CSE 154

Lecture 19: File I/O and Functions

PHP I/O Functions

Reading/Writing Files

Hello
how r u?

I'm fine

                

array("Hello\n", #0
"how r u?\n",    #1
"\n",            #2
"I'm fine\n"     #3
)
                

"Hello\n
how r u\n    # a single
\n           # string
I'm fine\n"
                

The file function returns lines of a file as an array (\n at end of each).

file_get_contents returns entire contents of a file as a single string.

file_put_contents writes a string into a file.

The file Function

          # display lines of file as a bulleted list
          $lines = file("todolist.txt");
          foreach ($lines as $line) { # for ($i = 0; $i < count($lines); $i++)
            print $line;
          }
          

PHP

file returns the lines of a file as an array of strings.

Each ends with \n; to strip it, use an optional second parameter:

          $lines = file("todolist.txt", FILE_IGNORE_NEW_LINES);
          

PHP

Common idiom: foreach or for loop over lines of file

Splitting/Joining Strings

          $array = explode(delimiter, string);
          $string = implode(delimiter, array);
          

PHP (template)

          $s = "CSE 154 A";
          $a = explode(" ", $s);     # ("CSE", "154", "A")
          $s2 = implode("...", $a);  # "CSE...154...A"
          

PHP (example)

explode and implode convert between strings and arrays.

For more complex strings, you can use regular expressions.

Example with explode

          Marty D Stepp
          Jessica K Miller
          Victoria R Kirst
          

contents of names.txt

          foreach (file("names.txt") as $name) {
            $tokens = explode(" ", $name);
            print "author: {$tokens[2]}, {$tokens[1]}\n";
          }
          

PHP

Unpacking an array: list

          list($var1, ..., $varN) = array;
          

PHP (template)

          Kyle Thayer
          (206) 154 2017
          17-154-0123
          

contents of personal.txt

          list($name, $phone, $ssn) = file("personal.txt");
          ...
          list($area_code, $prefix, $suffix) = explode(" ", $phone);
          

PHP

The list function "unpacks" an array into a set of variables.

When you now a file or line's exact length/format, use file and list to unpack it

Reading Directories

Can accept a general path with the * wildcard (more powerful).

glob Example

          # reverse all poems in the poetry directory
          $poems = glob("poetry/poem*.dat");
          foreach ($poems as $poemfile) {
            $text = file_get_contents($poemfile);
            file_put_contents($poemfile, strrev($text));
            print "I just reversed " . basename($poemfile) . "\n";
          }
          

PHP

glob can match a wildcard path with the * character

• glob("foo/bar/*.doc") returns all .doc files in the foo/bar subdirectory
• glob("food*") returns all files whose names begin with "food"

The basename function strips any leading directory from a file path

• basename("foo/bar/baz.txt") returns "baz.txt"

scandir Example

            foreach (scandir("taxes/old") as $filename) {
              print "I found a file: {$filename}\n";
            }
          

PHP

scandir includes current directory (".") and parent ("..") in the array.

Don't need basename with scandir; returns file names only without directory

Reading/Writing an Entire File

          # reverse a file
          $text = file_get_contents("poem.txt");
          $text = strrev($text);
          file_put_contents("poem.txt", $text);
          

PHP

file_get_contents returns entire contents of a file as a string

• if the file doesn't exist, you will get a warning and an empty return string

file_put_contents writes a string into a file, replacing its old contents

• if the file doesn't exist, it will be created

Appending to a File

          # add a new line to a file
          $new_text = "P.S. ILY, GTG TTYL!~";
          file_put_contents("poem.txt", $new_text, FILE_APPEND);
          

PHP

file_put_contents can be called with an optional third parameter to append (add to end) rather than overwrite.