PHP and MySQL by Example- P10

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Nội dung Text: PHP and MySQL by Example- P10

The ftell() Function—Finding the Current Position in a File If you have read some data from a file and want to keep track of where you were in the file when you stopped reading, the ftell() function will return the current byte position, the number of bytes from the beginning of the file, and where the next read operation will start. This can be used in conjunction with the seek() function to return to the correct position in the file. (If you are using text mode, the carriage return and linefeed translation will be part of the byte count.) Format int ftell ( resource handle ) Example: $filehandle("myfile", "r"); $contents=fgets($filehandle, 1024); echo ftell( $filehandle); // Current read postion in bytes, // starting at byte 1024 Example 11.9. Code View: The ftell() Function Marking a Position in a File Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Explanation 1 A file is opened for reading. 2 The variable, $substring, is assigned the string "eastern", a string that will be searched for in the file that was just opened. 3 As each line is read from the file, the substr_count() function will search for the string "eastern" in a line and return the number of times it was found. The first time this function returns 1 or more, the next line will be entered. 4 The ftell() function will return the byte position of where the next read operation will take place. The line containing "eastern" has already been read. The byte position is the number of characters from the beginning of the file. This value is saved in $bytes, to be used later with the fseek() function. 5 The fseek() function will start at the beginning of the file, byte 0, and move to the position returned from ftell(), byte 291, in this example. See Figure 11.10. 6 When fgets() starts reading lines from the file it picks up right after the line where the substring "eastern" was found. Figure 11.10. Marking a position with ftell(). Output from Example 11.9. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
11.2.6. Opening a URL for Reading You can open files with FTP or HTTP with the fopen() function. (Note: If opening the URL fails, check if the allow_url_fopen directive in the php.ini file is disabled.) Format resource fopen ( string filename, string mode [, bool use_include_path [, resource zcontext]] ) Example: $filehandle=fopen('http://www.site.com/'); $filehandle=fopen('ftp://username:password@ftp.wherever.com/pub/index' , 'r'); Example 11.10. Open a File Explanation 1 The file is the URL of a Web site. 2 The Web page is opened for reading and a filehandle is returned, called $fh. 3 The expression in the while loop uses the feof() function to check whether we are not yet at the end of the file. 4 The fgets() function reads 1024 bytes at a time from the page. The htmlspecialchars() function converts any special characters to HTML entities; for example, an & would become &amp and a < would become &lt, and so on. The output shown in Figure 11.11 is the actual source page (View Source) that was used to create the page. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 11.11. Viewing the contents of a Web page opened as a URL. 11.2.7. Reading from Files Without a Filehandle PHP provides functions that allow you to read the contents of a file without first opening a filehandle. The file_get_contents() Function—Reading the Whole File into a String An easy way to read the contents of an entire file is with the file_get_contents() function. You do not even need to get a filehandle, just pass the name of the file to the function and it will get the contents of the whole file and store it in a string. You can also start reading from a specified offset in the file and specify how many bytes you want to read. The file_get_contents() function will return FALSE, if it fails. The PHP manual suggests this as the most efficient way to read a file into a string. Format string file_get_contents ( string filename [, bool use_include_path [, resource context [, int offset [, int maxlen]]]] ) Example: $contents=file_get_contents("datafile.txt"); The file() Function—Reading the Whole File into an Array Without using a filehandle, you can read an entire file into an array with PHP’s file() function. The filename can be a full path, relative path, or even a URL (if each element of the array corresponds to a line in the file, with the newline still attached. The function returns FALSE if it fails. If you do not want the end-of-line character at the end of each of the array elements, use the rtrim() function, described in Chapter 6, “Strings.”[5] This function is identical to file_get_contents(), except that it returns the file in an array. [5] If PHP does not recognize the line endings (Macintosh), see the php.ini file to enable the auto_detect_line_endings runtime configuration option. Format array file ( string filename [, int use_include_path [, resource context]] ) Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Example 11.11. Parsing Lines "> Select a first name from the file.
