# V2592. MISRA. An identifier declared in an inner scope should not hide an identifier in an outer scope.

This diagnostic rule is based on the MISRA (Motor Industry Software Reliability Association) software development guide.

This rule only applies to programs written in C. An identifier declared in an inner scope and an identifier declared in an outer scope should have different names. Otherwise, an identifier declared in the inner scope hides the one from the outer scope. This can lead to confusion or a software error.

Such a name collision may result in a logical error as in the example below:

    int foo(int param)
    {
      int i = 0;
      if (param > 0)
      {
        int i = var + 1;
      }
      return i;
    }

The 'foo' function receives a positive parameter value. At first glance the function seems to return this value increased by '1'. However, that does not happen. In fact, the function always returns '0'. To prove that let's change the identifiers names:

    int foo(int param)
    {
      int i_outer = 0;
      if (param > 0)
      {
        int i_inner = var + 1;
      }
      return i_outer;
    }

Now it is clear that the value of the 'i' variable in the 'if' branch does not affect the result of the 'foo' function. The 'i' identifier ('i_inner') in the inner scope hides the 'i' identifier ('i_outer') from the outer scope. An error occurs.

This diagnostic is classified as:

MISRA-C-2012-5.3 MISRA-C-2023-5.3