Script started on Wed Oct 30 12:31:09 2024
mweeks@air:C_ch16$ echo code is 4392
code is 4392
mweeks@air:C_ch16$ cat C_ch16_11.c
/*
  See Kim King's book, page 403.
  This is an expanded example with code added by Michael Weeks.
*/
#include <stdio.h>

enum {CLUBS, DIAMONDS, HEARTS, SPADES} s;

void print_suit(int s1) {
  switch (s1) {
    case CLUBS:
      printf("Clubs");
      break;
    case DIAMONDS:
      printf("Diamonds");
      break;
    case HEARTS:
      printf("Hearts");
      break;
    case SPADES:
      printf("Spades");
      break;
    default:
      printf("Unknown");
  }
}

int main() {
  int i;

  i = DIAMONDS;   /* i is now 1               */
  printf("i = %d, which is ", i);
  print_suit(i);  
  printf("\n");

  s = 0;          /* s is now 0 (CLUBS)       */
  printf("s = %d, which is ", s);
  print_suit(s);  
  printf("\n");

  s++;            /* s is now 1 (DIAMONDS)    */
  printf("s = %d, which is ", s);
  print_suit(s);  
  printf("\n");

  i = s + 2;      /* i is now 3               */
  printf("i = %d, which is ", i);
  print_suit(i);  
  printf("\n");

  return 0;
}
mweeks@air:C_ch16$ gcc C_ch16_11.c
mweeks@air:C_ch16$ ./a.out
i = 1, which is Diamonds
s = 0, which is Clubs
s = 1, which is Diamonds
i = 3, which is Spades
mweeks@air:C_ch16$ cd ../C_Ch17
mweeks@air:C_Ch17$ cat C_ch17_1.c
  p = malloc(10000);

  if (p == NULL) {
  /* allocation failed; take appropriate action */
  }

  if ((p = malloc(10000)) == NULL) {
  /* allocation failed; take appropriate action  */
  }

mweeks@air:C_Ch17$ echo malloc = memory allocate
malloc = memory allocate
mweeks@air:C_Ch17$ cat C_ch17_2.c
    void *malloc(size_t size);

"size_t" is an unsigned integer type defined in the library.
mweeks@air:C_Ch17$ cat C_ch17_3.c
"malloc" to allocate memory for a string of "n" characters:

    p = malloc(n + 1);


cast "malloc" return value (not required):
    p = (char *) malloc(n + 1);

mweeks@air:C_Ch17$ cat C_ch17_4.c
#include <stdio.h>
#include <stdlib.h>

struct rec { 
      char LastName[41]; 
      char FirstName[41]; 
    }; 

    struct rec *r; 

    r = (struct rec *) malloc(sizeof(struct rec)); 

mweeks@air:C_Ch17$ cat malloc_ex1.c 
#include <stdio.h>
#include <stdlib.h>

int main() {
  char *p;

  p = malloc(10000);
  if (p == NULL) {
    printf("Could not allocate memory\n");
    exit(0);
  }

  printf("Memory allocation worked\n");
  free(p);

  return 0;
}
mweeks@air:C_Ch17$ gcc malloc_ex1.c
mweeks@air:C_Ch17$ ./a.out
Memory allocation worked
mweeks@air:C_Ch17$ gcc malloc_ex2.c
malloc_ex2.c:9:5: error: array type 'char [10000]' is not assignable
  p = malloc(10000);
  ~ ^
malloc_ex2.c:12:12: warning: comparison between pointer and integer
      ('int' and 'void *')
  if (p[0] == NULL) {
      ~~~~ ^  ~~~~
1 warning and 1 error generated.
mweeks@air:C_Ch17$ cat malloc_ex2.c
#include <stdio.h>
#include <stdlib.h>

int main() {

  //char p[] = malloc(10000);
  char p[10000];

  p = malloc(10000);

  // this does not really work
  if (p[0] == NULL) {
    printf("Could not allocate memory\n");
    exit(0);
  }

  printf("Memory allocation worked\n");
  free(p);

  return 0;
}
mweeks@air:C_Ch17$ cat malloc_ex2b.c
#include <stdio.h>
#include <stdlib.h>

int main() {

  //char p[] = malloc(10000);
  char *p;

  p = malloc(10000);

  if (p == NULL) {
    printf("Could not allocate memory\n");
    exit(0);
  }

  printf("Memory allocation worked\n");
  printf("p[123] is %d\n", p[123]);

  free(p);

  return 0;
}
mweeks@air:C_Ch17$ gcc malloc_ex2b.c
mweeks@air:C_Ch17$ ./a.out
Memory allocation worked
p[123] is 0
mweeks@air:C_Ch17$ cat cat C_ch17_5.c 
cat: cat: No such file or directory
p = malloc( ... );
q = malloc( ... );
p = q;