$address,"19".$birth[2], '$'.number_format($salary,2))); 13 echo "$newstring"; 14 $count++; echo ""; } } 15 if($count==0){ echo "$first_name is not in the file."; } } ?> Explanation 1 The variable, $filename, is assigned the path to a file called data.file one level above the document root of the server in a directory called mydir. 2 The built-‐in file() function takes the filename as its argument (not a filehandle) and returns an array where each line is an element of the array. 3 The foreach loop cycles over each element of the array of lines, extracting the index and the value of the line. 4 By adding one to the value of $line_number, the index in the array, we can start the count at 1. This value will be placed in front of each line every time the loop body is executed. 5 Each line and its line number are displayed as shown in Figure 11.12. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 11.12. Using the file() function, creating line numbers. Using explode() and implode() After you have read in a line from a file or you get input from a file, you might want to break the lines into individual fields or create a string from an array of input items. This is where the array functions explode() and implode() can be useful, array functions discussed in Chapter 8, “Arrays.” Example 11.12 demonstrates how to use these functions. This example uses the text file called datebook.[6] Below are two lines from this file. Notice that the fields are separated by colons. [6] The datebook file can be found on the CD in the back of this book. Steve Blenheim:238-923-7366:95 Latham Lane, Easton, PA 83755:11/12/56:20300 Betty Boop:245-836-8357:635 Cutesy Lane, Hollywood, CA 91464:6/23/23:14500 Example 11.12. Code View: Parsing Lines
2 process_file(); } 3 function show_form(){ ?> Exploding and Imploding
} } ?> Explanation 1 If the form has not been submitted yet, the show_form() function will display it. 2 If the submit button was pressed, the form has already been filled out, and now it is time to process it. The process_file() function is called. 3 This is where the show_form() function is declared, which produces a very simple HTML form with one text box and a submit button. The user will type in the first name of someone from an external text file, called datebook. See Figure 11.13. 4 This is where the process_file() function is called. It will read a file into an array and break each line of the file into fields. If a line matches the first name of the input value typed into the form, that data for that person will be displayed. 5 The PHP file() function reads an entire file and assigns it to an array, where each line of the file is an element of the array. 6 The value of the variable called $first_name is what the user typed in the form and was sent via the POST method to this PHP program. Any whitespace is stripped out with the built-‐in trim() function. 7 The foreach loop iterates through each value in the array of lines that was created when the file() function read in the datebook file on line 5. 8 The explode() function splits up a string, $line, by a specified delimiter, in this case, by a colon. It creates an array where each of the elements represents the individual fields that were created. 9 The first element of the array called $fields[0] contains a first and last name. The explode() function will create a two-‐element array, called $fullname, consisting of a first and last name. 10 The strcasecmp() function compares two strings, case insensitive. If the value that came in from the form, $first_name, and the value of $fullname[0] are equal, then line 11 is entered. 11 The explode() function creates the $birth array by splitting $birthday; for example, 03/16/78, by slashes. 12, The implode() function joins or “glues” the array elements together into one 13 string, called "$newstring", displayed on line 13 and shown in Figure 11.14. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
13 string, called "$newstring", displayed on line 13 and shown in Figure 11.14. 14 A variable called $count will be incremented each time through this loop to keep track of the number of lines found matching the name compared in line 10. 15 If the value of the $count is 0, there were no matches, and the program displays a message saying so. Figure 11.13. The HTML form. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 11.14. After the lines in the file have been parsed. Output from Example 11.12. The readfile() Function—Reading and Writing a File The readfile() function reads from a file and writes it to the output buffer. It returns the number of bytes read from the file. If an error occurs, FALSE is returned and an error message is printed. Format int readfile ( string filename [, bool use_include_path [, resource context]] ) Example: readfile("myfile.txt"); Example 11.13. Reading and Outputting a File Reading and Outputting a File 1
?> Explanation 1 The HTML tag is used here so that when the file is displayed, the newlines will be preserved, as shown in Figure 11.16. 2 The readfile() function will read in the contents of data.file and send the output to the the output stream; for example, browser or terminal. It returns the number of bytes read. The function was called as @readfile() to suppress the printing of an error message if an error occurred. Figure 11.15. Reading a file and outputting its contents. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
11.2.8. Opening a File for Writing and Appending When you open a file for writing, the file is created if it does not exist, and truncated if it does. If you open a file for appending, the file will not be overwritten if it exists and the data will be appended to the bottom of the file. If it does not exist, opening for appending creates the file. To open a file for writing, the fopen() function returns a filehandle to either a text or binary file. Although UNIX and MacOS do not distinguish between text and binary files, Windows does. If a file is to be shared by multiple operating systems, it is safer to open it in binary mode in conjunction with one of the other modes. (As of PHP 4.3.2, the default mode is set to binary for all platforms that distinguish between binary and text mode.) UNIX and MacOS X represent the end-of-line character with \n, whereas Windows uses \r\n. If you use Windows, the "t" mode can be used with plain-text files to translate the \n to \r\n. Otherwise, the "b" mode should be used, which does not interpret data but treats it as just a series of bytes. If the file contents look weird when it is opened or you have a lot broken images, use the "b" mode. $handle = fopen("/home/marko/file.txt", "wb"); $handle = fopen("http://www.ellieq.com/", "w"); $handle = fopen("ftp://user:password@ellieq.com/myfile.txt", "a"); The fwrite() and fputs() Functions The fwrite() function writes a string text to a file and returns the number of bytes written. An alias for the fwrite() function is fputs(). It takes two arguments: the filehandle returned by fopen() and an optional length argument, how many bytes to write to the file. If it fails, fwrite() returns FALSE. The file_put_contents() Function The file_put_contents() also writes a string to a file and returns the number of bytes written, but does not require a filehandle. Otherwise it is the same as fwrite() and fputs(). Format int fwrite ( filehandle, string, [ int length] ) Example: $bytes=fwrite( $filehandle, "Peter Piper picked a peck of pickled peppers.