# V2604. MISRA. Features from <stdarg.h> should not be used.

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

This rule only applies to C. You shouldn't use the '<stdarg.h>' header file that includes the 'va_list' type , as well as macros 'va_arg', 'va_start', ' va_end' and 'va_copy'. They are necessary for working with functions with a variable number of arguments. However, the improper use of the '<stdarg.h>' header file often causes undefined behavior.

Look at the example:

    #include <stdint.h>
    #include <stdarg.h>

    void foo(va_list args)
    {
      double y;
      y = va_arg(args, int);
    }

    void bar(uint16_t count, ...)
    {
      uint16_t x;
      va_list ap;
      va_start (ap, count); // <=
      x = va_arg (ap, int);
      foo(ap);
      x = va_arg (ap, int);
    }

    void baz(void)
    {
      bar(1.25, 10.07);
    }

The code above demonstrates several problems that can lead to undefined behavior. Note: the list below contains only the issues that relate to this diagnostic:

- The 'va_start' macro is called in the 'bar' function. However, the 'va_end' macro is not called.
- The 'va_arg' macro is applied to the same 'va_list' object in different functions. The developer cannot control the what state the argument list is in as well as the number of elements that were extracted from it after passing the 'ap' variable to the function. Hence the problem.
- The 'bar' function with the arguments of the 'double' type is called in the 'baz' function, although the 'bar' function expects 'int'. Calling the 'bar' function can lead to data loss.

This diagnostic is classified as:

MISRA-C-2012-17.1 MISRA-C-2023-17.1