C ++：摆脱char数组中的char

Question

I am creating little function that will see if char in char array is a space. If it is, it will delete the space. So far I have:

void clean(char* n, int size){
for (int i = 0; i<size; i++){
        if (n[i]==' '){
            n[i]= '';
        }
}

};

However, I get an error:

warning: empty character constant [-Winvalid-pp-token]

My question is: how can I, withouth any libraries, get rid of the space in an char array. What should I put here:

n[i]= ____ 

Thanks!

Answer 1

When you find a space you need to shuffle the rest of the string to the left.

So the code you need is (assuming null terminated strings)

void clean(char* n) {
   for (int from = 0, to = 0; n[from]; ++from) {
     if (n[from] != ' ') {
        n[to] = n[from];
        ++to;
     }
   }
   n[to] = 0;
}

This will copy the string to itself, removing spaces along the way

Answer 2

Don't confuse string constants and character constants:

"h"

is a string constant containing one character, plus a NULL character to mark termination.

'h'

is a character constant, it is one character, no more no less.

In C++ "" is indeed an empty string, but '' is invalid syntax since a character necessarily has a value.

Removing a single character from a string is more involved than this.

If you have for example a string like this:

"foo bar"

Removing the space character actually consists in shifting all subsequent characters to the left.

"foo bar"
    ^
    |
    +- bar\0

And do not forget to also move the final NULL character ('\\0') so that the string ends correctly after 'r'.

Answer 3

If you recall that C++ standard algorithms work perfectly well with arrays, then the most elegant solution to this problem is std::remove . Here is an example:

#include <algorithm>
#include <iostream>
#include <string.h>

void clean(char* n, int size) {
    std::remove(n, n + size, ' ');
}

int main() {
    char const* test = "foo bar";
    // just some quick and dirty modifiable test data:
    char* copy = new char[strlen(test) + 1];
    strcpy(copy, test);

    clean(copy, strlen(copy) + 1);

    std::cout << copy << "\n";

    delete[] copy;
}

Note that the array does not actually shrink in size. If you need actual shrinking, then you need to allocate memory for a new array, copy the requirements elements to it and release memory for the old one.

---

Of course, in real code you should not use dynamic arrays in the first place but use std::string :

#include <algorithm>
#include <iostream>
#include <string>

void clean(std::string& n) {
    n.erase(std::find(n.begin(), n.end(), ' '));
}

int main() {
    std::string test = "foo bar";
    clean(test);
    std::cout << test << "\n";
}