Code samples from Computer Networks I Lab Manual, Chapter 3 - Program I/O with the Getopt and Syslog Libraries

fig3-1.c

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

#define NAME_LENGTH 20

int main()
{
  char name[NAME_LENGTH];

  printf("Please enter your name: ");

  if (fgets(name, NAME_LENGTH, stdin) != NULL)
  {
    printf("Nice to meet you, %s", name);
  }

  exit(EXIT_SUCCESS);
}

fig3-10.c

#include <syslog.h>
#include <stdlib.h>

int main()
{
  int i = 42;
  char* str = "universe";

  openlog("fig3-10", LOG_PERROR | LOG_PID | LOG_NDELAY, LOG_USER);
  syslog(LOG_INFO, "The answer to the %s is %d", str, i);
  closelog();

  exit(EXIT_SUCCESS);
}

fig3-11.c

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

int main(int argc, char** argv)
{
  FILE* file;

  openlog("fig3-11", LOG_PERROR | LOG_PID | LOG_NDELAY, LOG_USER);

  syslog(LOG_DEBUG, "Program started");
  syslog(LOG_DEBUG, "Testing arguments");
  syslog(LOG_DEBUG, "Arguments passed to the program: %d", argc);

  // Check if a filename was passed as an argument
  if (argc != 2)
  {
    syslog(LOG_ERR, "No filename specified");
    closelog();
    exit(EXIT_FAILURE);
  }

  // If so, open the file
  syslog(LOG_DEBUG, "Opening file '%s'", argv[1]);
  file = fopen(argv[1], "r");

  // Ensure the file was opened successfully
  if (file == NULL)
  {
    syslog(LOG_ERR, "The specified file could not be opened");
    closelog();
    exit(EXIT_FAILURE);
  }

  syslog(LOG_INFO, "The file '%s' exists and was successfully opened!", argv[1]);
  close(file);
  closelog();
  exit(EXIT_SUCCESS);
}

fig3-12.c

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

int main(int argc, char** argv)
{
  FILE* file;

  setlogmask(LOG_UPTO(LOG_INFO));

  openlog("fig3-12", LOG_PERROR | LOG_PID | LOG_NDELAY, LOG_USER);

  syslog(LOG_DEBUG, "Program started");
  syslog(LOG_DEBUG, "Testing arguments");
  syslog(LOG_DEBUG, "Arguments passed to the program: %d", argc);

  if (argc != 2)
  {
    syslog(LOG_ERR, "No filename specified");
    closelog();
    exit(EXIT_FAILURE);
  }

  syslog(LOG_DEBUG, "Opening file '%s'", argv[1]);
  file = fopen(argv[1], "r");

  if (file == NULL)
  {
    syslog(LOG_ERR, "The specified file could not be opened");
    closelog();
    exit(EXIT_FAILURE);
  }

  syslog(LOG_INFO, "The file '%s' exists and was successfully opened!", argv[1]);
  close(file);
  closelog();
  exit(EXIT_SUCCESS);
}

fig3-2.c

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

int main(int argc, char** argv)
{
  bool verbose = false;
  char* log_filename;
  int i;

  // Iterate over the command line arguments
  for (i = 1; i < argc; ++i)
  {
    // Check for the --verbose / -v flag
    if (strcmp(argv[i], "--verbose") == 0 || strcmp(argv[i], "-v") == 0)
    {
      verbose = true;
    }

    // Check for the --log / -l flag
    else if (strcmp(argv[i], "--log") == 0 || strcmp(argv[i], "-l") == 0)
    {
      // Ensure that an argument was provided
      if (i + 1 == argc) {
        fprintf(stderr, "The --log / -l option requires an argument\n");
        exit(EXIT_FAILURE);
      }
      else {
        log_filename = argv[++i];
      }
    }
  }

  printf("Verbose : %s\n", verbose ? "true" : "false");
  printf("Log     : %s\n", log_filename);

  exit(EXIT_SUCCESS);
}

fig3-3.c

#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <stdbool.h>

int main(int argc, char** argv)
{
  int c;
  bool verbose = false;
  char* log_filename = NULL;

  while ((c = getopt(argc, argv, "vl:")) != -1)
  {
    switch(c)
    {
      case 'v':
        verbose = true;
        break; 

      case 'l':
        printf("-l called -- ignoring for now\n");
        break;

      case '?':
        // Error message already printed by getopt -- we'll just exit 
        exit(EXIT_FAILURE);
        break;
    }
  }

