Chapter 2 Storing and Retrieving Data

Question 1

Define and Show: fopen()

Answer 1

Opens a file.

$fp = fopen(“$DOCUMENT_ROOT/bobs/orders.txt, ‘ab’);

Question 2

fopen file mode: r

Answer 2

Read. Open the file for reading, beginning from the star of the file.

Question 3

fopen file mode: r+

Answer 3

Read. Open the file for reading and writing, beginning from the start of the file.

Question 4

fopen file mode: w

Answer 4

Write. Open the file for writing, beginning from the start of the file. If the file exists, delete the existing contents. If it does not exist, try to create it.

Question 5

fopen file mode: w+

Answer 5

Write. Open the file for writing and reading, beginning from the start of the file. If the file already exists, delete the existing contents. If it does not exist, try to create it.

Question 6

fopen file mode: x

Answer 6

Cautious write. Open the file for writing, beginning from the start of the file. If the file already exists, it will not be opened, fopen() will return false, and PHP will generate a warning.

Question 7

fopen file mode: x+

Answer 7

Cautious write. Open the file for writing and reading, beginning from the start of the file. If the file already exists, it will not be opened, fopen() will return false, and PHP will generate a warning.

Question 8

fopen file mode: a

Answer 8

Append. Open the file for appending (writing) only, starting from the end of the existing contents, if any. If it does not exist, try to create it.

Question 9

fopen file mode: a+

Answer 9

Append. Open the file for appending (writing) and reading, starting from the end of the existing contents, if any. If it does not exist, try to create it.

Question 10

fopen file mode: b

Answer 10

Binary. Used in conjunction with one of the other modes. You might want to use this mode if your file system differentiates between binary and text file. Windows systems differentiate; Unix systems do not. The PHP developers recommend you always us this option for maximum portability. It is the default mode.

Question 11

fopen file mode: t

Answer 11

Text. Used in conjunction with one of the other modes. This mode is an option only in Windows systems. It is not recommended except before you have ported your code to work with the b option.

Question 12

Define and Show: fwrite() or puts()

Answer 12

Write to a file.

fwrite($fp, $outputstring);

Question 13

Define and Show: @

Answer 13

Error suppression operator is used to suppress Wordpresses default error message.

@ $fp = fopen(“$DOCUMENT_ROOT/bobs/orders.txt, ‘ab’);

Question 14

Define and Show: file_put_contents()

Answer 14

This function writes the string to the file without any need for an fopen() function call.

Question 15

Define and Show: fclose()

Answer 15

Close a file.

fclose($fp);

Question 16

\n

Answer 16

New line.

Question 17

\t

Answer 17

Tab.

Question 18

Define and Show: feof()

Answer 18

File end of file. The feof() function takes a file handle as its single parameter. It returns true if the file pointer is at the end of the file.

while (!feof($fp)) {…

Question 19

Define and Show: fgets()

Answer 19

This function reads one line at a time from a file until it has read 998 bytes from the file.

$order = fgets($fp, 999);

Question 20

Define and Show: fgetss()

Answer 20

This function is similar to fgets() except that it strips out any PHP and HTML tags found in the string.

$order = fgets($fp, 999);

Question 21

Define and Show: fgetscsv()

Answer 21

This function breaks up lines when you have used a delimiting character, such as the tab character or a comma.

$order = fgetcsv($fp, 100, “\t”);

Question 22

Define and Show: readfile()

Answer 22

First option to read from a file. This function opens the file, echoes the content to the browser and then closes the file all in one go.

readfile(“$DOCUMENT_ROOT/bobs/orders.text”);

Question 23

Define and Show: fpassthru()

Answer 23

Second option to read from a file. First open a file using fopen(). Then pass the file pointer as an argument to fpassthru(), which dumps the contents of the file from the pointer’s position onward to the browser. It closes the file when it is finished.

$fp = fopen(“$DOCUMENT_ROOT/bobs/orders.txt”, ‘rb’);
fpassthru($fp);

Question 24

Define and Show: file()

Answer 24

Third option to read from a file. This function is identical to readfile() except that instead of echoing the file to the browser, it turns it into an array.

$filearray = file(“$DOCUMENT_ROOT/bobs/orders.txt”);

Question 25

Define and Show: file_get_contents()

Answer 25

Fourth option to read from a file. This function is identical to readfile() except that it returns the content of the file as a string instead of outputting it to the browser.

$mystring = file_get_contents(“$DOCUMENT_ROOT/bobs/orders.text”);

Question 26

Define and Show: fgetsc()

Answer 26

Reads a single character at a time from a file. It takes a file pointer as its only parameter and returns the next character in the file.

while(!feof($fp)) {
     $char = fgetc($fp);
     if (!feof($fp)) {
          echo $char == "\n" ? "<br />" : $char);
     }
}

Question 27

Define and Show: fread()

Answer 27

Reads an arbitrary number of bytes from a file. It reads up to length bytes, to the end of the file or network packet, whichever comes first.

$contents = fread($fp, 999);

Question 28

Define and Show: file_exists()

Answer 28

Checks to see if a file exists without actually opening it.

if (file_exists($DOCUMENT_ROOT/bobs/orders.txt)) {
echo ‘There are orders waiting to be processed.’;
} else {
echo ‘There are currently no orders’;
}

Question 29

Define and Show: filesize()

Answer 29

Checks the size of a file in bytes.

echo filesize(“$DOCUMENT_ROOT/bobs/orders.txt”);

Question 30

Define and Show: nl2br()

Answer 30

Converts the \n (new line) characters in the output to HTML line breaks (<br></br>).

echo nl2br(fread($fp, filesize($DOCUMENT_ROOT/bobs/orders.txt”)));

Question 31

Define and Show: unlink()

Answer 31

Used to delete the order file after the orders have been processed. There is no delete function.

unlink(“$DOCUMENT_ROOT/bobs/orders.txt”);

Question 32

Define and Show: rewind()

Answer 32

This function resets the file pointer to the beginning of the file.

rewind($fp);

Question 33

Define and Show: ftell()

Answer 33

This function reports how far into the file the pointer is in bytes.

echo ‘Final position of the file pointer is ‘.ftell($fp);

Question 34

Define and Show: fseek()

Answer 34

Sets the file pointer fp at the starting point from whence and moving offset bytes into the file. The optional whence parameter defaults to the value SEEK_SET, which is the start of the file. The other possible values are SEEK_CUR (the current location of the file pointer) and SEEK_END (the end of the file).

fseek($fp, 0); // start of the file.

Question 35

Define and Show: flock()

Answer 35

Locks a file. You need to pass it a pointer to an open file and a constant representing the kind of lock you require. It returns true if the lock was successfully acquired and false if it was not. You need to add it to all the scripts that use the file otherwise it is worthless.

$fp = fopen(“$DOCUMENT_ROOT/../orders/orders.txt”, ‘ab’); flock($fp, LOCK_EX); // lock the file for writing fwrite($fp, $outputstring);
flock($fp, LOCK_UN); // release write lock
fclose($fp);

Question 36

flock() parameters: LOCK_SH

Answer 36

Reading lock. The file can be shared with other readers.

Question 37

flock() parameters: LOCK_EX

Answer 37

Writing lock. This operation is exclusive; the file cannot be shared.

Question 38

flock() parameters: LOCK_UN

Answer 38

The existing lock is released.

Question 39

flock() parameters: LOCK_NB

Answer 39

Blocking is prevented while you are trying to acquire a lock.