C Q&A Thread

[sammyMaX]

Awww... whatever, it's not crucial to my program anyways.

[sammyMaX]

Here's another question I have:
To handle input in my program, I have made a

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1	char input[500];

This means the input can only be 500 characters, but if I use fancier dynamic allocation methods this problem still remains: sometimes when I type, weird characters will be outputted in front of the useful text, only to be overwritten as I type more. I might type in "12345", and then have it suddenly turn into "12345[=$_L?<". As I type in more characters, they get overwritten into "123459843406", but more random symbols may pop up later. I really don't know what would be causing that to happen, because my string drawing function has already worked on other things, and I can't find anything wrong with the key detection code. Any ideas?

[ExtendeD]

We would need the code snippet which fills up "input[] to be able to help you, the problem may be there.

[calc84maniac]

Could it be a problem with null-termination? You can't assume that a dynamically allocated buffer (or a fixed-size local buffer) will be filled with 0.

[Tribal]

Yeah, it kinda sounds like a problem with null termination.  You should never assume allocated memory is clean, the safest bet would be to do a

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1 2	memset(input, 0, bytes allocated);

after allocation and see if it still does it.

[ExtendeD]

Or use calloc().

[sammyMaX]

Yay, it works! Thanks again!

[Tribal]

Or use calloc().

I've never used calloc ever since I came across the post on cprogramming's discussion board:

malloc will return an uninitialized chunk of memory for you to use.
calloc ( clear alloc ) will attempt to initialize that chunk of memory to all bits zero.

Note that when I say attempt, I mean that this may not be possible so you shouldn't rely on it. Other than that the only difference is how they are called and how they are implemented. So in the end, which one you choose to use is a matter of preference.

ref: http://cboard.cprogramming.com/c-programming/20505-malloc-vs-calloc.html#post132635

[sammyMaX]

I'm getting a weird problem creating arrays now. Here's the code:

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int numInts1 = ceil(operationPos, 4); int numInts2 = ceil((inputLen - operationPos - 1), 4); int *in1 = (int*)calloc(numInts1, sizeof(int)); int *in2 = (int*)calloc(numInts2, sizeof(int));

Using the Eclipse debugger, numInts1 is what it's supposed to be, and same as numInts2, but the arrays in1 and in2 are always only one int long. Attached a screenshot of the debugger. (What it's showing means that the arrays are one int long, right? Otherwise I wouldn't know what's wrong with my program)

[sammyMaX]

Never mind - got it all fixed. It turns out that Eclipse can't figure out what's an array and what's not when they are dynamically allocated. Just click on the variable and then "Display as an Array."

[Scipi]

How do you use the show_msgbox function?

I have the following code:

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#include <os.h> int main() {     void show_msgbox("Hello World", "Hello Omnimaga");     return 0; }

And it's not compiling with the error:

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Tom@AdmirableCoffee /c/Users/Tom/Desktop/Programs/Ndless/Hello_World $ make nspire-gcc -Os -nostdlib -Wall -W -marm -c main.c main.c: In function 'main': main.c:5:10: error: expected declaration specifiers or '...' before string const ant main.c:5:10: error: expected declaration specifiers or '...' before string const ant main.c:5:10: error: expected declaration specifiers or '...' before numeric cons tant make: *** [main.o] Error 1 Tom@AdmirableCoffee /c/Users/Tom/Desktop/Programs/Ndless/Hello_World $

[Runer112]

Lose the "void" since you're calling the function, not declaring it. As far as making sure you're calling the function with the proper arguments, I can't help you there because I don't know anything about device-specific C development.

[Scipi]

It works. Thanks

I honestly feel I should hit myself over the head hard for something so obvious