CODEWITHSUNDEEP
ctexttabsspace
Omid
Omid

Reputation: 2667

Removing spaces from the two sides of a text line

I am supposed to write a simple program that strips the lines of their trailing spaces and tabs. It should be written with the most basic tools in C (No pointers and libraries).

/* Write a program to remove trailing blanks and tabs from each
line of input, and to delete entirely blank lines. */

#include <stdio.h>
#define MAXLINE 1000

int gettline(char s[], int lim);
void inspect_line(char s[], int limit, int start, int end);

main()
{
    int len, i, start, end;
    start = 0;
    end = MAXLINE;
    char line[MAXLINE];
    while ((len = gettline(line, MAXLINE)) > 0){
            inspect_line(line, MAXLINE, start, end);
            for(i=start; i<end-1;++i)
                printf("%c",line[i]);
        }
    printf("\n");   
    return 0;
}

/* gettline: read a line into s, return length */
int gettline(char s[], int lim)
{
    int c, i;
    for (i=0; i<lim-1 && (c=getchar())!=EOF && c!='\n'; ++i)
        s[i] = c;
    if (c == '\n'){
        s[i] = c;
        ++i;
    }
    s[i] = '\0';
    return i;
}

/* inspect_line: determines the indices to the start and the end of the sentence */
void inspect_line(char s[], int limit, int start, int end)
{
    while((s[start]!=' ') && (start<limit-1))
        ++start;
    while(!(s[end]>=33 && s[end]<=126))
        --end;
}

when I run it, I get a strange result:

enter image description here

I am not sure what the problem is and I have been trying to debug it for hours with no result.

Upvotes: 1

Views: 53

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726669

Here is what is going on: when you write

inspect_line(line, MAXLINE, start, end);
for(i=start; i<end-1;++i)
    printf("%c",line[i]);

you assume that the values set to start and end inside inspect_line function would be transferred to main; that assumption is incorrect. In C parameters are passed by value. That is why start and end remain what they were before the call.

You can fix this by passing pointers to start and end into the inspect_line function. Of course you would need to change the function to accept and use pointers, too:

void inspect_line(char s[], int *start, int *end)
{
    while(isspace(s[*start]) && (*start < *end))
        ++(*start);
    while(isspace(s[*end]) && (*start < *end))
        --(*end);
}

the call would look like this:

// Note that passing MAXLINE is no longer necessary
inspect_line(line, &start, &end);
for(i=start ; i <= end-1 ; ++i) // both start and end are inclusive
    printf("%c",line[i]);

You would also need to re-initialize start and end between each iteration of the loop, setting start to zero and end to the current value of len.

Upvotes: 2

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