Yesterday, I had an interview.

Continental Interview Question for Software Engineer / Developers

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Yesterday, I had an interview. There they asked me when the code optimization happens? Say,

int abc;//Global variable
abc = 3;
if(abc == 3)
{
printf("abc will be always 3");
}
else
{
printf("This will never executed");
}
Now the question is when the optimization happens? A... At Run time B... At compile time. I answered at compile time... To me I thought, compiler checks for volatile keyword at compile time. If the variable is not declared as volatile then it optimizes the code. But, when the compiler comes to know that, this variable is never ever going to be other than 3? If it is at run-time, then when compiler comes to know that variable is never ever going to be other than 3? Because if the variable is going to be changed after this part of the code executed. Please clear my doubt
- rasmiranjanbabu February 04, 2012 in India | Report Duplicate | Flag | PURGE
Continental Software Engineer / Developer C

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Country: India
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of 2 vote

You're definitely correct that in C or C++ code, the optimization will be done at compile time if it is done at all. In your particular situation, the compiler definitely could decide to perform the optimization.

- eugene.yarovoi February 04, 2012 | Flag Reply

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of 1 vote

Optimizations can never be done during run time.

- Anony February 04, 2012 | Flag Reply

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of 0 votes

Not in C, that is.

- eugene.yarovoi February 04, 2012 | Flag

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of 0 vote

The optimization should happen during compile time, with respect to the above chunk of code.
This is because
1) Other than " abc = 3 " the code is not being altered anywhere
2) Also you don't see any statement like " abc = RHS " where you are trying to assign a new value at run time.

Hece the compiler is very sure that " Else " part never gets executed. Hence code optimization should happen @ compile time.

- Vijay Rajanna February 06, 2012 | Flag Reply

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of 0 vote

It says 'abc' is a global variable, which could be externed in other file and modified over there??
so i don't think compiler can optimize this particular case..

plz correct if wrong..

- Anurag February 24, 2012 | Flag Reply

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of 0 vote

It says 'abc' is a global variable, which could be externed in other file and modified over there??
so i don't think compiler can optimize this particular case..

plz correct if wrong..

- Anurag February 24, 2012 | Flag Reply

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of 0 votes

correct. In this case compiler is not sure if the variable is mopdified in any other translation unit.

- Ananta March 10, 2012 | Flag

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of 0 votes

Oh...I interpreted all this code to be part of a method, with abc being a local variable.

- eugene.yarovoi June 19, 2012 | Flag

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