Sorting Strings
#include <stdio.h>
#include <string.h>
/* A Quicksort for strings. */
void quick_string(char items[][10], int count)
{
qs_string(items, 0, count-1);
}
int qs_string(char items[][10], int left, int right)
{
register int i, j;
char *x;
char temp[10];
i = left; j = right;
x = items[(left+right)/2];
do {
while((strcmp(items[i],x) < 0) && (i < right)) i++;
while((strcmp(items[j],x) > 0) && (j > left)) j--;
if(i <= j) {
strcpy(temp, items[i]);
strcpy(items[i], items[j]);
strcpy(items[j], temp);
i++; j--;
}
} while(i <= j);
if(left < j) qs_string(items, left, j);
if(i < right) qs_string(items, i, right);
}
char str[][10] = { "one",
"two",
"three",
"four"
};
int main(void)
{
int i;
quick_string(str, 4);
for(i=0; i<4; i++) printf("%s ", str[i]);
return 0;
}The functional approach to string sorting
/*
Beginning C: From Novice to Professional, Fourth Edition
By Ivor Horton
ISBN: 1-59059-735-4
640 pp.
Published: Oct 2006
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
bool str_in(const char **); /* Function prototype for str_in */
void str_sort(const char *[], int); /* Function prototype for str_sort */
void swap( void **p1, void **p2); /* Swap two pointers */
void str_out(char *[], int); /* Function prototype for str_out */
const size_t BUFFER_LEN = 256;
const size_t NUM_P = 50;
/* Function main - execution starts here */
int main(void)
{
char *pS[NUM_P]; /* Array of string pointers */
int count = 0; /* Number of strings read */
printf("\nEnter successive lines, pressing Enter at the end of"
" each line.\nJust press Enter to end.\n");
for(count = 0; count < NUM_P ; count++) /* Max of NUM_P strings */
if(!str_in(&pS[count])) /* Read a string */
break; /* Stop input on 0 return */
str_sort( pS, count); /* Sort strings */
str_out( pS, count); /* Output strings */
return 0;
}
/*******************************************************
* String input routine *
* Argument is a pointer to a pointer to a constant *
* string which is const char** *
* Returns false for empty string and returns true *
* otherwise. If no memory is obtained or if there *
* is an error reading from the keyboard, the program *
* is terminated by calling exit(). *
*******************************************************/
bool str_in(const char **pString)
{
char buffer[BUFFER_LEN]; /* Space to store input string */
if(gets(buffer) == NULL ) /* NULL returned from gets()? */
{
printf("\nError reading string.\n");
exit(1); /* Error on input so exit */
}
if(buffer[0] == "\0") /* Empty string read? */
return false;
*pString = (char*)malloc(strlen(buffer) + 1);
if(*pString == NULL) /* Check memory allocation */
{
printf("\nOut of memory.");
exit(1); /* No memory allocated so exit */
}
strcpy(*pString, buffer); /* Copy string read to argument */
return true;
}
/****************************************************
* String sort routine *
* First argument is array of pointers to strings *
* which is of type char*[]. *
* Second argument is the number of elements in the *
* pointer array - i.e. the number of strings *
****************************************************/
void str_sort(const char *p[], int n)
{
char *pTemp = NULL; /* Temporary pointer */
bool sorted = false; /* Strings sorted indicator */
while(!sorted) /* Loop until there are no swaps */
{
sorted = true; /* Initialize to indicate no swaps */
for(int i = 0 ; i<n-1 ; i++ )
if(strcmp(p[i], p[i + 1]) > 0)
{
sorted = false; /* indicate we are out of order */
swap(&p[i], &p[i+1]); /* Swap the pointers */
}
}
}
/****************************************************
* String output routine *
* First argument is an array of pointers to *
* strings which is the same as char** *
* The second argument is a count of the number of *
* pointers in the array i.e. the number of strings *
****************************************************/
void str_out(char *p[] , int n)
{
printf("\nYour input sorted in order is:\n\n");
for (int i = 0 ; i<n ; i++)
{
printf("%s\n", p[i]); /* Display a string */
free(p[i]); /* Free memory for the string */
p[i] = NULL;
}
return;
}
/******************************************
* Swap two pointers *
* The arguments are type pointer to void* *
* so pointers can be any type*. *
*******************************************/
void swap( void **p1, void **p2)
{
void *pt = *p1;
*p1 = *p2;
*p2 = pt;
}Enter successive lines, pressing Enter at the end of each line.
Just press Enter to end.
a
s
d
s
s
s
d
s
d
sd
sd
sd
Your input sorted in order is:
a
d
d
d
s
s
s
s
s
sd
sd
sd
