Reading and writing files

For a file small enough to hold in memory, one call reads or writes all of it.

#import "std/fs"
#import "std/containers"

print "Whole files"
dim as ustring dir_ = fs.CreateTempDir( "tbe" ).Value( )
dim as ustring p = fs.PathJoin( dir_, "todo.txt" )

fs.WriteAllText( p, "buy milk" & chr( 10 ) )
fs.AppendAllText( p, "call home" & chr( 10 ) )

dim lines as containers.Array( of ustring )
print fs.ReadAllLines( p, lines ).Value( ); " lines"
for each ln in lines
    print "- "; ln
next

'' Bytes, not text: exactly what is on disk.
dim bytes as containers.Array( of ubyte )
fs.ReadAllBytes( p, bytes )
print bytes.Count( ); " bytes"

'' Replace a file so that a reader sees the old one or the new one.
fs.WriteAtomic( p, "all done" & chr( 10 ) )
print fs.ReadAllText( p ).Value( );

fs.RemoveDirAll( dir_ )

Output

Whole files
 2 lines
- buy milk
- call home
 19 bytes
all done

ReadAllLines removes each line's ending, whether it is a line feed or a carriage return and line feed, and a final line feed does not make an empty last line. Text is read as UTF-8 unless the file starts with a byte-order mark that says otherwise.

WriteAtomic writes a temporary file beside p and then puts it in p's place. A program reading at the same moment sees the old contents or the new, and a crash part-way through leaves the old file as it was. Use it to save a configuration or a document.

Activities

1. Read a file that is not there with ReadAllLines and print the failure's Message( ).
2. Write the text with a carriage return and line feed after each line and check that ReadAllLines gives the same two lines.