Solution for Exercise 20-5

ex2005

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

int main()
{
    char *input1,*input2;
    char *i1,*i2;

    input1 = (char *)malloc(sizeof(char)*1024);
    input2 = (char *)malloc(sizeof(char)*1024);
    if(input1==NULL || input2==NULL)
    {
        puts("Unable to allocate buffer! Oh no!");
        exit(1);
    }

    puts("Type something long and boring:");
    fgets(input1,1023,stdin);

    puts("Copying buffer...");
    i1=input1; i2=input2;
    while(*i1 != '\n')
        *i2++=*i1++;
    *i2 = '\0';

    printf("Original text:\n\"%s\"\n",input1);
    printf("Duplicate text:\n\"%s\"\n",input2);

    return(0);
}

Notes

* Line 7 declares two char pointer variables I use in the code to copy the string, i1 and i2. That's because I want to keep the original locations in the input1 and input2 variables.

* The copying action takes place starting at Line 21 where both i1 and i2 are initialized. That's two statements on a single line.

* The while loop at Line 22 copies the text, setting up the condition to stop copying when the pointer *i1 contains the newline character.

* Line 23 is one of those "jam it all on one line" statements favored by many C programmers. It works because the pointer operator * binds more tightly to the pointer variable than the increment operator. So the effect is that a character is copied from pointer i1 to i2, then both pointers (the memory addresses) are incremented.

* Line 23 could be split up as follows:

while(*i1 != '\n') { *i2=*i1; i1++; i2++; }

Either solution is fine, or if you managed to duplicate the string in another manner, that's okay too.

* Line 24 is required to cap the second string with the null character, \0. Without that terminating character, the duplicate string display might include random characters. The variable i2 doesn't need to be incremented; after the while loop is complete, it automatically points to the end-of-string position where the null character needs to go.

* Here is sample output:

Type something long and boring: It was the best of times, it was the worst of times. Copying buffer... Original text: "It was the best of times, it was the worst of times. " Duplicate text: "It was the best of times, it was the worst of times."

* The net effect of the code is to remove the newline added by the fgets() function.

Exercise ex2006 →