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    <p>Compiler output is expected to be different, sometimes dramatically different for the same source. In the same way that a toyota and a honda are different. Four wheels and some seats sure, but more different than the same when you look at the details.</p> <p>Likewise the same compiler with different compiler options can and often will produce dramatically different output for the same source code. Even for what appears to be simple programs.</p> <p>In the case of your simple program, which actually does not do anything (code does not affect the input, nor output, nor anything outside the function), a good optimized compiler will result in nothing but main: with a return of some random number since you didnt specify the return value. Actually it should give a warning or error. This is the biggest problem I have when I compare compiler output is making something simple enough to see what they are doing but something complicated enough that the compiler does more than just pre-compute the answer and return it.</p> <p>In the case of x86, which I assume is what you are talking about here, being microcoded these days there is really no answer for good code vs bad code, each family of processor they change the guts around and what used to be fast is slow and what is now fast is slow on the old processor. So for compilers like gcc that have continued to evolve with the new cores, the optimization can be both generic to all x86es or specific to a particular family (resulting in different code despite max optimization).</p> <p>With your new interest in disassembling, you will continue to see the similarities and differences and find out just how many different ways the same code can be compiled. the differences are expected, even for trivial programs. And I encourage you to try as many compilers as you can. Even in the gcc family 2.x, 3.x, 4.x and the different ways to build it will result in different code for what might be though thought of as the same compiler.</p> <p>Good vs bad output is in the eyes of the beholder. Folks that use debuggers will want their code steppable and their variables watchable (in written code order). This makes for very big, bulky, and slow code (particularly for x86). And when you compile for release you end up with a completely different program which you have so far spent zero time debugging. Also optimizing for performance you take a risk of the compiler optimizing out something you wanted it to do (your example above, no variable will be allocated, no code to step through, even with minor optimization). Or worse, you expose the bugs in the compiler and your program simply doesnt work (this is why -O3 is discouraged for gcc). That and/or you find out the large number of places in the C standard whose interpretation is implementation defined. </p> <p>Unoptimized code is easier to compile, as it is a bit more obvious. In the case of your example the expectation is a variable is allocated on the stack, some sort of stack pointer arrangement set up, the immediate 1 is eventually written to that location, stack cleaned up and function returns. Harder for compilers to get wrong and more likely that your program works as you intended. Detecting and removing dead code is the business of optimization and that is where it gets risky. Often the risk is worth the reward. But that depends on the user, beauty is in the eye of the beholder.</p> <p>Bottom line, short answer. Differences are expected (even dramatic differences). Default compile options vary from compiler to compiler. Experiment with the compile/optimization options and different compilers and continue to disassemble your programs in order to gain a better education about the language and the compilers you use. You are on the right track so far. In the case of the borland output, it detected that your program does nothing, no input variables are used, no return variables are used, nor related to the local variables, and no global variables or other external to the function resources are used. The integer a and the assignment of an immediate are dead code, a good optimizer will essentially remove/ignore both lines of code. So it bothered to setup a stack frame then clean it up which it didnt need to do, then returned. gcc looks to be setting up an exception handler which is perfectly fine even though it doesnt need to, start optimizing or use a function name other than main() and you should see different results.</p>
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    1. COWow, um just wow thanks that helps a lot. :-) I'll let the question stay open but so far you get the check and at least one upvote :-).
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    2. COdont rush to check off an answer, give it a few days no matter what. No question that there are others out there with checkworthy answers, leave it open so they can have a chance.
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    3. COThanks for the upvote, and thanks for the question.
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