Write to Linux sysfs node in C

Question

From the shell I can activate the leds on my system like this:

#echo 1 > /sys/class/leds/NAME:COLOR:LOCATION/brightness

I want to do the exact same thing from a C program, but I have not been able to find a simple example on how to accomplish this?

Answer 1

Open the sysfs node like a file, write '1' to it, and close it again.

For example:

#include <stdio.h>
#include <fcntl.h>

void enable_led() {
  int fd;
  char d = '1';
  fd = open("sys/class/leds/NAME:COLOR:LOCATION/brightness", O_WRONLY);
  write (fd, &d, 1);
  close(fd);
}

Answer 2

Something like this:

#include <stdio.h>

int main(int argc, char **argv)
{
    FILE* f = fopen("/sys/class/leds/NAME:COLOR:LOCATION/brightness", "w");
    if (f == NULL) {
        fprintf(stderr, "Unable to open path for writing\n");
        return 1;
    }

    fprintf(f, "1\n");
    fclose(f);
    return 0;
}

Answer 3

I'm not booted into my linux partition, but I suspect it goes something like this:

int f = open("/sys/class/leds/NAME:COLOR:LOCATION/brightness",O_WRONLY);
if (f != -1)
{
    write(f, "1", 1);
    close(f);
}