Inserting characters in the middle of char array

Question

I have a char array filled with some characters. Let's say I have "HelloWorld" in my char array. (not string. taking up index of 0 to 9)

What I'm trying to do is insert a character in the middle of the array, and push the rest to the side to make room for the new character that is being inserted.

So, I can make the char array to have "Hello.World" in it.

char ch[15]; // assume it has "HelloWorld" in it
for(int i=0; i<=strlen(ch)-1; i++) {
    if(ch[i]=='o' && ch[i+1]=='W') {
        for(int j=strlen(ch)-1; j>=i+2; j--) {
            ch[j] = ch[j-1]; // pushing process?
        }
        ch[i+1] = '.';
        break;
    }
}

Would this work? Would there be an easier way? I might just be thinking way too complicated on this.

"Sorry, but I should re-question about this topic". Read [Writing the perfect question](http://tinyurl.com/so-hints) and that will help you get the answer you need. — johnsyweb, Feb 14 '12 at 23:11
related: http://stackoverflow.com/questions/9284916/how-to-push-char-array — amit, Feb 14 '12 at 23:11
@Johnsyweb: seems "different" question now for me. He asked for help, made some progress and is stuck again and asking how to solve it. — amit, Feb 14 '12 at 23:12

score 3 · Answer 1 · edited Nov 16 '15 at 18:23

3

You need to start the inner loop from strlen(ch) + 1, not strlen(ch) - 1, because you need to move the NULL-terminator to the right one place as well. Remember that strlen returns the length of the string such that string[strlen(string)] == '\0'; you can think of strlen as a function for obtaining the index of the NULL-terminator of a C-string.

edited Nov 16 '15 at 18:23

Brian

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answered Feb 14 '12 at 23:12

Seth Carnegie

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@Haxify I updated my answer to reflect your updated question. – Seth Carnegie Feb 14 '12 at 23:15

score 2 · Accepted Answer · answered Feb 14 '12 at 23:18

If you want to move all the characters up by one, then you could do it using memmove.

#include <string.h>

char ch[15];

int make_room_at = 5;
int room_to_make = 1;

memmove(
    ch + make_room_at + room_to_make,
    ch + make_room_at,
    15 - (make_room_at + room_to_make)
);

ouah · Answer 3 · 2012-02-14T23:17:39.940

1

Simply do:

#define SHIFT  1
char bla[32] = "HelloWorld";    // We reserve enough room for this example  
char *ptr = bla + 5;            // pointer to "World"    
memmove(ptr + SHIFT, ptr, strlen(ptr) + 1);  // +1 for the trailing null

edited Feb 14 '12 at 23:17

answered Feb 14 '12 at 23:12

ouah

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Mark Wilkins · Answer 4 · 2012-02-14T23:32:10.443

The initial starting value for the inner loop is one short. It should be something like the following. Note too that since the characters are moved to the right, a new null terminator needs to be added:

    ch[strlen(ch) + 1] = '\0';
    for(j=strlen(ch); j>=i+2; j--) {  // note no "-1" after the strlen

Edit As far as the "Is this a good way?" part, I think it is reasonable; it just depends on the intended purpose. A couple thoughts come to mind:

Reducing the calls to strlen might be good. It could depend on how good the optimizer is (perhaps some might be optimized out). But each call to strlen require a scan of the string looking for the null terminator. In high traffic code, that can add up. So storing the initial length in a variable and then using the variable elsewhere could help.
This type of operation has the chance for buffer overflow. Always make sure the buffer is long enough (it is in the OP).

score 0 · Answer 5 · answered Feb 14 '12 at 23:20

If you're going to manipulate a char array you shouldn't make it static. By doing this:

char ch[15];

you're hardcoding the array to always have 15 characters in it. Making it a pointer would be step 1:

char* ch;

This way you can modify it as need be.

Inserting characters in the middle of char array

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