you first must retrieve the resource ID using the Get-AzResource command.

Get-AzResource -ResourceGroupName "<yourResourceGroupname>" -Name "<yourStorageAccountName>"

Copy the Id value from the preceding command output. You can then assign roles using the New-AzRoleAssignment command in PowerShell.

New-AzRoleAssignment -SignInName <user@domain> `
    -RoleDefinitionName "Storage Blob Data Contributor" `
    -Scope <yourStorageAccountId>

You can authorize access to data in your storage account using the following steps:

Make sure you're authenticated with the same Microsoft Entra account you assigned the role to on your storage account. You can authenticate via Azure CLI. Sign in to Azure through the Azure CLI using the following command:
```
az login
```
To use DefaultAzureCredential, make sure that the azure-identity-cpp package is installed and the following #include is added:
```
#include <azure/identity/default_azure_credential.hpp>
```

Add this code to the end of main(). When the code runs on your local workstation, DefaultAzureCredential uses the developer credentials for Azure CLI to authenticate to Azure.

// Initialize an instance of DefaultAzureCredential
 auto defaultAzureCredential = std::make_shared<DefaultAzureCredential>();

 auto accountURL = "https://<storage-account-name>.blob.core.chinacloudapi.cn";
 BlobServiceClient blobServiceClient(accountURL, defaultAzureCredential);

Make sure to update the storage account name in the URI of your BlobServiceClient object. The storage account name can be found on the overview page of the Azure portal.

Note

When using the C++ SDK in a production environment, it's recommended that you only enable credentials that you know your application will use. Instead of using DefaultAzureCredential, you should authorize using a specific credential type, or by using ChainedTokenCredential with the supported credentials.

A connection string includes the storage account access key and uses it to authorize requests. Always be careful to never expose the keys in an unsecure location.

Note

To authorize data access with the storage account access key, you'll need permissions for the following Azure RBAC action: Microsoft.Storage/storageAccounts/listkeys/action. The least privileged built-in role with permissions for this action is Reader and Data Access, but any role which includes this action will work.

Sign in to the Azure portal.
Locate your storage account.
In the storage account menu pane, under Security + networking, select Access keys. Here, you can view the account access keys and the complete connection string for each key.
In the Access keys pane, select Show keys.
In the key1 section, locate the Connection string value. Select the Copy to clipboard icon to copy the connection string. You'll add the connection string value to an environment variable in the next section.

You can see the connection string for your storage account using the az storage account show-connection-string command.

az storage account show-connection-string --name "<your-storage-account-name>"

You can assemble a connection string with PowerShell using the Get-AzStorageAccount and Get-AzStorageAccountKey commands.

$saName = "yourStorageAccountName"
$rgName = "yourResourceGroupName"
$sa = Get-AzStorageAccount -StorageAccountName $saName -ResourceGroupName $rgName

$saKey = (Get-AzStorageAccountKey -ResourceGroupName $rgName -Name $saName)[0].Value

'DefaultEndpointsProtocol=https;AccountName=' + $saName + ';AccountKey=' + $saKey + ';EndpointSuffix=core.chinacloudapi.cn'

Configure your storage connection string

After you copy the connection string, write it to a new environment variable on the local machine running the application. To set the environment variable, open a console window, and follow the instructions for your operating system. Replace <yourconnectionstring> with your actual connection string.

Windows:

setx AZURE_STORAGE_CONNECTION_STRING "<yourconnectionstring>"

After you add the environment variable in Windows, you must start a new instance of the command window.

Linux:

export AZURE_STORAGE_CONNECTION_STRING="<yourconnectionstring>"

The following code example retrieves the connection string for the storage account from the environment variable created earlier, and uses the connection string to construct a service client object.

Add this code to the end of main():

    // Retrieve the connection string for use with the application. The storage
    // connection string is stored in an environment variable on the machine
    // running the application called AZURE_STORAGE_CONNECTION_STRING.
    // Note that _MSC_VER is set when using MSVC compiler.
    static const char* AZURE_STORAGE_CONNECTION_STRING = "AZURE_STORAGE_CONNECTION_STRING";

#if !defined(_MSC_VER)
    const char* connectionString = std::getenv(AZURE_STORAGE_CONNECTION_STRING);
#else
	// Use getenv_s for MSVC
	size_t requiredSize;
	getenv_s(&requiredSize, NULL, NULL, AZURE_STORAGE_CONNECTION_STRING);
	if (requiredSize == 0) {
		throw std::runtime_error("missing connection string from env.");
	}
	std::vector<char> value(requiredSize);
	getenv_s(&requiredSize, value.data(), value.size(), AZURE_STORAGE_CONNECTION_STRING);
	std::string connectionStringStr = std::string(value.begin(), value.end());
	const char* connectionString = connectionStringStr.c_str();
#endif

	auto blobServiceClient = BlobServiceClient::CreateFromConnectionString(connectionString);

Important

The account access key should be used with caution. If your account access key is lost or accidentally placed in an insecure location, your service may become vulnerable. Anyone who has the access key is able to authorize requests against the storage account, and effectively has access to all the data. DefaultAzureCredential provides enhanced security features and benefits and is the recommended approach for managing authorization to Azure services.

