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Learn C The Hard Way

learncodethehardway.org

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Re: Learn C The Hard Way

#21

Post by eliben »

zedshaw wrote: post #10
ctdonath wrote: post #3

I look forward to the content. As a beginning C++ instructor I find there is something lacking between the truth of the language and the conventions for presenting it. Nobody, AFAIK save for the truly hardcore student, has nailed it.

Got any feedback on the things students get wrong? My experience is they fail to grasp memory management, pointers, functions as pointers, linkers or just how a program actually runs. If you've got others I'd love to hear them.

My experience as an interviewer showed that in addition to the things you listed, people often fail to grasp binary representation of numbers in a computer at all.

This most often comes up when people are asked to do some binary manipulation of numbers, i.e.:

  unsigned u = 19;
  unsigned v = u >> 1;
"v" is now 9, and to really understand it one must grasp how numbers are represented in binary under the hood.

People also fail to understand strings:

  char* s = "string literal";
To some, it's absolutely opaque that the first byte "s" points to contains 0x73, and that represents "s" in ASCII.

Re: Learn C The Hard Way

#22

Post by rpearl »

zedshaw wrote: post #10
ctdonath wrote: post #3

I look forward to the content. As a beginning C++ instructor I find there is something lacking between the truth of the language and the conventions for presenting it. Nobody, AFAIK save for the truly hardcore student, has nailed it.

Got any feedback on the things students get wrong? My experience is they fail to grasp memory management, pointers, functions as pointers, linkers or just how a program actually runs. If you've got others I'd love to hear them.

As a teaching assistant for a class (http://www.cs.cmu.edu/~410/) where students write a whole lot of code in C, please introduce the address-of (&) operator and explain how to obtain pointers without using malloc(). Do this before the concept of the heap is ever introduced at all.

Be careful when explaining the compiler and how a program actually runs. I've found that a lot of student problems come from "the compiler is magic" when it really isn't (maybe related to my other surprised comment below, about how people "don't get C"--they attribute too much magic to the compiler.) Maybe even emphasize that every piece of C code can be translated in a fairly easy fashion to a pretty small amount of assembly.

For the preprocessor, emphasize that it is a solely textual replacement, with no symbolic evaluation. Explain why:

    #define FOO BAR + BAZ
or

    #define MAX(x,y) (((x)
will go horribly wrong (the first in 5*FOO, the second in MAX(x++, y++)).

Re: Learn C The Hard Way

#23

Post by roundsquare »

rpearl wrote: post #5

Do people really think C is some mysterious, inscrutable language? "To many programmers, this makes C scary and evil." Is this actually true for people? I find C code generally very easy and straightforward to understand; there's not any magic behind the scenes, like there is in any language that's more "high level" than C.

It was for a while with me. I was a more "mathy" CS major which meant that languages that exposed what the computer was doing were more opaque to me... but I'm not sure that I ever considered it "scary and evil."

Re: Learn C The Hard Way

#24

Post by signa11 »

zedshaw wrote: post #10
ctdonath wrote: post #3

I look forward to the content. As a beginning C++ instructor I find there is something lacking between the truth of the language and the conventions for presenting it. Nobody, AFAIK save for the truly hardcore student, has nailed it.

Got any feedback on the things students get wrong? My experience is they fail to grasp memory management, pointers, functions as pointers, linkers or just how a program actually runs. If you've got others I'd love to hear them.

imho, please do have a look at "expert c programming" it is quite nice. the conversational style of the book makes it very enjoyable to read.

Re: Learn C The Hard Way

#26

Post by synacksynack »

zedshaw wrote: post #10
ctdonath wrote: post #3

I look forward to the content. As a beginning C++ instructor I find there is something lacking between the truth of the language and the conventions for presenting it. Nobody, AFAIK save for the truly hardcore student, has nailed it.

Got any feedback on the things students get wrong? My experience is they fail to grasp memory management, pointers, functions as pointers, linkers or just how a program actually runs. If you've got others I'd love to hear them.

The arrow operator and identifiers with leading underscores seem to be glossed over or skipped fairly often in education. It's intimidating to look at code that uses them if you don't know what they are.

Re: Learn C The Hard Way

#27

Post by kingkilr »

zedshaw wrote: post #13
getsat wrote: post #8

Why is %d used to interpolate an integer into a format string? I don't recall seeing this done for any reason before. I hope Zed actually covers how dangerous format strings can be if not handled properly. Format strings are still (hilariously) one of the major exploitation vectors in C-based applications today. Edit: According to Wikipedia, %i and %d are synonymous. Sorry for the confusion.

It's not for the type, but for the output. The 'd' means "decimal" output. For example, you can do %x to "hexadecimal" output, and %o for octal. Of course, there's some complex interplay with what type you hand that function. As for how "dangerous" it is, yeah it's not going to rape your family, it'll just crash. So I'll be showing people how to prevent it.

> it's not going to rape your family, it'll just crash

Well, if it hits undefined behavior it could in fact rape your family, the standard allows for that.

Re: Learn C The Hard Way

#28

Post by alderssc »

ramidarigaz wrote: post #11
rpearl wrote: post #5

Do people really think C is some mysterious, inscrutable language? "To many programmers, this makes C scary and evil." Is this actually true for people? I find C code generally very easy and straightforward to understand; there's not any magic behind the scenes, like there is in any language that's more "high level" than C.

Many of the friends I made in my CS classes were terrible with pointers. I never really understood why they didn't grasp pointers, but it was a major stumbling block for them in C/C++

I would hazard to guess its due to two things: 1) a lack of understanding about how the machine works, and in particular the way the memory is organized; and 2) lack of explanation of why anyone would need to use pointers. Introducing pointers in the context of a linked list, or explaining call-by-reference would probably help make things more concrete.

Re: Learn C The Hard Way

#29

Post by getsat »

zedshaw wrote: post #13
getsat wrote: post #8

Why is %d used to interpolate an integer into a format string? I don't recall seeing this done for any reason before. I hope Zed actually covers how dangerous format strings can be if not handled properly. Format strings are still (hilariously) one of the major exploitation vectors in C-based applications today. Edit: According to Wikipedia, %i and %d are synonymous. Sorry for the confusion.

It's not for the type, but for the output. The 'd' means "decimal" output. For example, you can do %x to "hexadecimal" output, and %o for octal. Of course, there's some complex interplay with what type you hand that function. As for how "dangerous" it is, yeah it's not going to rape your family, it'll just crash. So I'll be showing people how to prevent it.

It'll crash and potentially allow code execution if the rest of the args are user coercible. Check out the first few chapters of The Shellcoder's Handbook for examples.

Thanks for the explanation. I've never seen/had to use %d with integers. I've only used it with %.Nd for floats/doubles.

Re: Learn C The Hard Way

#30

Post by briandoll »

I'm very excited to see Zed working on this. This exercise-driven tutorial format seems efficient and practical, but what makes this really stand out is Zed's approach to the overall goal.

I greatly appreciate an 'opinionated' programming book. I've probably heard more debates on formatting and style for C than any other language.

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