so I asked here few days ago about C# and its principles. Now, if I may, I have some additional general questions about some languages, because for novice like me, it seems a bit confusing. To be exact I want to ask more about language functions capabilities than syntax and so.
To be honest, its just these special functions that bothers me and make me so confused. For example, C has its printf(), Pascal has writeln() and so. I know in basic the output in assembler of these functions would be similar, every language has more or less its special functions. For console output, for file manipulation, etc. But all these functions are de-facto part of its OS API, so why is for example in C distinguished between C standard library functions and (on Windows) WinAPI functions when even printf() has to use some Windows feature, call some of its function to actually show desired text on console window, becouse the actual “showing” is done by OS. Where is the line between language functions and system API?
Now languages I don’t quite understand – Python, Ruby and similar. To be more specific, I know they are similar to java and C# in term they are compiled into bytecode. But, I do not unerstand what are its capabilities in term of building GUI applications. I saw tutorial for using Ruby to program GUI applications on Linux and Windows. But isn´t that just some kind of upgrade? I mean fram other tutorials It seemed like these languages was first intended for small scripts than building big applications.
I hope you understand why I am confused. If you do, please help me sort it out a bit, I have no one to ask.
At the bottom you have the OS kernel itself – code that runs in a special CPU mode that allows direct access to otherwise protected resources. You will never have to deal with this unless you’re an OS developer.
Then comes a do-not-cross line seperating this “kernel space” from “user space”. Everything you do as “normal” developer is done in user space.
The OS kernel exports a limited number of very basic functions into user space, dubbed “system calls”. Open a file, read / write a number of bytes, closing the file, for example.
Because these system calls usually require some Assembler code developers don’t want to be bothered with, they are “wrapped” in (usually) C code functions: open(), read(), write(), close().
Now come two sets of APIs available to the developer: The OS API, and the standard language API.
The standard language API provides functions that can be used on any platform supporting the language: fopen(), fputc(), fgetc(), fclose(). It will also provide higher-level functions that make life easier: fprintf(), for example.
The OS API provides its own set of functions. These are not portable to a different operating system, but might be more intuitive to use, or more powerful, or merely different. OpenFile(), ReadFile(), WriteFile(), CloseFile(). Again, higher-level functions might be available, i.e. PrintLn().
The two sets of functions might partially rely on each other, or make system calls directly, but that shouldn’t bother you too much. You should, however, decide beforehand which set of functions you will want to use for your project, because mixing the two sets – while not a mistake in itself – opens a whole new can of worms (i.e., potential errors).