mem.c

/*
 * show the difference between the str* functions and the mem* functions
 *
 * Matt Bishop, ECS 36A
 * -- ???		original program
 * -- May 22, 2024	commented and cleaned up
 */
#include <stdio.h>
#include <string.h>
#include <ctype.h>

/*
 * macros
 */
/* next four are strings used to demo str*, mem* */
#define X	"xxxx"
#define Y	"yyyy"
#define BIN	"Ab\0C"
#define NUM	"12341234"
			/* used to demo strtok */
#define LINE 	"0,sensed,81,2017-11-14 08:48:05.000,68.0,142,61"

/*
 * weird print function
 * first argument is printed normally
 * for the second, this prints the first ct chars of x are printed
 * so you can see them all
 */
void printit(char *lead, char x[], int ct)
{
	int i;		/* counter in a for loop */

	/* print the leading part  */
	/* this is a normal string */
	if (lead != NULL)
		printf("%s ", lead);

	/* delimit the string to be printed character by character */
	putchar('\"');

	/* print the chars in the string, either in */
	/* their normal form, or as an octal escape */
	for (i = 0; i < ct; i++){
		if (isprint(x[i]))
			putchar(x[i]);
		else
			printf("\\%03o", x[i]);
	}
	
	/* indicate the end */
	putchar('\"');
}

/*
 * the big cheese
 */
int main(void)
{
	char x[100];		/* buffer for the mem* functions */
	char y[100];		/* buffer for the str* functions */
	char *z1, *z2;		/* char pointer for results of functions */
	int i;			/* counter in a for loop */

	/*
	 * the setup; report what was done
	 */
	(void) strcpy(x, X);
	(void) strcpy(y, Y);
	printit("Initially, x =", x, strlen(x));
	printit(" and y =", y, strlen(y));
	printit(" and BIN =", BIN, 4);
	putchar('\n');
	printf("--------------\n\n");

	/*
	 * now we do a memcpy of BIN onto x
	 */
	(void) memcpy(x, BIN, 4);
	printit("After memcopy of BIN, x =", x, 4);
	putchar('\n');
	/* and a strcpy onto y */
	(void) strcpy(y, BIN);
	printit("After strcpy of BIN, y =", y, 4);
	putchar('\n');
	printf("--------------\n\n");

	/*
	 * now we reset things
	 */
	(void) strcpy(x, X);
	(void) strcpy(y, Y);
	printit("Resetting, x =", x, strlen(x));
	printit(" and y =", y, strlen(y));
	printit(" and BIN =", BIN, 4);
	putchar('\n');
	printf("--------------\n\n");

	/*
	 * now we do a comparison
	 */
	(void) strcpy(y, BIN);
	printit("After strcpy of BIN, y =", y, 4);
	putchar('\n');
	printf("strcmp(BIN, y) = %d\n", strcmp(BIN, y));
	printf("strncmp(BIN, y, 4) = %d\n", strncmp(BIN, y, 4));
	printf("memcmp(BIN, y, 4) = %d\n", memcmp(BIN, y, 4));
	printf("--------------\n\n");

	/*
	 * and now demonstrate memset
	 */
	memset(x, 'a', 3);
	printit("memset(x, 'a', 3) sets x =", x, 4);
	putchar('\n');
	printf("--------------\n\n");

	/*
	 * this may or may not work
	 * the problem is we're copying an array into itself, offset by 4
	 */
	strcpy(x, NUM);
	strcpy(y, NUM);
	printit("For this, x =", x, 4);
	printit(" and y =", y, 4);
	putchar('\n');
	memcpy(x, &x[1], 2);
	strncpy(y, &y[1], 2);
	printit("memcpy(x, &x[1], 2) sets x =", x, 4);
	putchar('\n');
	printit("strncpy(y, &y[1], 2) sets y =", y, 4);
	putchar('\n');
	printf("--------------\n\n");

	/*
	 * reset everything
	 */
	(void) strcpy(x, NUM);
	(void) strcpy(y, NUM);
	printit("Resetting, x =", x, strlen(x));
	printit(" and y =", y, strlen(y));
	putchar('\n');

	/*
	 * `now we look for characters
	 */
	printf("Find the first and last ocurrence of a character\n");
	z1 = strchr(x, '1');
	printf("strchr(x, '1') = %s", z1 == NULL ? "NULL" : z1);
	if (z1 == NULL) putchar('\n');
	else printf(" (that's index %d)\n", (int)(z1 - x));
	z2 = strrchr(x, '1');
	printf("strrchr(x, '1') = %s", z2 == NULL ? "NULL" : z2);
	if (z2 == NULL) putchar('\n');
	else printf(" (that's index %d)\n", (int)(z2 - x));
	printf("--------------\n\n");

	/*
	 * now we look substrings
	 */
	printf("Find the first occurrance of a substring\n");
	z1 = strstr(x, "34");
	printf("strstr(x, \"34\") = %s", z1 == NULL ? "NULL" : z1);
	if (z1 == NULL) putchar('\n');
	else printf(" (begins at index %d)\n", (int)(z1 - x));
	printf("--------------\n\n");

	/*
	 * now break a string into tokens
	 */
	(void) strcpy(x, LINE);
	printit("Resetting, x =", x, strlen(x));
	putchar('\n');
	printf("It's from a csv file ... grab each field\n");
	i = 0;
	z1 = strtok(x, ",");
	while(z1 != NULL){
		printf("Field %2d: \"%s\"\n", i, z1);
		i += 1;
		z1 = strtok(NULL, ",");
	}
	printf("Done!\n");
	printf("--------------\n\n");
	
	/* finissimo! */
	return(0);
}

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu

ECS 36A, Programming & Problem Solving Version of April 2, 2024 at 12:13PM

You can get the raw source code here.