PHP Set 6

Question 1

How can you read a file in PHP and what is the syntax?

Answer 1

readfile() function allows you to read a file and write it to the output buffer
Syntax:
readfile(string $filename, bool $use_include_path=false, resource $context): int | false

Question 2

What does the readile function return?

Answer 2

Returns the number of bytes read from the file on success or false on failure

Question 3

How do you open a file and what is the syntax?

Answer 3

Using the fopen() function
Syntax:
fopen(string $filename, string $mode, bool $use_include_path=false, resource $context): resource | false

Question 4

What does the fopen function return?

Answer 4

Returns a file pointer resource on success or false on failure

Question 5

What are the possible modes you can select when opening a file?

Answer 5

1. ‘r’ is to open for reading only
2. ‘r+’ is to open for reading and writing
3. ‘w’ is to open for writing only
4. ‘w+’ is to open for reading and writing
5. ‘a’ is to open for writing only
6. ‘a+’ is to open for reading and writing
7. ‘x’ is to create and open for writing only
8. ‘x+’ is to create and open for reading and writing
9. ‘c’ is to open the file for writing only
10. ‘c+’ is to open the file for reading and writing

Question 6

What is the difference between ‘w’, ‘a’, ‘x’, and ‘c’ file open modes since they are all used for writing only?

Answer 6

w places the file pointer at the beginning of the file and truncates the file to zero length before writing. If the file does not exist it will try to create it

a places the file pointer at the end of the file. fseek function has not effect as writes are always appended. If the file does not exist it will try to create it

x places the file pointer at the beginning of the file. If the file already exists the open call will fail and an E_WARNING error will be generated

c positions the file pointer at the beginning of the file. It will not truncate it or throw an error if the file already exists.

Question 7

What function is used to read from an open file and what is the syntax?

Answer 7

Use the fread() function to read up to a specified number of bytes from the stream created by fopen()
Syntax:
fread(resource $stream, int $length): string | false

Question 8

What does the fread function return?

Answer 8

Returns the read data as a string on success or false on failure

Question 9

How can you get the size of a file in bytes?

Answer 9

Using the filesize(string $filename) function

Question 10

How do you close a file?

Answer 10

Using the fclose(resource $stream) function

Question 11

What does the fgets function do and what is its syntax?

Answer 11

It is used to read a single line from an opened file
Syntax:
fgetsIresource $handle, int $length=?): string | false

Question 12

What does the fgets function return?

Answer 12

Returns a string of up to length-1 bytes read from the file on success or false on failure

Question 13

What is the difference between fread and fgets?

Answer 13

fread is a binary-safe file read and reads up to the number of bytes that must be specified.
fgets gets a line from a file pointer, it reads a line and stops when it encounters a newline if a length is not provided

Question 14

What does the fclose function return?

Answer 14

Returns true on success or false on failure

Question 15

What does the feof function do and what is its syntax?

Answer 15

Checks if the end of file has been reached
Syntax:
feof(resource $stream): bool

Question 16

What does the feof function return?

Answer 16

Returns true if EOF has been reached or an error occurs. Returns false otherwise

Question 17

What function is used to write to a file and what is its syntax?

Answer 17

Use the fwrite() function to write to a file open for writing
Syntax:
fwrite(resource $stream, string $string, int $length): int | false

Question 18

What does the fwrite function return?

Answer 18

Returns the number of bytes written on success or false on error

Question 19

What do you need to do in order to enable uploading files to a web server?

Answer 19

Configure the php.ini file and specify file_uploads = on
Create an HTML form with a file upload input
On the server side, use the move_uploaded_file function to move the uploaded file to a space on the server’s hard disk

Question 20

Why should you use filters in PHP?

Answer 20

Many web application receive external input and you should always validate external data before using it

Question 21

What are the 2 types of filters?

Answer 21

1. Validating data: Determines if data is in the proper form and meets certain qualifications
2. Sanitizing data: Removes illegal characters from the data so it may alter the data

Question 22

What function is used to filter input and what is the syntax?

Answer 22

filter_var() filters a variable with a specified filter
Syntax:
filter_var($var, filtername, options)
var is the variable to filter
filtername is the ID or name of the filter to use (FILTER_DEFAULT by default which is not filtering)
options specifies one or more flags to use

Question 23

What does the filter_var function return?

Answer 23

Returns the filtered data on success or false on failure

Question 24

What are the possible validate filters available?

Answer 24

1. FILTER_VALIDATE_BOOL
2. FILTER_VALIDATE_BOOLEAN
3. FILTER_VALIDATE_DOMAIN
4. FILTER_VALIDATE_EMAIL
5. FILTER_VALIDATE_FLOAT
6. FILTER_VALIDATE_INT
7. FILTER_VALIDATE_IP
8. FILTER_VALIDATE_MAC
9. FILTER_VALIDATE_URL
10. FILTER_VALIDATE_REGEXP

Question 25

What are the possible sanitize filters?

Answer 25

1. FILTER_SANITIZE_EMAIL
2. FILTER_SANITIZE_ENCODED
3. FILTER_SANITIZE_MAGIC_QUOTES
4. FILTER_SANITIZE_ADD_SLASHES
5. FILTER_SANITIZE_NUMBER_FLOAT
6. FILTER_SANITIZE_NUMBER_INT
7. FILTER_SANITIZE_SPECIAL_CHARS
8. FILTER_SANITIZE_FULL_SPECIAL_CHARS
9. FILTER_SANITIZE_STRING
10. FILTER_SANITIZE_STRIPPED
11. FILTER_SANITIZE_URL
12. FILTER_UNSAFE_RAW

Question 26

What are the options available for FILTER_VALIDATE_URL?

Answer 26

1. FILTER_FLAG_SCHEME_REQUIRED: Ensures URL is RFC compliant
2. FILTER_FLAG_HOST_REQUIRED: Ensures URL includes host name
3. FLITER_FLAG_PATH_REQUIRED: Ensures the URL has a path after the domain name
4. FILTER_FLAG_QUERY_REQUIRED: Ensures the URL has a query string attched