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Home » Tip Bank » C++
Language: C++
Expertise: Intermediate
Feb 13, 2006

Beware of Using Loop Variables Outside the Loop

People using loop variables in compilers like VC++ 6.0 are acccustomed to using loop variables after the loop. For example, take a look at the following code:

for (int i=0; i<100; i++) 
{
    // ...
}

// 'i' used after the loop.
std::cout << i;
This code would happily compile under VC++ 6.0 or lower. But this code is in violation of C++ standards which explicitly state that the scope of the loop control variable i is limited to within the loop, after which it is destroyed.

This rule has been correctly implemented from VC++ 7.0 onwards. It is also correctly implemented in gcc. So if you're migrating a project from VC++ 6.0 to 7.0 or to gcc, this discrepancy will cause compilation errors.

So, avoid using the loop variables outside the loop.

C.V. Ram Narayanan Sastry
 
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