\n"); $bytes=fwrite( $filehandle, "Jack in the Beanstalk", 4); Example 11.14. Open a File (Output: Contents of info.txt) Joe Shmoe Jr. 100 Main St. jshmoe@whatever.mil Major Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Explanation 1 A set of scalar variables are defined, the information that will be written to a file. 2 A string is created with each word separated by a tab. 3 Because the file must be a writeable file, it is stored outside the server’s root directory. It is located in the a directory called mydir, and the name of the file is info.txt. 4 The filehandle returned from fopen() is opened for writing. The "b" (binary) mode is recommended when using systems that differentiate between binary and text files; that is, Windows. 5 The fwrite() function writes the specified string, $outputstring to the filehandle, $filehandle. The number of bytes written are returned by the strlen() function. Appending to a File When a file is opened for appending, the write will start at the end of the file. If the file does not exist, it will be created. Example 11.15. Code View: Appending Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Explanation 1 The values of the variables are assigned to the variable, $outputstring. Each value is separated by a tab and the string ends with a newline. 2 The file info.txt is opened for appending, which means the internal file pointer will start writing at the end of the file, rather than the beginning. 3 If the fwrite() function fails, the program will produce an error. Otherwise, the string in $outputstring will be appended to the file. Output is shown in Figure 11.16. The line starting with Joe Doe has been appended. 4 The contents of the file are read and displayed. Figure 11.16. After writing and appending. Output from Example 11.15. Locking Files with flock() What if two or more customers are trying to write to a Web site at the same time? To prevent this, you can lock the file so that a user has exclusive access to it and then unlock it when he or she has finished using it. PHP supports a portable way of locking complete files with the flock() function. This is called advisory locking because all accessing programs have to use the same locking mechanism or it will not work. See Table 11.6 for a list of flock() operations. Table 11.6. flock() Operations (Constant) Numeric Operation Value Operation It Peforms LOCK_EX 2 Acquires an exclusive lock (writer). LOCK_NB 4 Nonblocking (no waiting) while the lock is being acquired. LOCK_SH 1 Acquires a shared lock (reader). LOCK_UN 3 Releases a lock (shared or exclusive). The flock() function uses a filehandle returned from the fopen() function. The lock can be released by fclose(), which is also called automatically when the script finished. The function returns TRUE on success or FALSE on failure. Whether or not this function works properly is entirely dependent on your operating system; for example, it is not supported on older systems like Windows 98 or for networked file systems (NFS), and so on. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Format bool flock ( resource handle, int operation [, int &wouldblock] ) Example 11.16. Code View: File Locking
11.2.9. File Checks Before performing operations on files or directories, it is a good practice to verify whether or not the file even exists, if it is readable, writable, executable, and so on. PHP provides a set of functions for testing the status of a file. See Table 11.7. Table 11.7. File Testing Functions Function Description file_exists() Checks if the file or directory exists. is_dir() Checks if the filename is a directory. is_file() Checks if the filename is a file. is_link() Checks if the filename is a symbolic link. is_readable() Checks if the file is readable. is_uploaded_file() Checks if the file was uploaded by an HTTP host. is_writable() Checks if the file is writable. is_writeable() An alias for is_writable. stat() Gives information about a file. The file_exists() Function The file_exists() function checks to see whether a file or directory exists. It returns TRUE if it does, and FALSE if it does not. Format bool file_exists ( string filename ); Example: if ( file_exists("filetest.php"); Example 11.17. Appending
?> Explanation 1 The file_exists() function checks to see if the image file assigned to $filename exists before displaying it. The is_file() Function The is_file() function checks to see if a file exists and is a regular file; that is, not a directory. It takes the name of the file as its argument and returns TRUE if the file is a regular file, and FALSE if it is not.[7] [7] Processing is faster if you use a relative path name rather than an absolute path. Format bool is_file ( string filename ) Example: if ( is_file("myfile.php"){ print "True"; } Example 11.18. Is it a Regular File? Explanation 1 The is_file() function not only checks to see if the file exists, but also if it is a regular file; that is, not a directory. 2 This line is displayed in Figure 11.17. The file c:\wamp\www is not a regular file. Please purchase PDF Split-Merge on www.verypdf.com to remove this watermark.
Figure 11.17. The file exist, but it is not a plain file. Output from Example 11.18. The is_readable() Function The is_readable() function checks to see if you can read from a file. It takes the filename as its argument and returns TRUE if the filename exists and is readable. If the PHP script is being executed by the server, the server’s permissions (usually limited) determine whether or not the PHP program can read from the file, and if it is being executed at the shell prompt, the permissions of the user running the script are the deciding factor. Normally, the file should be readable by others. Format bool is_readable ( string filename ); Example: if ( is_readable("file.txt")) { echo "File is readable";} Example 11.19. Is Readable?
The is_writable() Function When opening a file for writing, you might run into a problem with permissions if you are trying to put the file in a directory not accessible to the Web. Because the PHP script is executed on behalf of the server, it shares the same permissions. Normally, the server does not have world-write permissions turned on to prevent hackers from breaking into your site and causing havoc. The is_writable() (or is_writeable) function returns true if a file exists and is writable, and false if it is not. Format bool is_writable ( string filename ) Example: if (is_writable($filename)) {echo "$filename is writable";} Example 11.20. Appending