Truncating Spaces in a given string

Question

Input- Hello World

output- HelloWorld

This is program i have written in c.

But i get segmentation fault.

The logic i have used is, when i found a space i swap that with next character till end then insert a '\0' character

#include <stdio.h>

int main()    
{    
        char s[12]="Hello World";    
        char *t;    
        t=s;    
        while(*t)    
        {    
                char *p;    
                p=t;    
                if(*p==' ')    
                {    
                        while(*p !='\0')    
                        {    
                                char x;    
                                x=*p;   
                                *p=*(p+1);    
                                *(p+1)=x;   
                                p++;    
                        }    
                        *(p-1)='\0';    
                }    
                t++;   
        }
        printf("%s\n",s);   
}

score 3 · Answer 1 · answered Aug 29 '13 at 20:40

3

K&R style copy:

#include <stdio.h>

int main()
{
        char s[12]="Hello World";
        char *src, *dst;
        for(src=dst=s; *dst = *src; src++) {
                if( *dst == ' ') continue;
                dst++;
                }
        printf("%s\n",s);
        return 0;
}

answered Aug 29 '13 at 20:40

wildplasser

43,142
8
66
109

1

+1 cuz it's a solution that would drive OOP types mad. – Jiminion Aug 29 '13 at 21:18
Well, it is just a variation on the K&R strcpy() (the continue can of course be avoided; it is only there for educational purposes ;-) – wildplasser Aug 29 '13 at 21:20
@Jim since OOP types would be reading a question on C? lol – Jonathan Henson Aug 29 '13 at 21:20

Jonathan Henson · Accepted Answer · 2013-08-29T20:34:06.907

1

swap out the nasty nested while loop with a call to this function.

void siftLeftAtCurrentPos(char* cstr)
{
   while(*cstr)
   {
     *cstr = *(cstr + 1);
      cstr++;
   }
}

then don't increment t until *p != ' '

edited Aug 29 '13 at 20:34

answered Aug 29 '13 at 20:27

Jonathan Henson

8,076
3
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52

now inside while loop i wrote *p=*(p+1);p++; thanks a lot...it worked ...but what was happening early...why did it show error..... – user2712068 Aug 29 '13 at 20:37
but i was using x as a char variable used to swap... – user2712068 Aug 29 '13 at 20:40
@user2712068 when you set (p+1)* to x, you lost your NULL on the last pass, that made your loop infinite. – Jonathan Henson Aug 29 '13 at 20:46
@user2712068 not to mention the fact that you overwrote your call-stack in the process... lol. – Jonathan Henson Aug 29 '13 at 20:54

Jiminion · Answer 3 · 2013-08-29T21:14:24.063

0

Just take out:

char x;    
x=*p;   
*(p+1)=x;

This is the problem.

edited Aug 29 '13 at 21:14

answered Aug 29 '13 at 20:39

Jiminion

5,080
1
31
54

why it is so..what actually happens if i do that – user2712068 Aug 29 '13 at 20:44
At that point, you already know that character will be overwritten. It became extra when you copied p+1 to p. – Jiminion Aug 29 '13 at 21:16

score 0 · Answer 4 · answered Aug 29 '13 at 20:44

Your inner while loop is an infinite loop. When you swap the space you end up making so that the next character will also be a space.

As mentioned in Jonathan's answer, you can fix this by just shifting things left instead of swapping the values. That said, you can make an even more efficient algorithm that removes spaces in a single pass, without nested loops. Your current algorithm will take quadratic time if you have a string that is full of spaces...

char* in = s; //next character to read;
char* out = s; //where to write the next non-space character;
//copy all the non spaces
while(*in){
   if(*in != ' '){
     *out = *in;
     out++;
   }
   in++;
}
//now fill the rest of the strings with null values:
while(out != in){
   *out = '\0';
   out++;
}

Truncating Spaces in a given string

4 Answers4