# V3547. AUTOSAR. Identifiers that start with '__' or '_[A-Z]' are reserved.

This diagnostic rule is based on the software development guidelines developed by AUTOSAR (AUTomotive Open System ARchitecture).

As defined by the C++ standard, macro names and identifiers that contain the '__' sequence anywhere or begin with '_[A-Z]' are reserved for use in the language and standard library implementation. The same rule applies to the C language as well, except that the '__' sequence should be at the beginning of a reserved identifier.

Declaring such identifiers outside the standard library may cause problems. For example, this code:

    #define _BUILTIN_abs(x) (x < 0 ? -x : x)
    #include <cmath>
    int foo(int x, int y, bool c)
    {
      return abs(c ? x : y)
    }

may change the behavior of the 'abs' function if this function is implemented through the use of the compiler's built-in (intrinsic) function as follows:

    #define abs(x) (_BUILTIN_abs(x))

This diagnostic is classified as:

AUTOSAR-A17.0.1