删除额外的空格 C++

Question

I have the homework assignment where I should remove all leading spaces in the char array. If there is a space in the beginning of the array, it should be deleted too. Also, I have to take care about an empty array. I can't use <cstring> and <string.h> . Also, I can't create any additional arrays. I googled a lot, but I have no idea how to solve this problem. Here is what I have so far.

void clean(char* tab) 
{
    //char *p = tab;
    for (int i = 0; i <= sizeof(tab); i++) 
    {
        if ((tab[i] = ' ') && (tab[i + 1] = ' '))
        {
            tab[i] = tab[i + 1];
        }
    }
}

int main()
{
    char tab1[] = "   h qa  w e ";
    cout << tab1 << endl;
    clean(tab1);
    cout << tab1 << endl;
}

Will be very gratefull if someone can give me a hint how to figure it out.

Answer 1

Regard each space as a "free space" in the array, one which you should fill.

You can maintain two pointers to different places in your char array. One to the first available space, another to the currently character you examine.

You only need to figure out these questions:

1. How would you fill up the spaces?
2. How would you know when you're done?

Answer 2

You have a few separate problems here.

One is that you've mis-typed your comparisons: if ((tab[i] = ' ') && (tab[i+1] = ' ')) should undoubtedly be: if ((tab[i] == ' ') && (tab[i+1] == ' ')) .

Second, you're using sizeof(a pointer) , where you really wanted strlen(a pointer) (or at least something that works similarly, scanning for a NUL character that signals the end of the string).

Third, the algorithm your loop implements doesn't seem to reflect the intent of removing leading spaces very well (if at all). I'd scan for the first thing that wasn't a space, then copy the remainder of the string so it starts at the beginning of the string.

[Sorry, but I'm not going to post actual code or much more detail than that for a homework assignment.]

Answer 3

Those codes work with absolutely no dependency on nor and they don't allocate any temporary buffers. Note that a home made copy function must be defined to copy string content when a space is being removed.

Note that this code is easy to understand but may/should be optimized to minimize copies if performance is a requirement.

As it's unclear what you exactly want...

This one removes all spaces in the string.

#include <iostream>

void copy( char* to, char* from )
{
    int i = 0;
    while ( true ) // risky in case char* has no EOS character!
    {
        to[i] = from[i];
        if ( from[i] != '\0' )
            ++i;
        else
            break;
    }
}

void clean( char* tab ) 
{
    int i = 0;
    while ( tab[i] != '\0' )
    {
        if ( tab[i] == ' ')
        {
            copy( tab + i, tab + i + 1 );
            // do not increment i, to test tab[i] that was newly copied from tab[i+1]
        }
        else
        {
            ++i;
        }
    }

}

int main() {

    char tab1[] = "   h qa  w e ";
    std::cout << tab1 << std::endl;

    clean(tab1);

    std::cout << tab1 << std::endl;
}

https://ideone.com/Yv4aqL

If you only want to remove leading spaces , it's even easier, just change the clean function:

void clean( char* tab ) 
{
    int i = 0;
    while ( tab[i] == ' ' )
    {
        copy( tab + i, tab + i + 1 );
    }
}

https://ideone.com/RIAsGt