Script started on Mon Oct 21 12:59:51 2024
mweeks@air:C_ch13$ cd ../more_programs/
mweeks@air:more_programs$ cat commandline2.c 
/*
   Simple example of a C program
   
   -Michael Weeks

*/

#include "stdio.h"
#include "stdlib.h"
#include "string.h"

#define MAXCHARS 100
#define MAXSTRING 10

int main (int argc, char *argv[]) {

  // An array of MAXSTRING strings
  // Each string can have up to MAXCHARS characters.
  char arg_copy[MAXSTRING][MAXCHARS];

  int i;

  // Copy the arguments as strings to arg_copy
  // This has 2 major problems:
  // 1. What if a string is > MAXCHARS in length?
  // 2. What if there are more than 10 arguments?
  for (i=0; i<argc; i++)
    strcpy(arg_copy[i], argv[i]);

  printf("Command line arguments are:\n");
  for (i=0; i<argc; i++)
    printf("\"%s\" \n", arg_copy[i]);
  printf("\n"); 

  return 0;
}

mweeks@air:more_programs$ gcc commandline2.c
mweeks@air:more_programs$ ./a.out
Command line arguments are:
"./a.out" 

mweeks@air:more_programs$ ./a.out one two three
Command line arguments are:
"./a.out" 
"one" 
"two" 
"three" 

mweeks@air:more_programs$ ./a.out -l -a 
Command line arguments are:
"./a.out" 
"-l" 
"-a" 

mweeks@air:more_programs$ cat double_ptr.c 
/*
Example from
https://stackoverflow.com/questions/897366/how-do-pointer-to-pointers-work-in-c-and-when-might-you-use-them
Sep 1, 2016 at 11:02
msc

(This code was written by user msc)

*/
#include <stdio.h>

int main ()
{
   int  num = 10;
   int  *ptr1;
   int  **ptr2;

   // Take the address of var 
   ptr1 = &num;

   // Take the address of ptr1 using address of operator &
   ptr2 = &ptr1;

   // Print the value
   printf("Value of num = %d\n", num );
   printf("Value available at *ptr1 = %d\n", *ptr1 );
   printf("Value available at **ptr2 = %d\n", **ptr2);
}

mweeks@air:more_programs$ gcc double_ptr.c
mweeks@air:more_programs$ ./a.out
Value of num = 10
Value available at *ptr1 = 10
Value available at **ptr2 = 10
mweeks@air:more_programs$ 
mweeks@air:more_programs$ 
mweeks@air:more_programs$ echo 117
117
mweeks@air:more_programs$ cd ../C_ch13
mweeks@air:C_ch13$ cat test_string1.c 
#include <stdio.h>

    int main() {

      char *str = "Hello World";
      // char str[] = "Hello World";
     
      printf("About to change the H in Hello to h.\n");
      str[0] = 'h';
      printf("%s\n", str); 

      return 0;
    }mweeks@air:C_ch13$ echo non-standard behavior
non-standard behavior
mweeks@air:C_ch13$ gcc test_string1.c
mweeks@air:C_ch13$ ./a.out
About to change the H in Hello to h.
Bus error: 10
mweeks@air:C_ch13$ cat test_string2.c 
#include <stdio.h>

    int main() {

      // char *str = "Hello World";
      char str[] = "Hello World";
     
      printf("About to change the H in Hello to h.\n");
      str[0] = 'h';
      printf("%s\n", str); 

      return 0;
    }mweeks@air:C_ch13$ 
mweeks@air:C_ch13$ gcc test_string2.c 
mweeks@air:C_ch13$ ./a.ot
bash: ./a.ot: No such file or directory
mweeks@air:C_ch13$ ./a.out
About to change the H in Hello to h.
hello World
mweeks@air:C_ch13$ cat ch13_3.c
#include <stdio.h>

int main(){
    char date1[8] = "June 14"; 
        char date1[] = "June 14"; // Length could be omitted 
        char date1[8] = {'J', 'u', 'n', 'e', ' ', '1', '4', '\0'}; 
         char *str = "June 14"; 
         char date2[9] = "June 14";

}
mweeks@air:C_ch13$ 
mweeks@air:C_ch13$ cat string_example.c
#include <stdio.h>
#include <string.h>

int main(){
    char date1[] = {'J', 'u', 'n', 'e', ' ', '1', '4', '\0'}; 
    char date2[] = "October 18"; 

    // strcpy -> strncpy
    // strlen -> strnlen
    // strcat -> strncat

    // strcpy
    //strcpy(date1, date2);
    strncpy(date1, date2, 7);

    printf("%s \n", date1);
    printf("%s \n", date2);

   return 0;
}
mweeks@air:C_ch13$ gcc string_example.c
mweeks@air:C_ch13$ ./a.out
October 
October 18 
mweeks@air:C_ch13$ cat string_example2.c
#include <stdio.h>
#include <string.h>

int main(){
    char date1[] = {'J', 'u', 'n', 'e', ' ', '1', '4', '\0'}; 
    char date2[] = "October 18"; 

    // strcpy -> strncpy
    // strlen -> strnlen
    // strcat -> strncat

    // strcpy
    //strcpy(date1, date2);
    int c = strncmp(date1, date2, 7);

    printf("%s \n", date1);
    printf("%s \n", date2);
    printf("cmp returns %d \n", c);

    c = strncmp(date1, date1, 7);
    printf("cmp returns %d \n", c);

   return 0;
}
mweeks@air:C_ch13$ gcc string_example2.c
mweeks@air:C_ch13$ ./a.out
June 14 
October 18 
cmp returns -5 
cmp returns 0 
mweeks@air:C_ch13$ echo remember to check strncmp's result to 0
> '
remember to check strncmps result to 0

mweeks@air:C_ch13$ diff string_example1.c string_example2.c
diff: string_example1.c: No such file or directory
mweeks@air:C_ch13$ diff string_example.c string_example2.c
14c14
<     strncpy(date1, date2, 7);
---
>     int c = strncmp(date1, date2, 7);
17a18,21
>     printf("cmp returns %d \n", c);
> 
>     c = strncmp(date1, date1, 7);
>     printf("cmp returns %d \n", c);
mweeks@air:C_ch13$ echo $?
1
mweeks@air:C_ch13$ echo "last command had status $?"
last command had status 0
mweeks@air:C_ch13$ cd /usr/bin
mweeks@air:bin$ du
694336	.
mweeks@air:bin$ exit
exit

Script done on Mon Oct 21 13:45:35 2024