Remove extra whitespace from a string in C

Question

I have this string

"go    for    goa"

and the output should be

"go for goa"

I want to remove the extra spaces. That means two or more consecutive spaces should be replaced with one space. I want to do it using an in place algorithm.

Below is the code I tried but it doesn't work:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Function to remove spaces in an string array */
char *removeSpaces(char *str) {
  int  ip_ind = 1;
  /* In place removal of duplicate spaces*/
  while(*(str + ip_ind)) {
    if ((*(str + ip_ind) == *(str + ip_ind - 1)) && (*(str + ip_ind)==' ')) {
      *(str_ip_ind-1)= *(str + ip_ind);
    }
    ip_ind++;
  }
  /* After above step add end of string*/
  *(str + ip_ind) = '\0';
  return str;
}
/* Driver program to test removeSpaces */
int main() {
  char str[] = "go   for  go";
  printf("%s", removeSpaces(str));
  getchar();
  return 0;
}

recursion.ninja · Answer 1 · 2018-05-04T23:23:49.100

12

Most solutions seem needlessly complicated:

#include <ctype.h>
#include <stdio.h>

void strip_extra_spaces(char* str) {
  int i, x;
  for(i=x=0; str[i]; ++i)
    if(!isspace(str[i]) || (i > 0 && !isspace(str[i-1])))
      str[x++] = str[i];
  str[x] = '\0';
}

int main(int argc, char* argv[]) {
  char str[] = "  If  you  gaze   into  the abyss,    the   abyss gazes also   into you.    ";
  strip_extra_spaces(str);
  printf("%s\n",str);
  return 0;
}

edited May 04 '18 at 23:23

answered Jul 21 '13 at 18:34

recursion.ninja

5,377
7
46
78

@GiorgiMoniava, I fixed it – Victor Dec 15 '16 at 20:33
Great solution. – Tursko Feb 01 '20 at 23:09
Old, but still great! Thank you. – PageMaker Feb 04 '21 at 22:27

score 4 · Answer 2 · answered Jul 21 '13 at 08:04

I can't even tell what your function is trying to do. For one thing, the first time through, that -1 will access before the start of the string. Try something like:

char *removeSpaces(char *str) {
    char *inp = str, *outp = str;
    int prevSpace = 0;

    while (*inp) {
        if (isspace(*inp)) {
            if (!prevSpace) {
                *outp++ = ' ';
                prevSpace = 1;
            }
        } else {
            *outp++ = *inp;
            prevSpace = 0;
        }
        ++inp;
    }
    *outp = '\0';
    return str;
}

No it wont, because he initialized ip_ind as 1. – Muthu Ganapathy Nathan Jul 21 '13 at 08:07 — Muthu Ganapathy Nathan, Jul 21 '13 at 08:07

nj-ath · Answer 3 · 2013-07-21T08:05:53.177

1

You aren''t checking for a space.. You are checking for a tab. Replace \t with (I mean space..)

edited Jul 21 '13 at 08:05

answered Jul 21 '13 at 07:58

nj-ath

3,028
2
25
41

score 1 · Answer 4 · answered Jul 21 '13 at 08:12

Your if condition doesn't work. I will show you my code. It is similar to yours, by just using two pointers: back and front.

If front is not a space, or front is a space but back is not a space, you need to copy front to back+1.

char *removeSpaces(char *str)
{
    if (*str == '\0') return str;

    char *back = str;
    char *front = str + 1;
    /* In place removal of duplicate spaces*/
    while(*front != '\0')
    {
        if (*front != ' ' || *back != ' ')    // highlight
            *(++back) = *front;
        front++;
    }

    /* After above step add end of string*/
    *(back + 1) = '\0';

    return str;
}

Hope this may help you.

score 1 · Answer 5 · answered May 01 '20 at 20:59

Would tell best answer left space @end ? Here simple translation to JS:

function strip_extra_spaces(str) {
  var i, x;
  for (i = x = 0; str[i]; ++i)
    if (!isspace(str[i]) || (i > 0 && !isspace(str[i - 1])))
      str[x++] = str[i];
  str[x] = '\0';
  return str;
}

str = "  If  you  gaze   into  the abyss,    the   abyss gazes also   into you.    ";
console.log(
  strip_extra_spaces(str.split(""))
  .join("")
  .replace(/\0.+/g, "")
  .replace(/\s/g, '☐')
)

function isspace(c) {
  return c == ' ';
}

Looking for something similar in C# to compare multiple strings and made this - inspired by recursion.ninja's and similar C# answer to Efficient way to remove ALL whitespace from String? - also problematic - removed spaces completely.

