Re:Main is usually a function, so when is it not? (2015)
by microcolonel on Sunday September 10, 2017 @03:30PM
(#15213866)
I like to start with the assembler, then just tell people that high level languages are fancy assemblers. Some of them restrict you to using the designer's favourite macros, some of them allow you to build on highly general tools at approximately the lowest level, but ultimately all computer programming languages are fancy macro assembler syntaxes.
Re:Main is usually a function, so when is it not? (2015)
by tomjakubowski on Sunday September 10, 2017 @05:35PM
(#15214424)
This is an OK mental model until a wholly compliant C or C++ compiler blows it all to smithereens with an optimization exploiting UB.
You gotta write C or C++ for the abstract machine defined by the standards. Thinking about C in terms of some concrete assembly language or architecture can be problematic.
Re:Main is usually a function, so when is it not? (2015)
by microtherion on Sunday September 10, 2017 @06:18PM
(#15214596)
> "What if you cast a string pointer to a function and called it! Huh?" and I explain that is perfectly legal C
I would argue that it's less than "perfectly" legal: The C standard lists it as a "common extension":
J.5.7 Function pointer casts
A pointer to an object or to void may be cast to a pointer to
a function, allowing data to be invoked as a function
Re:Main is usually a function, so when is it not? (2015)
by insulanus on Monday September 11, 2017 @05:27PM
(#15222514)
That's a good point, but the long running (although shrinking) gap between what the standard recommends, vs. what you can do with real compilers is one of the reasons that coding in C can be so error-prone.
I find these "hey there is this language called C and you can do some really weird stuff in it!" articles humorous because from the beginning of time there have been people who are fascinated by this aspect of the C language and gave rise to the whole obfuscated C contest thing.
The idea that a symbol references an address and its type is only a convenience in the source code always messes people up. When I've taught C to people there is always that one person who says "What if you cast a string pointer to a function and called it! Huh?" and I explain that is perfectly legal C and has been exploited for years and you can practically see their brain change conceptual planes in mid-air :-)