replace two consecutive spaces with one space in c

Question

Possible Duplicate:
How do I replace multiple spaces with a single space in C?

I have a string in c that can contain two consecutive spaces. I want to remove two consecutive spaces with one space. How can I do that? Help please.

Answer 1

If it is the case that there is a single occurrence of two consecutive spaces in the string then a possibility would be to use strstr() and memmove():

#include <stdio.h>
#include <string.h>

int main()
{
    char s[] = "a string with two  spaces";
    char* two_spaces_ptr = strstr(s, "  ");
    printf("[%s]\n", s);
    if (two_spaces_ptr)
    {
        memmove(two_spaces_ptr + 1,
                two_spaces_ptr + 2,
                strlen(two_spaces_ptr + 2) + 1); /* +1 to copy the NULL. */

    }
    printf("[%s]\n", s);

    return 0;
}

Output:

[a string with two  spaces]
[a string with two spaces]

The C standard for memmove() states:

The memmove function copies n characters from the object pointed to by s2 into the object pointed to by s1. Copying takes place as if the n characters from the object pointed to by s2 are first copied into a temporary array of n characters that does not overlap the objects pointed to by s1 and s2, and then the n characters from the temporary array are copied into the object pointed to by s1.

EDIT:

Updated answer to use memmove(), instead of strcpy() that resulted in undefined behaviour.

Answer 2

You can use strchr function to search for a space in a string and then follow it up with a logic to replace all the spaces following it. You need to repeat this for another patch of spaces till the string ends.

Answer 3

You can write over your own string:

char *ys = YOUR_STRING;
char *n = ys;
while (*ys)
{
  *n = *ys;
  if (*ys == ' ')
    while (*ys == ' ')
      ys++;
  else
    ys++;
  n++;
}

Or you can create a new string:

char *ys = YOUR_STRING;
char *n = malloc(sizeof(*n) * strlen(ys));
int i = 0;

while (*ys)
{
  n[i++] = *ys;
  if (*ys == ' ')
    while (*ys == ' ')
      ys++;
  else
    ys++;
}
// use n

Answer 4

for (unsigned char *p = YOUR_STRING, *q = p; ((*q = *p));) {
        if (*q++ == ' ') {
                while (*++p == ' ');
        } else {
                p++;
        }
}

Less obscure alternative:

unsigned char *p = YOUR_STRING;
unsigned char *q;
/* zap to the first occurrence */
while (*p && *p++ != ' ');
/* copy from here */
q = --p;
while ((*q = *p)) {
        if (*q++ == ' ') {
                while (*++p == ' ');
        } else {
                p++;
        }
}

Answer 5

If you're sure there can be only two spaces consecutive at max, you can do something like:

int main ()
{
    char *str="This  is a  wonderful world. Let's  have a   good  time here.";
    int len=strlen(str);
    char *result = (char*)malloc(len);
    int j=0;
    for(int i=0;i<len;i++) {
        if(str[i]==' ' && str[i-1]==' ') {
            i++;
        }
        result[j++]=str[i];
    }
    result[j]='\0';
    printf("%s\n", result);
  return 0;
}