Thread: How to use loadJPG function from library jpeg?

Hi all,

As my name implies, I just started learning how to program in C.
I have a homework assignment that requires me to use the function loadJPG
to decompress an image. I've never encounter this function before, so I have no idea how it works, or even how to call it. My instructor never explain it in class either.

The function has the prototype:
int loadJPG(const char* input_file_name,
const char * output_file_name);

So, I'm suppose to supply it with an input file name and a output file name, something that I'm totally unfamiliar with...

How are we suppose to use a file name as an argument and expect it to give us another file of some sort?

It'd be great if anyone can explain that function to me, and more importantly, teach me how to use it.

Thanks!!!

Presumably you know what filenames are. For now you can think of "const char *" as "things in quotes" if you want (but it could also be a char array).

Code:

loadJPG("file1", "file2");

What library is that in?

Frankly if you haven't been taught about strings and filenames yet... this assignment would be way too advanced for your class.

@tabstop
If filename means anything other than the name of a file, then I don't know what it is...
The idea of using the name of a file, something that's not declared inside a program, is totally foreign to me.
But then again, if filename refers to something in a program, then it's a different story (A story that I've not yet been told).

@CommonTater
We've been taught about strings.
My instructor does have a tendency to give assignments that are almost impossible to do, especially for a class that supposedly requires no previous programming experience.

If you know what a filename is, and you've been taught about strings, then you're done.

Let's say I want to compress a file named low.jpeg, and save the output into a file named high, do I just call the function like this:
loadJPG("low.jpeg, "high");
?

The files are on my school's server (running on linux). According to the instruction, the output file is a "binary file". Since there are information I need to get from the output file, I thinkI should make it a text file so I can read it.

Thank you for your help AndrewHunter!

The function is provided in the assignment; the function prototype is:

Code:

int loadJPG(const char* input_file_name,
const char * output_file_name);

The assignment itself is quite long with almost 3 pages of instructions. Essentially, we have to decompress an image file toobtain it's pixel data and read them into memory then compute the color histogram for the image.

I really don't know anything about the function since it's not included in the book, or mentioned in the class.

But you have three pages of instructions, and I would be willing to bet $x for most any x that all the information you need is in the instructions, if only you were to read them.

Originally Posted by tabstop

But you have three pages of instructions, and I would be willing to bet $x for most any x that all the information you need is in the instructions, if only you were to read them.

I don't know what made you think that I didn't read the instructions. Like I said in the beginning, I'm new to C programming and my instructor really do give long and hard HW problems.
I'm not asking anyone here to write the program for me, only asking the particulars that I don't understand.

Originally Posted by quzah

Your provided library should be telling you what each function does. The function prototype sure doesn't tell us anything useful:

Name: loadJPG - Ok, this seems to say it's going to open a file for us and put its contents someplace.
Returns: An int. Well that's unhelpful. It's obviously not putting it there. Must be an error value then for if it fails or nto.
arg1: input_file_name - Ok, that's at least obvious.
arg2: output_file_name - What? Why are we outputting anything? I thought we were loading a file? Why do I need an output file name?

This function prototype tells us nothing of what this function does, so you'd better go hit up your teacher for what this actually does. Or as tabstop said, actually read your instructions.


Quzah.

Again, I don't know why people here think I'm not reading the instructions. If they were crystal clear, I wouldn't be here posting questions.
I thought the function I'm using is somewhat prevalent, so there's a chance that someone here is familiar with it. That's obviously not the case