# V2616. MISRA. All conditional inclusion preprocessor directives should reside in the same file as the conditional inclusion directive to which they are related.

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

Conditional compilation directives '#else', '#elif' and '#endif' must be in the same file as the '#if', '#ifdef' or '#ifndef' to which they refer. Non-compliance with this rule makes code more difficult to read. Besides, this increases the probability of a mistake when you edit and maintain code.

Note: it is impossible to make this error in modern compilers. Incorrect use of conditional compilation directives in these compilers leads to compile-time errors.

Look at the example:

    #define Check_A 10

    #ifdef Check_A        // <=
    #if Check_A > 5
    static int a = 5;
    #elif Check_A > 2
    static int a = 2;
    #else
    static int a = 0;
    #endif                // <=

    int main(void)
    {
      return a;
    }

In the first example a nested condition that consists of '#ifdef' and '#if' is used. At the end of the fragment the second conditional compilation directive ('#if') is closed, but '#ifdef' remains open. This can create incorrect code.

Look at another example:

    /* File.h */
    #ifdef Check_B
    #include "SomeOtherFile.h"    // <=
    /* End of File.h */

In this example the conditional compilation directive is not closed. If you include this file in others using the '#include' preprocessor directive, this can lead to subtle errors.

This diagnostic is classified as:

MISRA-C-2012-20.4 MISRA-C-2023-20.4 MISRA-CPP-2008-16.1.2