Is Your C/C Code Making Unwarranted Assumptions?

Demonstrating Unwarranted Assumptions in C/C

How can this educational tool be improved?

To enhance the effectiveness of this tool, consider the following suggestions:

• Incorporate conditional compilation: Use conditional compilation to test assumptions based on specific platform characteristics. For example, if your test program relies on specific platform-dependent features, you can use #ifdef or #if __GNUC__ to tailor the tests to different compiler environments.

• Expand the test cases: Include a wider variety of test cases to cover more common assumptions made by programmers. Examples could include:

  • "Floating-point arithmetic is associative"
  • "The size of a void* is the same as the size of the smallest addressable unit"
  • "The sign of a negative number is always -"
• Automate the tests: Create a script or automated tool to execute the tests and collect the results across different platforms. This will streamline the testing process and make it easier to maintain the database of platform differences.

Which tests would be good and how should they look like?

1. Character Assumptions:

• Test: Verify that 'A' == 65 on all platforms.

• Code:

  <code class="c">EXPECT("00 we have ASCII",('A'==65));</code>

• Test: Check if the assumption that 'a' < 'A' is valid.

• Code:

  <code class="c">EXPECT("02 big letters come before small letters",('A'<'a'));

• Test: Test if the size of char is always 8 bits.

• Code:

  <code class="c">EXPECT("04 a char is 8 bits",CHAR_BIT==8);

2. Integer Assumptions:

• Test: Examine if the assumption that integers use two's complement representation and wrap around is valid.

• Code:

  <code class="c">EXPECT("06 integers are 2-complement and wrap around",(int_max+1)==(int_min));

• Test: Check if the assertion that the size of an int is the same as the size of a void* is true on all platforms.

• Code:

  <code class="c">EXPECT("05 int has the size of pointers",sizeof(int)==sizeof(void*));

3. Pointer Assumptions:

• Test: Verify that sizeof(void*) is always greater than or equal to sizeof(void(*)()).

• Code:

  <code class="c">EXPECT("10 void* can store function pointers",sizeof(void*)>=sizeof(void(*)()));</li>
  </ul>
  <p><strong>4. Execution Assumptions:</strong></p>
  <ul>
  <li>
  <strong>Test:</strong> Test if the stack always grows downwards.</li>
  <li>
  <p><strong>Code:</strong></p>
  <blockquote><pre class="brush:php;toolbar:false"><code class="c">EXPECT("12 the stack grows downwards",check_grow(5,0)<0);</code>

• Test: Examine the assumption that the evaluation of expressions is always left to right.

• Code:

  <code class="c">EXPECT("00 we have ASCII",('A'==65));</code>

Would you run the tests on the platforms you can get your hands on and post the results?

We encourage community participation in testing the assumptions on different platforms. Please share your results along with the following information:

• Platform details (operating system, compiler version, architecture)
• Any differences observed from the expected results
• Why the differences might occur (e.g., compiler optimizations, platform-specific implementation)

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