public static string TrimAllWithInplaceCharArray(string a) {
    var len = a.Length;
    var srcA = a.ToCharArray();
    int dstIdxA = 0;
    int planSpace = 0;

    for (int i = 0; i < len; ++i) {
        var ch = srcA[i];
        switch (ch) {
            case '\u0020': case '\u00A0': case '\u1680': case '\u2000': case '\u2001':
            case '\u2002': case '\u2003': case '\u2004': case '\u2005': case '\u2006':
            case '\u2007': case '\u2008': case '\u2009': case '\u200A': case '\u202F':
            case '\u205F': case '\u3000': case '\u2028': case '\u2029': case '\u0009':
            case '\u000A': case '\u000B': case '\u000C': case '\u000D': case '\u0085':
                if (planSpace == 1) planSpace = 2;
                break;

            default:
                if (planSpace > 1)
                {
                    srcA[dstIdxA++] = ' ';
                }
                srcA[dstIdxA++] = ch;
                planSpace = 1;
                break;
        }
    }
    return new string(srcA, 0, dstIdxA);
}

Muthu Ganapathy Nathan · Answer 6 · 2013-07-21T08:40:16.220

The problem:

You are tracking the '\t' tab, but you have to remove the spaces.
Also, you are tracking and finding the '\t', but you have no steps to removing it (I added one).
Every-time you mustn't increment the ip_ind, you must inc, only when deletion is not done, because when deletion is done, that scenario will be equal to incremented.
Your scenario will fail for "", to avoid it, add a check parameter as below (Method 1) or else start from ip_ind from 0 as in (Method 2). (Thanks to @Lee Daniel Crocker)

Solution:

You could try like this.,

Method 1 : ip_ind starts from one.

/* Function to remove spaces in an string array */
char *removeSpaces(char *str)
{
  int  ip_ind = 1;
  char *ptr;

  if(*str)
    return str;

  /* In place removal of duplicate spaces*/
  while(*(str + ip_ind))
  {
    if ( (*(str + ip_ind) == *(str + ip_ind - 1)) && (*(str + ip_ind)==' ') )
    {
        ptr = str + ip_ind;
        //Functionality for removal of spaces.
        do{
           *(ptr-1) = *ptr;
        }while(*ptr++ != '\0');


    }
    else //Inc only if deletion is not done.
    ip_ind++;
  }

 /* After above step add end of string*/
  *(str + ip_ind) = '\0';

 return str;
}

Method 2 : ip_ind starts from zero.

char *removeSpaces(char *str)
{
  int  ip_ind = 0;
  char *ptr;
  /* In place removal of duplicate spaces*/
  while(*(str + ip_ind))
  {
    if ( (*(str + ip_ind) == *(str + ip_ind + 1)) && (*(str + ip_ind)==' ') )
    {
        ptr = str + ip_ind+1;

        do{
           *(ptr-1) = *ptr;
        }while(*ptr++ != '\0');


    }
    else
    ip_ind++;
  }

 /* After above step add end of string*/
  *(str + ip_ind) = '\0';

 return str;
}

Is it not possible to solve this without using that additional pointer ptr? — krrishna, Jul 21 '13 at 08:55
@krrishna No it is not because, your pointing the current position you need `ip_ind`., for traversing to the end you need atleast one variable. In this case it is `ptr` — Muthu Ganapathy Nathan, Jul 21 '13 at 09:32

score 0 · Answer 7 · answered Jul 21 '13 at 08:12

There you go:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* Function to remove spaces in an string array */
char *removeSpaces(char *str) {
  int  ip_ind = 0;
  while (*(str+ip_ind) != 0) {
    if (*(str + ip_ind++) == 32) {
      if (*(str + ip_ind) == 32) {
        int x=ip_ind;
        while (*(str + x +1) != 0) {
          *(str + x)= *(str + 1 + x++);
        }
        *(str + x)= 0;
        --ip_ind;
      }
    }
  }
  return str;
}
/* Driver program to test removeSpaces */
int main() {
  char str[] = "go   for  go";
  printf("%s\n", str);
  printf("%s\n", removeSpaces(str));
  char str2[] = "go     for  go for go";
  printf("%s\n", str2);
  printf("%s\n", removeSpaces(str2));
  return 0;
}

Output:

dda$ ./a.out
go   for  go
go for go
go     for  go for go
go for go for go
dda$

score 0 · Answer 8 · answered Jul 22 '16 at 17:28

Simple one for You

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char a[100];
int i,t,k;
scanf("%[^\n]s",a);
t=strlen(a);
for(i=0;i<t;)
{
    if((a[i]==' ')&&(a[i+1]==' '))
    {
        for(k=i+1;k<t;k++)
        {
            a[k]=a[k+1];
        }
        t=t-1;
    }
    else
        i++;
}
printf("%s",a);
return 0;
}

Remove extra whitespace from a string in C

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