C++ – How to hook up LED lights in C++ without microcontroller

c++led

I want to light up/off LEDs without a microcontroller. I'm looking to control the LEDs by writing a C++ program. but the problem im having is hooking them up is there a free way to do !!!!

I'm using Windows XP if that is relevant.

I have LEDs but I don't have a microcontroller.

Well, I found some functions but their headers are not working, so can someone help me find headers?

Here is an example of what I'm talking about:

poke(0x0000,0x0417,16);
gotoxy(1,1);
printf("Num Lock LED is now on    r");
delay(10);

Also, does anyone have a "Kernel Programming" eBook?

I also need a circuit diagram to show where to hook up the LEDs.

Best Solution

That completely depends on which hardware you have, which determines which driver you need. Back then, i got a simple led and put it into the printer LPT port. Then i could write a byte to address 0x0378h and the bits in it determined whether a pin had power or not (using linux). For windows, you need a driver that allows you to access the lpt port directly. I did it with a friend back then too, and it worked nicely (we built up a traffic light :)) Read this page (click on Parallel Port on the left. For some reason, i cannot link directly to it) for details on windows. And read man outb on linux. Now, that Port is really old. But if you have some machine around that still got one, i think it's a lot of fun to play with it.

Anyway, i've got a fritz box that has a neat LED. One can connect to it via telnet and then write something (i forgot the numbers) into /proc/led iirc. A kernel driver then interprets the number and makes the right LED blink. That's another way of doing it :)

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

C++ – How to iterate over the words of a string

I use this to split string by a delimiter. The first puts the results in a pre-constructed vector, the second returns a new vector.

#include <string>
#include <sstream>
#include <vector>
#include <iterator>

template <typename Out>
void split(const std::string &s, char delim, Out result) {
    std::istringstream iss(s);
    std::string item;
    while (std::getline(iss, item, delim)) {
        *result++ = item;
    }
}

std::vector<std::string> split(const std::string &s, char delim) {
    std::vector<std::string> elems;
    split(s, delim, std::back_inserter(elems));
    return elems;
}

Note that this solution does not skip empty tokens, so the following will find 4 items, one of which is empty:

std::vector<std::string> x = split("one:two::three", ':');