// nothing points to p's original memory!
// called "garbage"

// No garbage collector in C

// use "free" instead
mweeks@air:C_Ch17$ cat cat C_ch17_6.c 
cat: cat: No such file or directory
    char *p = malloc(4);
    ...

    free(p);
    ...

    strcpy (p, "abc"); // WRONG

mweeks@air:C_Ch17$ cat C_ch17_6.c 
    char *p = malloc(4);
    ...

    free(p);
    ...

    strcpy (p, "abc"); // WRONG

mweeks@air:C_Ch17$ grep fope *.c
C_ch17_7.c:  fp = fopen("test.txt", "r");
mweeks@air:C_Ch17$ vi C_ch17_8.c
mweeks@air:C_Ch17$ vi C_ch17_9.c
mweeks@air:C_Ch17$ vi C_ch17_10.c

[No write since last change]

Press ENTER or type command to continue
mweeks@air:C_Ch17$ cat C_ch17_10.c 

#include <stdio.h>

int main() { 

//  char *p = malloc(1024);
//  if (p == NULL) {
     printf("Could not allocate memory/n");
//     exit(2);
//  }

//  fp = fopen("test.txt", "r");


//  free(p);
  return 0;
}
mweeks@air:C_Ch17$ gcc C_ch17_10.c 
mweeks@air:C_Ch17$ ./a.out
Could not allocate memory/nmweeks@air:C_Ch17$ 
mweeks@air:C_Ch17$ 
mweeks@air:C_Ch17$ vi C_ch17_10.c
mweeks@air:C_Ch17$ gcc C_ch17_10.c 
mweeks@air:C_Ch17$ ./a.out
Could not allocate memory
mweeks@air:C_Ch17$ vi C_ch17_10.c
mweeks@air:C_Ch17$ cat C_ch17_10.c

#include <stdio.h>

int main() { 

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    exit(1);
  }
  // .. do some file stuff

  // Close the stream
  fclose(fp);

  free(p);

  return 0;
}
mweeks@air:C_Ch17$ cp C_ch17_10.c C_ch17_10_v2.c
mweeks@air:C_Ch17$ vi C_ch17_10_v2.c 
mweeks@air:C_Ch17$ cat C_ch17_10_v2.c

#include <stdio.h>

int main() { 

  char *p = malloc(1024);
  if (p == NULL) {
     printf("Could not allocate memory\n");
     exit(2);
  }

  fp = fopen("test.txt", "r");
  // Always check to see if the command worked.
  if (fp == NULL) {
    // It did not work, so quit.
    printf("Error: fopen command failed\n");
    free(p); // Free up the memory before exiting
    exit(1);
  }
  // .. do some file stuff

  // Close the stream
  fclose(fp);

  free(p);

  return 0;
}
mweeks@air:C_Ch17$ cat C_ch17_7.c
#include <stdio.h>

int main() {
  FILE *fp;

  fp = fopen("test.txt", "r");

  char buff[255]; // n=255
  // read 
  fgets(buff, 255 , (FILE*)fp);
  printf("%s\n", buff );

  // write
  // fputs("test.txt", fp);

  fclose(fp);

  return 0;
}
mweeks@air:C_Ch17$ cat C_ch17_8.c
#include <stdio.h> 

int main( int argc, char *argv[] ) { 
  printf("Program name %s\n", argv[0]); 
  if ( argc == 2 ) { 
    printf("The argument supplied is %s\n", argv[1]); 
  } 
  else if ( argc > 2 ) { 
    printf("Too many arguments supplied.\n"); 
  } 
  return 0;
} 
mweeks@air:C_Ch17$ gcc C_ch17_8.c
mweeks@air:C_Ch17$ ./a.out
Program name ./a.out
mweeks@air:C_Ch17$ ./a.out onething
Program name ./a.out
The argument supplied is onething
mweeks@air:C_Ch17$ ./a.out onething twothings
Program name ./a.out
Too many arguments supplied.
mweeks@air:C_Ch17$ cat C_ch17_9.c
    int count[26]={0};
    ...
    c=buff[i];
    if (c>='a' && c<='z')
        count[c-'a']++;
    else if (c >='A' && c <='Z')
        count[c- 'A']++;
    ...

mweeks@air:C_Ch17$ exit
exit

Script done on Wed Oct 30 13:45:12 2024