Reading text files

When reading data from text files, you often need to take particular actions at the end of each line or page. You certainly need to recognise when the end of data has been reached and it is time to stop reading.

Thus you need to look out for the special characters that represent end_of_line, end_of_page, and end_of_file.

TEXT_IO includes functions to check file position.

File position functions

END_OF_FILE

• next character is EOF ?
• next character is combination of EOL, EOP, EOF ?

END_OF_LINE

• next character is EOL ?
• next character is EOF ?

END_OF_PAGE

• next character is combination of EOL, EOP ?
• next character is EOF ?

Examples:

	if END_OF_PAGE (infile) then ...

	while not END_OF_FILE loop ...

Common file processing

Standard pieces of code can be written using these file position functions, to recognise the text file structure and process the data appropriately.

The appropriate code depends on how you view the data:

• you may want to read whole lines at a time, and don't care about reading characters individually
• you may need to read each character separately, and don't care about line or page boundaries
• you may need to watch out for line boundaries, and also need to process each character separately
• etc.

Here we show you how to write code to read and process:

• a file of lines
• a line of characters
• a file of lines of characters