Example: Writing/reading of CSV file

General information on the supported CSV format

• Files in CSV format should have the extension .csv.
• The CRLF character (CR = Carriage Return, LF= Line Feed) is used to separate the individual data sets (rows) (Windows operating systems). I.e. each data set must be followed by a CRLF.
• The CSV file must end with a CRLF character.
• Binary data must be enclosed in single quotation marks. If no single quotation marks are used the data field may only contain numbers and/or letters.
• Data fields containing special characters/control characters are enclosed in double quotation marks. If the data field contains a double quotation mark a second double quotation mark is added.
• A special character is used for separating data fields (columns). The standard separator for the individual data fields used by the auxiliary functions is a semicolon. In Germany and Europe a semicolon used as a data field separator, in the USA a comma tends to be used. The separator can be configured from semicolon to comma via the global PLC variable DEFAULT_CSV_FIELD_SEP.
• Each data set should have the same number of data fields (columns).

Basic configuration of a CSV file with m columns and n rows (the CRLF characters are usually not visible and are indicated in the diagram with the letters CRLF)

"Field1Record1";"Field2Record1"; ... ;"Field(m)Record1"CRLF
"Field1Record2";"Field2Record2"; ... ;"Field(m)Record2"CRLF

...

"Field1Record(n)";"Field2Record(n)";    ... ;"Field(m)Record(n)"CRLF
 

Available function blocks and functions

• STRING_TO_CSVFIELD, ARG_TO_CSVFIELD: Converts PLC data into a data field in CSV format;
• CSVFIELD_TO_STRING, CSVFIELD_TO_ARG: Converts data field in CSV format to PLC data;
• FB_CSVMemBufferWriter: Generates data sets in a byte buffer from several data fields;
• FB_CSVMemBufferReader: Splits data sets in a byte buffer into individual data fields;

Write/read CSV file in text mode or binary mode

A CSV file can be read or written in text or binary mode with the aid of the PLC function blocks for file access. Depending on the selected mode there are differences with advantages and disadvantages.

In 99% of cases the CSV files can be read/written in text mode. Binary mode is only required in rare cases.

Example project

The project example actually contains 4 examples: 2 for write/read access in text mode (preferred) and 2 for write/read access in binary mode (rare):

P_TextModeRead();

P_TextModeWrite();

P_BinaryModeRead();

P_BinaryModeWrite();

Basic program sequence for reading a CSV file in text mode:

Step 1: Open the CSV file in text mode (FB_FileOpen). If successful go to step 2.

Step 2: Read a row with the function block FB_FileGets. Append a CR character (see notes in the table). If successful go to step 3 go, otherwise go to step 4 (the end of the file was reached or an error has occurred).

Step 3: Parse the read row with the function block FB_CSVMemBufferReader. The individual data fields are read. Then go to step 2 and read the next row. Repeat steps 2 and 3 until the end of the file is reached or an error occurs.

Step 4: Close the CSV file (FB_FileClose).

Basic program sequence for writing a CSV file in text mode.

Step 1: Open the CSV file in text mode (FB_FileOpen). If successful go to step 2.

Step 2: Use the function block FB_CSVMemBufferWriter to generate a new data set. The individual data fields are written into a buffer. This buffer may be a larger string. Remove the CR character at the end of the data set and go to step 3.

Step 3: Write a row with the function block FB_FilePuts. Repeat steps 2 and 3 until all data sets have been written. Then go to step 4.

Step 4: Close the file (FB_FileClose).

Requirements