Linux daemon set /proc/

Question

I once wrote a simple daemon in bash - also sets the values in /proc/*. For example,

echo 50 > /sys/class/backlight/acpi_video0/brightness

I want to rewrite in C + + and share - but how to use the /proc/* in C++? as the client

Answer 1

Remember: on Unix, everything is a file (well, granted, almost everything).

Your current shell code actually means: write the value 50 (echo 50) into the file (redirection operator >) which name follows (/sys/class/backlight/acpi_video0/brightness).

---

In C++, just open /sys/class/backlight/acpi_video0/brightness as a file and read/write to it using whatever method you prefer: C++ fstream, C fopen/fread/fwrite, ...

Example with fstream (namely ofstream since we're only writing to it):

std::ofstream file("/sys/class/backlight/acpi_video0/brightness");
if (!file.is_open())
    throw std::runtime_error("Could not open the file");
file << 50;
file.close();

Answer 2

Code sample:

int val = 50;

FILE *f = fopen("/sys/class/backlight/acpi_video0/brightness", "w");
if (!f)
{
   fprintf(stderr, "Huh, couldn't open /sys/class ... ");
   exit(1);
}
fprintf(f, "%d", val);
fclose(f);