Input and Output

Summary: The creation of this content was supported in some part by NSF grant 0538934.

Writing to File

Consider the function in Figure 1 where a set of numbers in a one-dimensional array represents the resulting noisy signal is to be written to a file. This section will outline the steps required to create files.

Figure 1: Noisy Signal Function

Create a new G program, right click in the G programming window and select File Dialog from the Functions >> Programming >> File I/O >> Advanced Functions menu. Drag and drop the File Dialog function onto the G programming window.

Figure 2: File Dialog

The Configure File Dialog dialog box automatically appears to configure the function. Accept the default configuration shown in Figure 3 to create a single file by clicking the OK button.

Figure 3: Configure File Dialog

The resulting diagram after closing the configuration dialog box is shown in . Optionally, right click on File Dialog and select View As Icon from the pop-up menu. This will save some real estate in the G programming window.

Figure 4: G File Dialog

Figure 5: View As Icon

From the Functions >> Programming >> File I/O menu select Open/Create File, Write Binary File and Close File functions.

Figure 6: File Input and Output Operators

Arrange the File I/O operations as shown in Figure 7.

Figure 7: Open, Write and Close File Diagram

Right click on the operation (0:open) terminal of the Open/Create File function (highlighted in Figure 8).

Figure 8: File Create Operation

Select Create >> Constant from the pop-up menu.

Figure 9: Create Operation Constant

Arrange the diagram to look as in Figure 10.

Figure 10: Operation Constant

Click on the down arrow in the operation constant just created and select open or create from the pop-up menu.

Figure 11: Open or Create File Operation

The resulting updated operation constant value is shown in Figure 12.

Figure 12: Create File to Write

Repeat the process to create a constant for the access (0:read/write) terminal (highlighted in Figure 13).

Figure 13: File Access Mode

Set the constant to write-only. Re-arrange the block diagram to look like the diagram shown in Figure 14. At this point, the file is set to create a new file for writing.

Figure 14: Write Only Mode

Get the Noisy Signal function and wire its output data to the Data terminal of the Write to Binary File function.

Figure 15: Writing Binary Data

Complete the diagram by connecting the Open, Write and Close file operations as shown in Figure 16.

Figure 16: Writing to File G Program

When this G program is executed, the standard file dialog box appears. Name the file to be written signal.dat.

Figure 17: Create File Dialog Box

Once the program completes executing, the signal.dat file is created and located in the location indicated by the path selected.

Figure 18: Data File signal.dat

Reading From Files

The signal.dat file created in the previous example will be used to read data from a file. As in the previous example, select the File Dialog, Open/Create File, Read from Binary File andClose File functions.

Figure 19: Operators to Read Files

Create constants by right clicking on the operation (0:open) and access (0:read/write) terminals of the Open/Create File operation. Set the constants to open and read-onlyrespectively (see Figure 20 ).

Figure 20: Set to Open and Read-Only

Similar to creating arrays, drop an array constant in the G diagram, drop a numeric constant onto the array constant and set the data type representation to double. Wire this array constant to the data type terminal of the Read from Binary File function as shown in Figure 21 .

Figure 21: Data Type to Read

In the Front Panel window, drop a Waveform Graph.

Figure 22: Graph for Data to be Read

With the data type specified, wire the data terminal of the Read from Binary File function to the Waveform Graph terminal as shown in Figure 23 .

Figure 23: Data to be Read

Complete the program by wiring refnum and error terminals of the Open/Create File, Read from Binary File and Close File functions as shown in Figure 24 .

Figure 24: Read Binary Data G Program

When this program is executed, a file dialog box appears. Select the signal.dat file and click OK.

Figure 25: Select Binary File to Read From

The binary data in signal.dat is read and plotted in a Waveform Graph. The result is shown in Figure 26

Figure 26: Read Data Graphed

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