A0-1-1 - Unofficial Autosar C++ Guidelines Reference

Rule A0-1-1 (required, implementation, automated)

A project shall not contain instances of non-volatile variables being given values that are not subsequently used.

Rationale

Known as a DU dataflow anomaly, this is a process whereby there is a data flow in which a variable is given a value that is not subsequently used. At best this is inefficient, but may indicate a genuine problem. Often the presence of these constructs is due to the wrong choice of statement aggregates such as loops.

See: DU-Anomaly.

Exception

Loop control variables (see Section 6.6.5) are exempt from this rule.

Example

//% $Id: A0-1-1.cpp 289436 2017-10-04 10:45:23Z michal.szczepankiewicz $
#include <array>
#include <cstdint>
std::uint8_t Fn1(std::uint8_t param) noexcept
{
    std::int32_t x{
        0}; // Non-compliant - DU data flow anomaly; Variable defined,
            // but not used
    if (param > 0)
    {
        return 1;
    }
    else
    {
        return 0;
    }
}
std::int32_t Fn2() noexcept
{
    std::int8_t x{10U}; // Compliant - variable defined and will be used
    std::int8_t y{20U}; // Compliant - variable defined and will be used
    std::int16_t result = x + y; // x and y variables used

    x = 0; // Non-compliant - DU data flow anomaly; Variable defined, but x is
           // not subsequently used and goes out of scope
    y = 0; // Non-compliant - DU data flow anomaly; Variable defined, but y is
           // not subsequently used and goes out of scope
    return result;
}
std::int32_t Fn3(std::int32_t param) noexcept
{
    std::int32_t x{param +
        1}; // Compliant - variable defined, and will be used in
            // one of the branches
            // However, scope of x variable could be reduced
    if (param > 20)
    {
        return x;
    }
    return 0;
}
std::int32_t Fn4(std::int32_t param) noexcept

{
    std::int32_t x{param +

        1}; // Compliant - variable defined, and will be used in
            // some of the branches

    if (param > 20)
    {
        return x + 1;
    }
    else if (param > 10)
    {
        return x;
    }
    else
    {
        return 0;
    }
}
void Fn5() noexcept
{
    std::array<std::int32_t, 100> arr{};
    arr.fill(1);

    constexpr std::uint8_t limit{100U};
    std::int8_t x{0};
    for (std::uint8_t i{0U}; i < limit; ++i) // Compliant by exception - on the
                                             // final loop, value of i defined will
                                             // not be used
    {
        arr[i] = arr[x];
        ++x; // Non-compliant - DU data flow anomaly on the final loop, value
             // defined and not used
    }

}

Unofficial Autosar C++ Guidelines Reference

Rationale

Exception

Example

See also