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V3120. Potentially infinite loop. The v…
Analyzer Diagnostics
General Analysis (C++)
General Analysis (C#)
General Analysis (Java)
Diagnosis of micro-optimizations (C++)
Diagnosis of 64-bit errors (Viva64, C++)
MISRA errors
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Additional information
Contents

V3120. Potentially infinite loop. The variable from the loop exit condition does not change its value between iterations.

Nov 14 2016

The analyzer detected a potentially infinite loop with its exit condition depending on a variable whose value never changes between iterations.

Consider the following example:

int x = 0;
while (x < 10)
{
  Do(x);
}

The loop's exit condition depends on variable 'x' whose value will always be zero, so the 'x < 10' check will always evaluate to "true", causing an infinite loop. A correct version of this code could look like this:

int x = 0;
while (x < 10)
{
  x = Do(x);
}

Here is another example where the loop exit condition depends on a variable whose value, in its turn, changes depending on other variables that never change inside the loop. Suppose we have the following method:

int Foo(int a)
{
  int j = 0;
  while (true)
  {
    if (a >= 32)
    {
      return j * a;
    }

    if (j == 10)
    {
      j = 0;
    }
    j++;
  }
}

The loop's exit condition depends on the 'a' parameter. If 'a' does not pass the 'a >= 32' check, the loop will become infinite, as the value of 'a' does not change between iterations. This is one of the ways to fix this code:

int Foo(int a)
{
  int j = 0;
  while (true)
  {
    if (a >= 32)
    {
      return j * a;
    }

    if (j == 10)
    {
      j = 0;
      a++; // <=
    }
    j++;
  }
}

In the fixed version, the local variable 'j' controls how the 'a' parameter's value changes.

This diagnostic is classified as:

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