Thread: Compiler in C?

Hello I am new to C programming, and I am wondering how to (if it is possible and I really hope it is possible) to have an executable.. when run, write another program... compile it, and run it?

Say for example, there is a program that will make an executable that works based on the user input?
Or even an executable that clones itself when run? (I know it could be used maliciously but those are not my intentions)

Thanks, Jonny

Originally Posted by Jonnyb42

Hello I am new to C programming, and I am wondering how to (if it is possible and I really hope it is possible) to have an executable.. when run, write another program... compile it, and run it?

~Jonny

Sure, you could make an external call to a compiler, check the output, and run the result.

Originally Posted by Jonnyb42

Wow sweet!! Now, how hard is it to write a C compiler in C only? I mean like one which is as simple as possible, doesn't need GUI or special features or whatever, just for a call to compile like you said.

Take a look at tcc (Tiny C Compiler). It's about as small as you'll get, and it's about 10,000 lines.

Oh and the answer is somewhat, "very hard".

thanks guys this is awesome!
Just some extra questions, Why is it so hard to write a compiler, or why does it take so many lines? Also, if anyone knows robotics, but if you had a microntroller, is it possible to have it hook up to another microcontroller and load its instructions on it, without an external programmer?(in the C language of course)

(edited):
Actually, could you tell me how to use TCC, perhaps compile commands in C or how to implement it in code?
I have Vista in case that would change things.

Thanks again,

10000 lines for a compiler is very small (hence the name "tiny c compiler").

A "proper" C compiler is probably 100K-1M+ lines of code. gcc is absolutely enormous, but it also supported more than a dozen different processor families, multiple language variants (e.g. C++, Objective C, standard C) and several dialects/standards (e.g. C std89, C std99, gcc99), many optimization options, etc, etc.

There are two main difficulties in writing a compiler:
1. Parsing the language.
2. Generating meaningful code output.

C is a not a huge language, but there are some rather complex constructions, and there are quite a few different operators.

There are other languages that are easier to implement.

Have a look at the MiniBasic implementation we've (me and a few others on this forum) done here:
matsp / minibasic / overview — bitbucket.org
It is about 3300 lines of C++ code.

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Mats

Originally Posted by Brafil

Can you even write a complete C compiler in C?

Yes.

Originally Posted by Brafil

Ok. I meant "without any other language involved". Such as machine language (not a "real" language, though) as the output. But you're right.

Brafil has a point here. How could you write a compiler that produces executable objects without including a concrete translation into assembly (not to say I don't believe it, just kind of curious about how)?

Originally Posted by Brafil

Can you even write a complete C compiler in C? What about assembly? Most compilers produce assembly code. You'll have to be fluent in this

The compiler generates assembler code (or the binary equivalent thereof), but the code to do the actual compilation is normally written in C. Naturally, the VERY FIRST C compiler was NOT written in C, because there was no C compiler to compile it with.

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Mats

Originally Posted by matsp

The compiler generates assembler code (or the binary equivalent thereof), but the code to do the actual compilation is normally written in C.

But surely, sir, there is a ton of __inline asm__ in there?

Originally Posted by MK27

But surely, sir, there is a ton of __inline asm__ in there?

That would not be necessary at all. Remember, we are talking about what can be done, not what is typically done.