An overview of C and C++

A long this lecture let us test a basic Hello World scripts on C by turning ON or OFF the USR3 LED. The idea is to remember the compilation chain process to obtain an executable application.

The Hello-World on C

The code used for this example is in the file main.c and listed below

// LED application to turn on or off the user LED3
// Sep 2022
// Gerardo Marx

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

//definitions:
#define LED3 "/sys/class/leds/beaglebone:green:usr3"

// Prototype functions

void WriteLED(char path[], char value[]); //Write commands to the LED path
void RemoveTrigger(); //remove the trigger of LED

// main
int main(int argc, char* argv[]){
	if(argc!=2){
		printf("Incorrect number of arguments ....\n");
		printf("use './main on' to turn on the LED\n");
		printf("use './main off' to turn off the LED\n");
		printf("----------------------\n");
		// more information for the user
		return 2;
	}
	printf("Number of Arguments OK\n");
	if(strcmp(argv[1], "on")==0){
		printf("LED on\n");
		RemoveTrigger();
		WriteLED("/brightness", "1");
	}
	else if(strcmp(argv[1], "off")==0){
		printf("LED off\n");	
		RemoveTrigger();
		WriteLED("/brightness", "0");
	}
	printf("App done!!!!\n");
	printf("----------------------\n");
	return 0;
}

// complete functions:
// Write command to a LED path
void WriteLED(char ledpath[], char value[]){
	FILE* fp; //file pointer to LED path
	char fullPath[100]; //variable to store the full LED path
	sprintf(fullPath, LED3 "%s", ledpath); 
    fp = fopen(fullPath, "w+");
	fprintf(fp, "%s", value);
	fclose(fp);
}

void RemoveTrigger(){
	WriteLED("/trigger", "none");
}
 

then, to compile on an executable code use

$ gcc main.c -o main

here the main is the name that you want for your executable code; you can modify it or change it.

Now it is possible to execute your new code by using:

$ ./main on

Your tasks

1. Improve this code to work with any User LED
2. Create a makefile to compile and clean this project
3. Add a new fucntion to determine the LED status(trigger)
4. Improve this Redme file to explain the libraries and functions used