Question

I am implementing an SMTP-sender in C which is supposed to read a file from a directory whenever it is created, process data and delete the file.

How can I implement this polling function which should keep doing this automatically?

Answer 1

A simple option is to run your program periodically from cron. The program can use the Linux API call readdir to iterate through a directory. It doesn’t have to actively monitor the directory.

Here’s a simple code example:

#include <stdio.h>
#include <sys/types.h>
#include <dirent.h>
int main()
{
   DIR* dp = opendir(".");
   struct dirent* de;
   while (de = readdir(dp))
   { 
     if (de->d_type != DT_REG) // Only print regular files
        continue;
      printf("Found file %s\n", de->d_name);
   }
   closedir(dp);
}

Disclaimer: For the sake of simplicity I did not include code to check or handle error conditons.