Data hiding in C++ - Step-by-Step Execution

Concept Flow - Data hiding

Start Program

↓

Define Class with private data

↓

Create Object

↓

Try to access private data

↓

Use public methods to access data

↓

Data accessed safely

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End Program

Data hiding means keeping data private inside a class and only allowing access through public methods.

Execution Sample

C++

class Box {
private:
  int length;
public:
  void setLength(int l) { length = l; }
  int getLength() { return length; }
};

Defines a class with a private variable and public methods to set and get its value.

Execution Table

Step	Action	Variable/Member	Value	Access Allowed?	Output
1	Create object b	b	Box instance	N/A	N/A
2	Try to access b.length directly	b.length	undefined	No	Error: private member
3	Call b.setLength(10)	length	10	Yes	N/A
4	Call b.getLength()	length	10	Yes	10
5	End program	N/A	N/A	N/A	N/A

💡 Direct access to private member length is denied; access through public methods allowed.

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
length	undefined	10	10	10

Key Moments - 2 Insights

Why can't we access the private variable 'length' directly from the object?

Because 'length' is declared private, direct access is blocked by the compiler as shown in step 2 of the execution_table.

How do we change or read the private variable 'length'?

We use public methods like setLength and getLength to safely modify and access 'length', as shown in steps 3 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what happens when we try to access b.length directly at step 2?

A Access is allowed and value is shown

B Value is zero by default

C Access is denied with an error

D Program crashes silently

💡 Hint

Check step 2 in execution_table where access is marked 'No' and output shows an error.

At which step does the private variable 'length' get its value set?

A Step 3

B Step 2

C Step 1

D Step 4

💡 Hint

Look at step 3 where setLength(10) is called and length changes to 10.

If we remove the 'private:' keyword, what would change in the execution_table?

A Step 4 would return zero

B No change at all

C Step 2 would allow access to length directly

D Step 3 would fail

💡 Hint

In C++, members of a class are private by default, so removing the explicit 'private:' keyword does not change the access level of 'length'.

Concept Snapshot

Data hiding in C++:
- Use 'private:' to hide data members
- Access hidden data only via public methods
- Prevents direct external access
- Protects data integrity
- Example: private int length; public set/get methods

Full Transcript

Data hiding means keeping some data inside a class private so that no one outside the class can change or see it directly. In C++, we use the keyword 'private:' to hide variables. To work with these hidden variables, we create public methods like setLength and getLength. When we try to access a private variable directly, the program gives an error. But using public methods, we can safely change or read the data. This protects the data from accidental or wrong changes. The example shows a class Box with a private variable length. We create an object b of Box. Trying to access b.length directly fails. But calling b.setLength(10) sets the value, and b.getLength() returns 10. This is how data hiding works to keep data safe inside classes.