我正在尝试使用C ++ Azure客户端库下载可能很大的Azure块blob。它不起作用,因为我不知道如何使用缓冲区大小初始化concurrency :: streams :: streambuf对象。我的代码看起来像这样:
// Assume blockBlob has been created correctly.
concurrency::streams::istream blobStream = blockBlob.open_read();
// I don't know how to initialize this streambuf:
concurrency::streams::streambuf<uint8_t> dlStreamBuf;
size_t nBytesReturned = 0, nBytesToRead = 65536;
do {
// This gets the exception "Invalid streambuf object":
concurrency::task<size_t> returnedTask = blobStream.read(dlStreamBuf, nBytesToRead);
nBytesReturned = returnedTask.get();
bytesSoFar += nBytesReturned;
// Process the data in dlStreamBuf here...
} while(nBytesReturned > 0);
blobStream.close();
请注意,上述streambuf不应与标准C ++ streambuf混淆。
谁能告诉我如何正确构建和初始化并发:: streams :: streambuf?
谢谢。
streambuf似乎是一个模板类。试试这个:
concurrency::streams::container_buffer<std::vector<uint8_t>> output_buffer;
size_t nBytesReturned = 0, nBytesToRead = 65536;
do {
// This gets the exception "Invalid streambuf object":
concurrency::task<size_t> returnedTask = stream.read(output_buffer, nBytesToRead);
nBytesReturned = returnedTask.get();
bytesSoFar += nBytesReturned;
// Process the data in dlStreamBuf here...
} while (nBytesReturned > 0);
stream.close();
我没有使用C ++的流方法,但是在C ++文档中提到了两种关于下载到文件或蒸汽的方法here
download_to_stream方法ex:
// Retrieve storage account from connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);
// Create the blob client.
azure::storage::cloud_blob_client blob_client = storage_account.create_cloud_blob_client();
// Retrieve a reference to a previously created container.
azure::storage::cloud_blob_container container = blob_client.get_container_reference(U("my-sample-container"));
// Retrieve reference to a blob named "my-blob-1".
azure::storage::cloud_block_blob blockBlob = container.get_block_blob_reference(U("my-blob-1"));
// Save blob contents to a file.
concurrency::streams::container_buffer<std::vector<uint8_t>> buffer;
concurrency::streams::ostream output_stream(buffer);
blockBlob.download_to_stream(output_stream);
std::ofstream outfile("DownloadBlobFile.txt", std::ofstream::binary);
std::vector<unsigned char>& data = buffer.collection();
outfile.write((char *)&data[0], buffer.size());
outfile.close();
替代方案,使用download_to_file:
// Retrieve storage account from connection string.
azure::storage::cloud_storage_account storage_account = azure::storage::cloud_storage_account::parse(storage_connection_string);
// Create the blob client.
azure::storage::cloud_blob_client blob_client = storage_account.create_cloud_blob_client();
// Retrieve a reference to a previously created container.
azure::storage::cloud_blob_container container = blob_client.get_container_reference(U("my-sample-container"));
// Retrieve reference to a blob named "my-blob-2".
azure::storage::cloud_block_blob text_blob = container.get_block_blob_reference(U("my-blob-2"));
// Download the contents of a blog as a text string.
utility::string_t text = text_blob.download_text();