Removing characters from original string?

Question

This may be basic, please be patient with me,

char data[]="(xxx)";

I would like to remove the () and leave data only to be xxx ,

char *p = strtok(data,"(");
p = strtok(NULL,")");
printf("this data: %s \n",p);
printf("this data: %s \n",data);

p should be xxx but its NULL , data stay the same (strtok should affect the source?)
this will not change data, I would like a way to manipulate data to be xxx

@layzak take a any word with () and just remove the () from the original word. — Curnelious, Jul 31 '16 at 14:07

Some programmer dude · Answer 1 · 2016-07-31T14:44:11.047

3

How about

memmove(data, data + 1, sizeof data - 1);  // Removes the (
data[strlen(data) -1] = '\0';  // Removes the )

Note that the above solution only works on the data as initially presented, with a leading and trailing parentheses. It also only works if data is actually an array and not a pointer. And the array data needs to be in modifiable memory (e.g. RAM).

Also note that is the requirements in the paragraph is met, then the order of the two statements doesn't matter.

edited Jul 31 '16 at 14:44

answered Jul 31 '16 at 14:04

Some programmer dude

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What about `a(xxx)b` ? a3f mentioned not elegant but acceptable – Soner from The Ottoman Empire Jul 31 '16 at 14:13
Thanks I can't use memmove its a micro processor environment, any other option ? – Curnelious Jul 31 '16 at 14:16
look at my comment @Curnelious are you kiddy boy oh my gosh – Soner from The Ottoman Empire Jul 31 '16 at 14:16
@snr Not part of the original question. Only added as a comment by the OP. :) – Some programmer dude Jul 31 '16 at 14:16
1

@Curnelious Using `memmove` will work ousing any standard-compliant C compiler. It won't work if the array is in some kind of read-only memory. You need to be *specific* when writing questions, including environments, *all* requirements, limitations etc. – Some programmer dude Jul 31 '16 at 14:18
@JoachimPileborg sorry, thanks I am checking if this solution will work. – Curnelious Jul 31 '16 at 14:21

M.Ferru · Answer 2 · 2016-07-31T14:09:15.090

1

It's a char[], not string. You can try something like this :

char new_Data[sizeof(data)/sizeof(char)];
for(i=1 ; i < sizeof(new_Data) ; i++){
        new_Data[i] = data[i];
}

This may work only if "(" and ")" are at the end of your char*

edited Jul 31 '16 at 14:09

answered Jul 31 '16 at 14:06

M.Ferru

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"It's a char*, not a string." 1) OP never mentioned either of those, so what are you talking about? 2) It's not a `char*`, it's a `char[]`. Huge difference. – Jul 31 '16 at 14:08
Sorry. I just edit my post – M.Ferru Jul 31 '16 at 14:11
thanks, this is not answering my question , its a new var, and also why strtok not affecting data? – Curnelious Jul 31 '16 at 14:14

a3f · Accepted Answer · 2016-07-31T14:46:17.880

1

char *in_parens(char* str) {
   char *end, *start;
   if (!(end = strrchr(str, ')'))) return NULL;
   if (!(start = strchr(str, '('))) return NULL;
   *end = '\0';
   return start + 1;
}

int main(void) {
    char data[] = "a(x(b)x)c";
    printf("%s\n", in_parens(data)); // prints x(b)x
}

Returns NULL if string doesn't contain a () pair. Otherwise, strips outermost pair and returns what's inside.

edited Jul 31 '16 at 14:46

answered Jul 31 '16 at 14:29

a3f

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great thats what I needed, so just call it and pass data ? how would I change original "Data" array with this ? – Curnelious Jul 31 '16 at 14:36
Yes, but keep in mind that `str` is modified. – a3f Jul 31 '16 at 14:41
I am not sure how to use that to change data.. – Curnelious Jul 31 '16 at 14:42
data= in_parens(data) ? – Curnelious Jul 31 '16 at 14:42
Added an example usage. – a3f Jul 31 '16 at 14:46
@a3f thank you very much. I know its basic stuff, but why are you return a value and not just assign str ? – Curnelious Jul 31 '16 at 14:50
@Curnelious `str` is local to in_parens. Arguments are passed by value in C. Check out this question: http://stackoverflow.com/questions/766893/how-do-i-modify-a-pointer-that-has-been-passed-into-a-function-in-c – a3f Jul 31 '16 at 14:53
@a3f your example btw is not removing the first "(" , try data="(a+5)"; – Curnelious Jul 31 '16 at 14:57
@snr People can downvote and do so. Your answer is ok though. @Curnelious `char data[] = "(a+5)";` works for me. – a3f Jul 31 '16 at 15:00

score 0 · Answer 4 · answered Jul 31 '16 at 15:03

Your code will not work because strtokdoes not work the way you think it does. When called the first time like this:

char *p = strtok(data,"(");

It will:

skip until the first char that's not a delimiter.
then try to find the next delimiter.
replace the last delimiter with a \0.
return a pointer to the first char of the token.

Since step two fails (there are no more delimiters) strtok will simply return NULL indicating that it didn't find any tokens. Any further calls to strtok for the same input will also return NULL.

You can change this by adding the ending delimiter in the first call like this:

char *p = strtok(data,"()");

Now strtok will find a token, and return a pointer to the first x in your example. Notice though, that since it only replaced the terminating delimiter with a \0, the opening parentesis is still present in data.

To get rid of that one you could do something like this:

char *p = strtok(data,"()");
strcpy(data, p);

However I would rather recommend building a new string for the results if you have any other content in the source data as well.

Soner from The Ottoman Empire · Answer 5 · 2016-07-31T14:22:23.560

The code takes two strings, which first is the complete one, the other is which characters to being deleted. You can specify like ()qwer.

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

char *strip_chars(const char *string, const char *chars)
{
    char * newstr = malloc(strlen(string) + 1);
    int counter = 0;

    for ( ; *string; string++) {
        if (!strchr(chars, *string)) {
            newstr[ counter ] = *string;
            ++counter;
        }
    }

    newstr[counter] = 0;
    return newstr;
}

int main()
{
    char *new = strip_chars("(xxx)", "()");
    printf("%s\n", new);

    free(new);
    return 0;
}

Removing characters from original string?

5 Answers5