Advanced Commercial Web Site Design: ServerSide Scripting

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Advanced Commercial Web Site Design Server-Side
Scripting

• Session 7 String and File functions

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Outline

• Manipulating Strings
• Getting specific characters
• String functions
• String length and locating specific characters
• Substrings
• Parsing strings
• Tokenizer
• File handling
• Open a file
• Read / Write a file

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Strings

• A sequence of characters that are grouped
  together as a unit and
• can be passed as arguments in methods
• can be assigned to variables
• can be outputted to the web-page
• A string consists of the characters and is
  included in either
• Single quotes ( ) or hello
• Double quotes ( ) hello
• Certain characters cannot by used as they are,
  thus we need to escape them.

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Characters in Strings

• A string can be treated as an array of
  characters. The index of the first character is
  0, the second characters index is 1, etc.
• Example

• lastName Doe // string
• // to obtain the first character get the first
  element of the array
• char1 lastName0 D
• char1 lastName1 o
• char3 lastName2 e
• echo( char3.char1.char2)
• eDo

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Length of a String

• Method strlen(string). The length of the
  specified string is the number of characters this
  string consists of.
• Example

s1 Hello s2 // to obtain the length
of this string len1 strlen(s1) 5 len2
strlen(s2) 0 echo( Length of s1 len1,
Length of s2 len2) Length of Hello 5,
Length of 0
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Locate a specific char in a String

• Method strpos(string, char). Returns the index
  (numeric position) of the specified character of
  its first occurrence in the specified string.
• Example
• If the specified character in the specified
  string is not found, the function will return
  FALSE.

• s1 Hello
• // to locate a specific character on this string
• pos1 strpos(s1, e) Hello e
• pos2 strpos(s1, o) Hello o
• echo( Index of e in s1 pos1, Index of o in
  s1 pos2)
• Index of e in Hello 1, Index of o in Hello
  4

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Substrings of a String

• Method substr(string, startIndex ,length).
  Returns the portion of the specified string, that
  starts at startIndex until the end. If length is
  specified, it will read length characters
  starting from startIndex.
• Example
• If start is negative, the returned string will
  start at the start'th character from the end of
  string.

s1 Hello world! // to obtain a portion of
the original string sub1 substr(s1,
6) sub2 substr(s1, 6, 5) echo(
Substring of s1 starting at 7th character
sub1) Substring of Hello world! starting at
6th character world! echo( Substring of s1
starting at 7th character for 5 chars sub2)
Substring of Hello world! starting at 6th
character for 5 chars world
sub3 substr(s1, -3) ld!
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Parsing strings

• The process of breaking up a string into
  substrings is called tokenizing. Special
  delimiters exist between the substrings, and
  method (tokenizer) for tokenizing can pick up
  automatically the delimiters and substrings,
  providing for efficient parsing of the long
  string.
• Method strtok(str, delimiter)splits a string
  (str) into smaller strings (tokens), with each
  token being delimited by any character from
  token. i.e. strtok breaks a string using single
  _characters_ , the best part is you can use
  multiple characters at the same time.

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A simple tokenizer

• Example
• s1 It is a nice_day!
• // to obtain tokens, separated by the (space or
  underscore) delimiter
• token strtok(s1, _)
• echo token . ltbrgt
• echo strtok( _) .ltbrgt
• echo strtok( _) .ltbrgt
• echo strtok( _) .ltbrgt
• echo strtok( _) .ltbrgt

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Another tokenizer

• Example
• s1 LastName._.FirstName._.CardNumber
• // to obtain tokens, separated by the
  (underscore) delimiter
• tokens explode (_, s1)
• for(i 0 i lt count(tokens) i)
• echo tokens i .ltbrgt

Method explode ( string separator, string string
, int limit ) Returns an array of strings,
each of which is a substring of string formed by
splitting it on boundaries formed by the string
separator. If limit is set, the returned array
will contain a maximum of limit elements with the
last element containing the rest of string.
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Exercise 7.1 Tokenizer

• Create a long string with a distinctive delimiter
  in between the portions of the string you are
  interested in.e.g. Name Surname Age Height
• Tokenize the string and output each of the tokens
  on a separate line in the resulting web-page.
  Also output the original string and the delimiter
  used to parse it.
• Test for correct results for different delimiters!

http//uk2.php.net/strings for detailed
description of String functions
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File handling

• Two main operations are defined for (any type of)
  files
• Read from a file Read the data stored in a file
  and put them in the memory
• Write to a file Put the data of the memory into
  a file, for later use (persistency)
• and an optional combined operation
• Append to a file Write data at the end of an
  existing file (do not overwrite the original file)

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File handling (cont.)

• The process of accessing a file for either
  reading or writing includes
• Open the file, in a specific mode (see below)
• Depending on the mode, perform some operations to
  that file
• Close the file
• Think about working on MS Word.
• Modes of operation

• r Read-only
• w Write-only
• Create a new file if not exist overwrite if
  exists
• a Write-only
• Write to the end of file

• r Read and Write
• w Write and Read
• Create a new file if not exist overwrite if
  exists
• a Read and Write
• Read and Write to the end of file

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Opening a File

• Method fd fopen( fileName, mode)
• (fd is a file handler which can be used later
  to represent the opened file.)

HTTP fopen fd fopen(http//www.google.com/,
r) FTP fopen fd fopen(ftp//userpass_at_ftp.
till.me.uk/file.txt, r) // only r and w
is supported Filesystem fopen fd
fopen(/var/www/html/cw3/user_X/session7/test.inc
, r)
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Opening a File (cont.)

• Error Handling What if something goes wrong?
• If the URL is not correct
• If the file does not exist
• If we do not have permissions
• etc.
• Example

fd fopen(/var/www/html/cw3/user_X/session7/tes
t.inc, r) or die(Error opening the file!)
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Reading a File

• Reads the contents of the opened file
  (filePointer/handler) and assigns them as a
  string to a variable.
• Method freadString fread( filePointer, length
  )
• Example

// open the file filename /var/www/html/cw3/us
er_X/session7/test.inc fd fopen( filename,
r) fstring fread( fd, filesize(filename)
) // close the file fclose(fd)
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Writing to a File

• Writes the value of a variable to the open file
  (filePointer).
• Method fwrite( filePointer, varName )
• Example

filename test.inc // open the file fd
fopen( filename, w) stringToWrite Hello
world fwrite( fd, stringToWrite) // close
the file fclose(fd)
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Closing a File

• Closes the open file (filePointer). Its
  advisable to always close the files that open
  during the execution of the script. There is a
  limited amount of pointers and you may run out!
• Method fclose( filePointer )

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Exercise 7.2 Create a file

• Write a number of strings in a file called
  test.txt and upload it to the same directory as
  where your PHP file is located.
• Read the strings stored in that file and present
  them in the resulting web-page, one per line.
• HINT You may add the delimiter \r\n which
  represents New Line at the end of each string
  when writing them to the file. When reading,
  parse them according to this delimiter!

http//uk2.php.net/manual/en/ref.filesystem.php
for details of File functions in PHP