CODEWITHSUNDEEP
cstringpointers
Tyler
Tyler

Reputation: 4709

Cut out section of string

I wouldn't mind writing my own function to do this but I was wondering if there existed one in the string.h or if there was a standard way to do this.

char *string = "This is a string";

strcut(string, 4, 7);

printf("%s", string); // 'This a string'

Thanks!

Upvotes: 4

Views: 16409

Answers (6)

ВелоКастръ
ВелоКастръ

Reputation: 4483

I already wrote the answer for a similar problem there https://stackoverflow.com/a/42283266/6003870. It suitable for common actions and based mainly the function strncpy() from the C standard library. But this problem could be solved by the function memmove() as mentioned the dead user @sharptooth.

The function str_slice_in_place() use the memmove() as base and has support for positive indexes.

int
str_slice_in_place(char str[], const int index_from, const int index_to)
{
    // a support for only positive indexes
    if (index_from < 0 || index_to < 0)
        return -1;

    int len = index_to - index_from;

    // "index_from" is more than "index_to"
    if (len < 0)
        return -1;

    memmove(str, str + index_from, len);
    str[len] = '\0';
    return 0;
}

I also show you a code of a function main() and examples how to use this function.

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

int
main()
{
    char line[] = "--------------------------------------";

    char str1[] = "Remember a good";
    char str2[] = "Remember a good";
    char str3[] = "Remember a good";
    char str4[] = "Remember a good";

    printf("|     Original     | Slice  | Result \n%s\n", line);

    printf("| %s | ", str1);
    str_slice_in_place(str1, 0, 8);
    printf("(%d, %d) | %s\n", 0, 8, str1);

    printf("| %s | ", str2);
    str_slice_in_place(str2, 3, 9);
    printf("(%d, %d) | %s\n", 3, 9, str2);

    printf("| %s | ", str3);
    str_slice_in_place(str3, 0, 1);
    printf("(%d, %d) | %s\n", 0, 1, str3);

    printf("| %s | ", str4);
    str_slice_in_place(str4, 1, 1);
    printf("(%d, %d) | %s\n", 1, 1, str4);

    puts(line);

    return 0;
}

An output

|     Original     | Slice  | Result 
--------------------------------------
| Remember a good | (0, 8) | Remember
| Remember a good | (3, 9) | ember 
| Remember a good | (0, 1) | R
| Remember a good | (1, 1) | 
--------------------------------------

A testing environment

$ gcc --version
gcc (Debian 4.9.2-10) 4.9.2
Copyright (C) 2014 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
$ lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux 8.6 (jessie)
Release:    8.6
Codename:   jessie
$ uname -a
Linux localhost 3.16.0-4-amd64 #1 SMP Debian 3.16.36-1+deb8u2 (2016-10-19) x86_64 GNU/Linux

Upvotes: 0

che
che

Reputation: 12273

You can just tell printf to cut the interesting parts out for you:

char *string = "This is a string";
printf("%.*s%s", 4, string, &string[7]); // 'This a string'

:-)

Upvotes: 4

PTBNL
PTBNL

Reputation: 6130

You may be able to accomplish what you want and avoid writing a new function with a combination of strncpy and strcat:

#include <stdio.h>
#include <string.h>
int main(void)
{
  char   newStr[10];
  char   origStr[] = "This is a string";
  strncpy(newStr, origStr, 4);
  strcat(newStr, &origStr[7]);
  printf("newStr = %s\n", newStr);
  return(0);
}

For me, this outputs "This a string" (quotes mine), using Borland's free command line compiler on Windows XP. You can check out string.h at: http://opengroup.org/onlinepubs/007908799/xsh/string.h.html

Upvotes: 0

sharptooth
sharptooth

Reputation: 170549

Use memmove to move the tail, then put '\0' at the new end position. Be careful not to use memcpy - its behaviour is undefined in this situation since source and destination usually overlap.

Upvotes: 7

Uri
Uri

Reputation: 89839

If you're talking about getting rid of the middle of the string and moving the rest earlier in place, then I don't think there's a standard library function for it.

The best approach would be to find the end of the string, and then do an O(cut_size) cycle of shifting all the characters to the new location. In fact, there's a similar common interview question.

You have to be careful about using things like memory copy since the destination buffer overlaps with the source.

Upvotes: 1

Suroot
Suroot

Reputation: 4423

If you are doing this in C and know the offset then it's pretty simple.

char string[] = "my string";
char *substring;
substring = &string[2];

printf("%s", substring);

EDIT: If you wanted to shift the string.

char string[] = "my string";

int i = 0;
int offset = 2;

for( i = 0; string[i+offset] != '\0'; i++ ) {
 string[i] = string[i + offset];
}
string[i] = '\0';

Upvotes: -1

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