Read from Text File (G Dataflow)

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Last Modified: January 12, 2018

Reads a specified number of bytes from a byte stream file.

Note

Strings are encoded in UTF-8. For strings containing characters in the U+0000 through U+007F range, the number of bytes in a string is equivalent to the number of characters. However, for strings containing the characters U+0080 through U+7FFFFFFF, the number of bytes is greater than the number of characters.

Programming Patterns

Opening, Processing, and Closing Files

prompt

Custom message in the title bar of the file dialog box that appears when you do not wire a value to the input path.

file path

The file that this node reads.

This input can be a reference to a file or an absolute file path. The node opens the specified file without requiring you to call Open/Create/Replace File first.

If you wire a path to file, this node opens the file before reading from it and closes it afterwards.

If you specify an empty path, a relative path, or a path to a non-existent file, this node returns an error.

count

The maximum number of data elements to read. Data elements are instances of the specified data type.

If this node reaches the end of the file before reading the specified number of data elements, the node returns the available data elements along with an end-of-file error.

If count is -1, the node reads the entire file, characters or lines, unless the size of the file is too large to be represented by a 32-bit integer. In this case, the node returns an error. If count is less than -1, the node returns an error.

Note

If you wire a file size with a data type other than a 32-bit integer to count, this node coerces the data type to a 32-bit integer. This means the program may not read the amount of data you intend. If you wire -1 to count and the size of the file you want to read is too large to be represented by a 32-bit integer, the program returns an error.

Default: 1

error in

Error conditions that occur before this node runs.

The node responds to this input according to standard error behavior.

Standard Error Behavior

Many nodes provide an error in input and an error out output so that the node can respond to and communicate errors that occur while code is running. The value of error in specifies whether an error occurred before the node runs. Most nodes respond to values of error in in a standard, predictable way.

error in does not contain an error	error in contains an error

If no error occurred before the node runs, the node begins execution normally. If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.	If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Default: No error

refnum out

A reference to the file that this node uses.

text

The string read from the file.

cancelled?

A Boolean value that indicates whether the user cancelled the dialog box that appears if no input file was wired to this node.

True	The dialog box was cancelled.
False	The dialog box was not cancelled, or the dialog box did not appear.

error out

Error information.

The node produces this output according to standard error behavior.

Standard Error Behavior

error in does not contain an error	error in contains an error

If no error occurred before the node runs, the node begins execution normally. If no error occurs while the node runs, it returns no error. If an error does occur while the node runs, it returns that error information as error out.	If an error occurred before the node runs, the node does not execute. Instead, it returns the error in value as error out.

Configuring Read from Text File to Read Characters or Lines

By default, this node reads all characters from the text file. Wire an integer value to count to specify how many individual characters you want to read starting with the first character. Right-click the node and place a checkmark next to the Read Lines option in the shortcut menu to read individual lines from the text file. When you select the Read Lines option in the shortcut menu, wire an integer value tocount to specify how many individual lines you want to read from the file starting with the first line.

Read and Write Permissions for Read from Text File

This node opens files as read-only. This node returns a permissions error if you wire the refnum outoutput of this node to the file input of a write node. Use the Open/Create/Replace File node to open the file with the default read/write access and wire the refnum to the read and write nodes. Use the Set File Position node if you need to perform random access.

Preventing Read from Text File from Converting End-of-Line Characters to Line Feed Characters

This node converts all platform-dependent end-of-line characters to line feed characters unless you right-click the node and remove the checkmark next to the Convert EOL shortcut menu item.

Where This Node Can Run:

Desktop OS: Windows

FPGA: All devices (only within an optimized FPGA VI)

Web Server: Not supported in VIs that run in a web application

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