Create a container

Decide on a name for the new container. Then create an instance of BlobContainerClient and create the container.

Important

Container names must be lowercase. For more information about naming containers and blobs, see Naming and Referencing Containers, Blobs, and Metadata.

Add this code to the end of main():

std::string containerName = "myblobcontainer";
auto containerClient = blobServiceClient.GetBlobContainerClient("myblobcontainer");

// Create the container if it does not exist
std::cout << "Creating container: " << containerName << std::endl;
containerClient.CreateIfNotExists();

Upload blobs to a container

The following code snippet:

Declares a string containing "Hello Azure!"
Gets a reference to a BlockBlobClient object by calling GetBlockBlobClient on the container from the Create a container section.
Uploads the string to the blob by calling the UploadFrom function. This function creates the blob if it doesn't already exist, or updates it if it does.

Add this code to the end of main():

std::string blobName = "blob.txt";
uint8_t blobContent[] = "Hello Azure!";
// Create the block blob client
BlockBlobClient blobClient = containerClient.GetBlockBlobClient(blobName);

// Upload the blob
std::cout << "Uploading blob: " << blobName << std::endl;
blobClient.UploadFrom(blobContent, sizeof(blobContent));

List the blobs in a container

List the blobs in the container by calling the ListBlobs function. Only one blob has been added to the container, so the operation returns just that blob.

Add this code to the end of main():

std::cout << "Listing blobs..." << std::endl;
auto listBlobsResponse = containerClient.ListBlobs();
for (auto blobItem : listBlobsResponse.Blobs)
{
    std::cout << "Blob name: " << blobItem.Name << std::endl;
}

Download blobs

Get the properties of the uploaded blob. Then, declare and resize a new std::vector<uint8_t> object by using the properties of the uploaded blob. Download the previously created blob into the new std::vector<uint8_t> object by calling the DownloadTo function in the BlobClient base class. Finally, display the downloaded blob data.

Add this code to the end of main():

auto properties = blobClient.GetProperties().Value;
std::vector<uint8_t> downloadedBlob(properties.BlobSize);

blobClient.DownloadTo(downloadedBlob.data(), downloadedBlob.size());
std::cout << "Downloaded blob contents: " << std::string(downloadedBlob.begin(), downloadedBlob.end()) << std::endl;

Delete a Blob

The following code deletes the blob from the Azure Blob Storage container by calling the BlobClient.Delete function.

std::cout << "Deleting blob: " << blobName << std::endl;
blobClient.Delete();

Delete a container

The following code cleans up the resources the app created by deleting the entire container by using BlobContainerClient.Delete.

Add this code to the end of main():

std::cout << "Deleting container: " << containerName << std::endl;
containerClient.Delete();

Run the code

This app creates a container and uploads a text file to Azure Blob Storage. The example then lists the blobs in the container, downloads the file, and displays the file contents. Finally, the app deletes the blob and the container.

The output of the app is similar to the following example:

Azure Blob Storage - C++ quickstart sample
Creating container: myblobcontainer
Uploading blob: blob.txt
Listing blobs...
Blob name: blob.txt
Downloaded blob contents: Hello Azure!
Deleting blob: blob.txt
Deleting container: myblobcontainer

Next steps

In this quickstart, you learned how to upload, download, and list blobs using C++. You also learned how to create and delete an Azure Blob Storage container.

To see a C++ Blob Storage sample, continue to:

Azure Blob Storage client library for C++ samples

Quickstart: Azure Blob Storage client library for C++

Prerequisites

Setting up

Install the packages

Create the project

Object model

Code examples

Add include files

Authenticate to Azure and authorize access to blob data

Assign roles to your Microsoft Entra user account

Sign in and connect your app code to Azure using DefaultAzureCredential

Create a container

Upload blobs to a container

List the blobs in a container

Download blobs

Delete a Blob

Delete a container

Run the code

Next steps

Additional resources