lesson outline

to remember

compiling

• as said last week, make isn’t actually the compiler. instead, the compiler is a program called clang. make is just a quicker way to call clang that automatically populates the parameters for you, because clang commands actually get pretty long.

  • an alternative to clang is gcc
  • when you get errors when you run make, it’s generally actually clang whomst is throwing those errors

• why? because you need to link in any libraries that you’re using by naming them in the clang command:

  • [?] if it’s linking in “the actual 0s and 1s” of the library function, then does that mean it’s getting the definition of the function and making the library function part of your code… or does that instead mean that the process of compiling involves running the code, and that it runs the compiled library function whenever it gets to the point in your code where it’s called….?

• why didn’t we have to include a link like -lstdio too? well, stdio is just special, since it’s SO universally used; the compiler already links it by default without having to type it out.

• note the difference between an “undefined reference” due to “linker command failed” with clang, and the other kind of error make will give if you didn’t include the right header. “linker command failed” doesn’t mean that anything is wrong with your code itself.

• 4 steps that happen when you compile code:

  1. preprocessing

     • [?] do preprocessing directives need to be at the top of the file in order for the compiler to find them, or is that just convention?

     • [?] how does it know where on the hard drive to find the header file anyway, since it’s not in the same directory as the .c file?

• hey there’s also decompiling! that’s like what the TOC always tells you not to do!

  • you don’t get back exactly what went in. the code will be a hot mess because things like variable names aren’t preserved, and even for loops and while loops might compile into the same thing. and presumably also comments are lost etc—basically the compiler keeps only the bare minimum necessary to run your code.

debugging

• logical error vs syntax error
• using the VS Code debugger

arrays and strings

• every element of an array has to be the same type

• in C, you can’t “ask the array how big it is”, you the programmer need to know

  • if i heard correctly, it’s impossible to write a function to calculate the length of an array in C! or, it’s impossible to use that kind of function to get a parameter that you pass into something alongside the array itself?
    • the reason you can do it with strings is because of that sentinel character at the end
  • you can use a global variable to track the size of the array, and have a function like average(array) call on that global variable to define its loop etc, but it would be better design if instead you defined your function as average(array, length) and then the loop etc would be in terms of just local variables
  • in other words, to avoid having a function access a global variable, make the function take an extra argument instead, and have the func definition refer to that arg instead of the global

• declare arrays like int scores[3]; where 3 is the length of the array

  • what happens if you try declaring it like int scores[]; and don’t give a length?

• strings are just arrays of chars in c

  • you can directly access the characters by index just with stringname[i]