  printf("Verbose : %s\n", verbose ? "true" : "false");
  printf("Log     : %s\n", log_filename);

  exit(EXIT_SUCCESS);
}

fig3-4.c

#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <stdbool.h>

int main(int argc, char** argv)
{
  int c;
  bool verbose = false;
  char* log_filename = NULL;

  while ((c = getopt(argc, argv, "vl:")) != -1)
  {
    switch(c)
    {
      case 'v':
        verbose = true;
        break; 

      case 'l':
        log_filename = optarg;
        break;

      case '?':
        // Error message already printed by getopt -- we'll just exit 
        exit(EXIT_FAILURE);
        break;
    }
  }

  printf("Verbose : %s\n", verbose ? "true" : "false");
  printf("Log     : %s\n", log_filename);

  exit(EXIT_SUCCESS);
}

fig3-5.c

#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <stdbool.h>

int main(int argc, char** argv)
{
  int c, i;
  bool verbose = false;
  char* log_filename = NULL;

  while ((c = getopt(argc, argv, "vl:")) != -1)
  {
    switch(c)
    {
      case 'v':
        verbose = true;
        break; 

      case 'l':
        log_filename = optarg;
        break;

      case '?':
        // Error message already printed by getopt -- we'll just exit 
        exit(EXIT_FAILURE);
        break;
    }
  }

  printf("Verbose : %s\n", verbose ? "true" : "false");
  printf("Log : %s\n", log_filename);

  for (i = optind; i < argc; ++i)
  {
    printf("Processing file %s\n", argv[i]);
  }

  exit(EXIT_SUCCESS);
}

fig3-6.c

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

int main(int argc, char** argv)
{
  int c, i;
  static int verbose_flag = 0;
  char* log_filename = NULL;

  while (1)
  {
    static struct option long_options[] = 
    {
      {"verbose",  no_argument,       &verbose_flag,  1 },
      {"log",      required_argument, 0,             'l'},
      {0, 0, 0, 0}
    };

    int option_index = 0;

    c = getopt_long(argc, argv, "vl:", long_options, &option_index);

    // If we've reached the end of the options, stop iterating
    if (c == -1)
      break;

    switch (c)
    {
      case 'l':
        log_filename = optarg;
        break;

      case 'v':
        verbose_flag = 1;
        break;

      case '?':
        // Error message already printed by getopt_long -- we'll just exit 
        exit(EXIT_FAILURE);
        break;
    }
  }

  printf("Verbose : %s\n", verbose_flag ? "true" : "false");
  printf("Log     : %s\n", log_filename);

  for (i = optind; i < argc; ++i)
  {
    printf("Processing file %s\n", argv[i]);
  }

  exit(EXIT_SUCCESS);
}

fig3-7.c

#include <syslog.h>
#include <stdlib.h>

int main()
{
  openlog("fig3-7", LOG_PID | LOG_NDELAY, LOG_USER);

  syslog(LOG_NOTICE, "Hello Syslog!");
  syslog(LOG_INFO, "Here's an informational message.");
  syslog(LOG_WARNING, "Here's a warning.");
  syslog(LOG_ERR, "Here's an error.");
  syslog(LOG_DEBUG, "Here's some debugging information.\n");
  
  closelog();

  exit(EXIT_SUCCESS);
}

fig3-8.c

#include <syslog.h>
#include <stdlib.h>

int main()
{
  openlog("fig3-8", LOG_PERROR | LOG_PID | LOG_NDELAY, LOG_USER);

  syslog(LOG_NOTICE, "Hello Syslog!");
  syslog(LOG_INFO, "Here's an informational message.");
  syslog(LOG_WARNING, "Here's a warning.");
  syslog(LOG_ERR, "Here's an error.");
  syslog(LOG_DEBUG, "Here's some debugging information.\n");
  
  closelog();

  exit(EXIT_SUCCESS);
}

fig3-9.c

#include <syslog.h>
#include <stdlib.h>

void b()
{
  syslog(LOG_DEBUG, "Entering b()");
  syslog(LOG_DEBUG, "Leaving b()");
}

void a()
{
  syslog(LOG_DEBUG, "Entering a()");
  b();
  syslog(LOG_DEBUG, "Leaving a()");
}

int main()
{
  openlog("fig3-9", LOG_PERROR | LOG_PID | LOG_NDELAY, LOG_USER);
  a();
  closelog();

  exit(EXIT_SUCCESS);
}