Coding - files

Question 1

What do fstreams provide?

Answer 1

Fstreams provide a series of classes for file input and output. Included in the  library.
#include

Question 2

What are the two classes of file input and output?

Answer 2

std: :ofstream file output;
std: :ifstream file input;

Question 3

How do you use a file stream?

Answer 3

• Declare the type of stream

- Call open() on the file stream

Question 4

Give an example statement of inputting a file stream.

Answer 4

fileInput.open (“some.txt”, std::fstream::in);

Question 5

What is the first argument within opening a file?

Answer 5

The first argument is the file path

• Can be absolute: “/Users/sj4-hunt/Documents/IAP-2018- 2019/sounds/bd.wav”
• Or relative: “text.txt”

Question 6

How are folder paths separated?

Answer 6

Folder paths are separated with the / symbol

Question 7

What is the second argument within opening a file?

Answer 7

The second argument is file options:
- The most commonly used ones are Std::fstream::in
and Std::fstream::out

Question 8

Before trying to read or write a file what must we do?

Answer 8

We must first check that has open correctly

- Use .is_open()

Question 9

Give an example of checking if the file works properly.

Answer 9

if (fileInput.is_open()) { //opened ok!
}
else {
std::cout << "error opening file \n";
}

Question 10

What are the reasons for file errors?

Answer 10

• File does not exist
• Incorrect permissions
• Not enough memory

Question 11

What does the eof() method stand for?

Answer 11

End of file

• returns false if there is still data in the file
• returns true when the file has been read

Question 12

What do we do once we have finished using a file?

Answer 12

We need to call close() on it.

- fileInputStream.close();

Question 13

What is the getLine function used for?

Answer 13

Reading a single line from the file up to a ‘\n’ character.

Question 14

What are the two ways of passing values to a function?

Answer 14

By copy:
void copyValue (int number);

By reference:
void referenceValue (int & number);

Question 15

What does a reference mean?

Answer 15

When we pass by reference we pass the actual variable

• This allows us to update the value of the variable passed in:
• Variables passed by reference are given the & symbol

Question 16

When should you pass by reference?

Answer 16

• When you want to be able to write to the variable
• When you want to have multiple return types
• Pass large data structures that would be expensive to copy

Question 17

What is the order to writing a file?

Answer 17

1. Open file
2. Check file is open
3. Write contents
4. Close file

Question 18

Give an example of the whole file writing process.

Answer 18

std::ofstream outputStream
outputStream.open("file.txt", std::ofstream::out);
if (outputStream.is_open()) {
outputStream << 60 << "\n";
}
outputStream.close();

Question 19

How do you write data to a file?

Answer 19

outputStream &laquo_space;” “; OR
outputStream &laquo_space;10; //int OR
outputStream &laquo_space;0.01; //float

Question 20

Give an example of the reading process.

Answer 20

std: :ifstream myFile(“thisis.txt”);
std: :string text;

while(myFile >> text)
{
    std::cout << text << "\t";
}