Overview of the File System C APIs in libMapRClient

Although you can use the file system C APIs to perform other tasks, the most common use of the file system C APIs is to write to and read from files.

Review the following information for an overview of the steps required to use file system C APIs in libMapRClient:

1. Create a connection to the MapR file system running on a MapR cluster. For information about connections, see Establishing Connections to Filesystems.
2. Create or open a file. You can create explicitly or by calling one of the hdfsOpen() APIs and specifying a file that doesn’t exist. Opening a file sets the current offset to 0, the first byte in the file. You can move file offset explicitly with the hdfsSeek() API. Writes done by hdfsWrite() and reads done by hdfsRead() increment the offset by the number of bytes written or read.

   Use hdfsTell() to find out what the current offset is.

   For information about how to specify the location of a file to create or open, see Specifying Paths to Files and Directories.

3. Write to or read from the file. When you write to a file, you pass a buffer that contains the data that you want to write. Writes can be done from the default offset, which is 0 when the file is opened, appended to the end of the file, or done from an offset that you specify. Write buffers are flushed to the server periodically. For more information about writes, seeWriting to Files.

   When you read from a file, you pass a pointer to a buffer for storing the data that is read. Reads can be done from the default offset or from an offset that you specify. For more information about reads, see Reading from Files.

4. Close the file.

   Closing a file implicitly flushes any remaining write buffers to the server. It also frees resources that are associated with the file.

5. Disconnect from the file system.

For more detailed information about these steps, see: