Remove extra whitespace from a string in C

问题:

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;
}

回答1:

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;
}

回答2:

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;
}

回答3:

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

回答4:

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.

回答5:

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$

回答6:

The problem:

1. You are tracking the '\t' tab, but you have to remove the spaces.
   
2. Also, you are tracking and finding the '\t', but you have no steps to removing it (I added one).
   
3. 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.
4. 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;
}

回答7:

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;
}