Runtime error handling in Compiler Design - Step-by-Step Execution

Concept Flow - Runtime error handling

Program starts

↓

Execute instructions

↓

Runtime error occurs?

No→Continue execution

Yes↓

Error detected by runtime system

↓

Invoke error handler

↓

Handle error: report, recover, or terminate

↓

Program ends or resumes

The program runs instructions until a runtime error occurs, which is detected and handled by the runtime system to either recover or stop the program.

Execution Sample

Compiler Design

start program
execute instruction 1
execute instruction 2
runtime error occurs
invoke error handler
handle error
end or resume

This shows the steps from program start to error detection and handling during execution.

Analysis Table

Step	Action	Error Detected?	Handler Invoked?	Outcome
1	Start program	No	No	Program running
2	Execute instruction 1	No	No	Instruction successful
3	Execute instruction 2	No	No	Instruction successful
4	Execute instruction 3	Yes (e.g. divide by zero)	Yes	Error handler starts
5	Error handler processes error	Yes	Yes	Error reported and handled
6	Decide to recover or terminate	Yes	Yes	Program resumes or ends
7	If recovered, continue execution	No	No	Program continues
8	If terminated, stop program	No	No	Program ends

💡 Execution stops or continues based on error handler decision after runtime error detection

State Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	Final
Program State	Running	Running	Error Detected	Handled (Recovered or Terminated)	Ended or Running
Error Flag	False	False	True	Handled	Cleared or Active
Instruction Pointer	1	3	Paused at 3	Moved or Stopped	Next or None

Key Insights - 3 Insights

Why does the program stop executing normal instructions after a runtime error?

Because the runtime system detects the error (see step 4 in execution_table) and immediately invokes the error handler to manage the problem before continuing.

Can the program continue running after a runtime error?

Yes, if the error handler recovers from the error (step 6 and 7), the program can resume normal execution; otherwise, it terminates.

What role does the error flag variable play during runtime error handling?

The error flag indicates whether an error has occurred (see variable_tracker). It changes from False to True when an error is detected and helps the runtime system decide to invoke the handler.

Visual Quiz - 3 Questions

Look at the execution_table at step 4. What happens when a runtime error is detected?

A The program terminates instantly

B The program continues without interruption

C The error handler is invoked immediately

D The error is ignored

💡 Hint

Check the 'Handler Invoked?' and 'Outcome' columns at step 4 in execution_table

According to variable_tracker, what is the value of 'Error Flag' after step 3?

A False

B True

C Handled

D Paused

💡 Hint

Look at the 'Error Flag' row under 'After Step 3' in variable_tracker

If the error handler decides to recover, which step in execution_table shows the program continuing execution?

A Step 5

B Step 7

C Step 8

D Step 4

💡 Hint

Refer to the 'Outcome' column for step 7 in execution_table

Concept Snapshot

Runtime error handling:
- Happens during program execution when unexpected errors occur
- Runtime system detects errors and sets an error flag
- Error handler is invoked to manage the error
- Handler can report, recover, or terminate the program
- Program may resume or stop based on handler decision

Full Transcript

Runtime error handling occurs when a program encounters an unexpected problem while running, such as dividing by zero or accessing invalid memory. The runtime system detects this error and sets an error flag. It then invokes an error handler to manage the situation. The handler can report the error, try to recover so the program continues, or terminate the program to prevent further issues. The execution flow pauses at the error, and depending on the handler's decision, the program either resumes normal execution or ends. This process ensures programs handle errors gracefully during runtime.