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

Question

Well I'm looking for a function that reduce multiple spaces in a string.

For example for string s given :

s="hello__________world____!"

The function must return "hello_world_!"

In python we can do it via regexp simply as:

re.sub("\s+", " ", s);

Answer 1

There is no such function in the C standard library. One must write a function to do so or use a third-party library.

The following function should do the trick. Use the source string as the destination pointer to perform the operation in place. Otherwise, ensure that the destination buffer is sufficiently sized.

void
simplifyWhitespace(char * dst, const char * src)
{
    for (; *src; ++dst, ++src) {
        *dst = *src;
        if (isspace(*src))
            while (isspace(*(src + 1)))
                ++src;
    }

    *dst = '\0';
}

Answer 2

void remove_more_than_one_space(char *dest, char *src)
{
    int i, y;
    assert(dest && src);
    for(i=0, y=0; src[i] != '\0'; i++, y++) {
        if(src[i] == ' ' && src[i+1] == ' ') {
            /* let's skip this copy and reduce the y index*/
            y--;
            continue;
        }
        /* copy normally */
        dest[y] = src[i];
    }
    dest[y] = '\0';
}
int main()
{
    char src[] = "Hello   World   ! !!   !";
    char dest[strlen(src) + 1];
    remove_more_than_one_space(dest, src);

    printf("%s\n", dest);
}

I just made this, hope it helps.

Answer 3

A version that modifies the string in place, run it on a copy if the original must be preserved:

void compress_spaces(char *str)
{
        char *dst = str;

        for (; *str; ++str) {
                *dst++ = *str;
                if (isspace(*str)) {
                        do ++str; while (isspace(*str));
                        --str;
                }
        }
        *dst = 0;
}