How to get substring in C : c, substring

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01.04.2005 at 03:08AM PST, ID: 21260896

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7.0

How to get substring in C

Zone: C Programming Language

Tags: c, substring

How to get substring in C

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Question Stats

Zone: Programming

Question Asked By: priyashree

Solution Provided By: rstaveley

Participating Experts: 5

Solution Grade: A

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01.04.2005 at 03:26AM PST, ID: 12951168

Jase-Coder:

hi try
strchr(char *str, int ch)

for example

#inlucde <string.h>

void main()
{
*p;

p = strchr("This is a test", ' ') // p holds "is a test"
}

01.04.2005 at 03:27AM PST, ID: 12951169

Jase-Coder:

better still use strstr(char *str1, char *str2)

01.04.2005 at 03:59AM PST, ID: 12951310

msjammu:

I can use strncpy() somehow

01.04.2005 at 04:47AM PST, ID: 12951588

rstaveley:

char* points to an array of characters. Conventionally in C, there is an ASCII 0 ('\0') character in character arrays to denote the end.

If, say, you declare,

char *p = "abcd";

your p character pointer points to an array of 5 (yes 5) characters, the last of which is '\0'.

If you wanted to point to "bc", you might be tempted to do something like...

char p2 = p+1;

However, most C library functions expect you to '\0'-terminate the string, which means that p2 would be pointing to "bcd".

That's why you generally need to copy your substring into a separate character array and then copy a '\0'-terminator into it.

This illustrates the point:

--------8<--------
#include <stdio.h>
#include <string.h>

int main()
{
      char *src = "abcd";
      char *dst = "01234";

      strncpy(dst,src+1,2); /* Copy a substring of two characters from src into dst, starting from the 2nd character in src */
      printf("dst is \"%s\"\n",dst);
}
--------8<--------

See the output?

--------8<--------
dst is "bc234"
--------8<--------

Accepted Solution

01.04.2005 at 04:51AM PST, ID: 12951613

Jase-Coder:

I think strncpy() is a c++ function that has a defult parameter, which is the length of the string.

01.04.2005 at 04:51AM PST, ID: 12951614

rstaveley:

NB: you'll get a core dump with that on Linux though, because you are copying data to read-only memory.

Better to write:
--------8<--------
#include <stdio.h>
#include <string.h>

int main()
{
char src[] = "abcd";
char dst[] = "01234";

strncpy(dst,src+1,2);
printf("dst is \"%s\"\n",dst);
}
--------8<--------

That way the src and dst strings are copied into the stack, which you are allowed to write to.

Windows is less discriminating :-)

01.04.2005 at 04:52AM PST, ID: 12951623

rstaveley:

> I think strncpy() is a c++ function that has a defult parameter, which is the length of the string

Nope, strncpy is part of the C library. You are thinking of the C function strcpy, which copies the entire string.

01.04.2005 at 07:21AM PST, ID: 12952776

Mysidia:

You can copy the right pieces to a new buffer space to get a substring:

Where 'buffer' is of length greater than start-end+1

char* substring_r(char* buffer, char* str, int start, int end)
{
int i, x = 0;

for(i = start ; i <= end; i++)
buffer[x++] = str[i];
buffer[x] = '\0';

return temp;
}

Assisted Solution

01.04.2005 at 08:22AM PST, ID: 12953548

madhurdixit:

String in C is simply array of characters terminated by '/0' .

If you are searching for a particular substring you can compare them through indexing.

If you want a substring say , from length 5 to 10 ,
you can start indexing from 5 and go on 10 and every time read it on to another character array.
This is pretty much done in answer above by "Mysidia".

01.04.2005 at 10:25AM PST, ID: 12954795

Mysidia:

return temp;

would really be
return buffer;

to use this approach you need the offsets, and you need to set aside a buffer, i.e.

int main()
{
char temp[25];

substring_r(temp, 1, 6, "!Hello there...");
printf("%s\n", temp);
}

if you're willing to destroy the original string, then it's even easier..

just null terminate where you want it to stop, and move the start of
the substring to the start of the array.

int main()
{
char temp[25] = "!Hello there...";

memmove(temp, temp+1, 6); /* the 6 is how many bytes to copy starting from the source string
and ending at (temp+1)[5] */
temp[6] = '\0'; /* End the result*/

printf("%s\n", temp);
}

01.28.2005 at 09:20PM PST, ID: 13170114

jmcg:

No comment has been added to this question in more than 21 days, so it is now classified as abandoned.

I will leave the following recommendation for this question in the Cleanup topic area:
Split: rstaveley {http:#12951588} & Mysidia {http:#12952776}

Any objections should be posted here in the next 4 days. After that time, the question will be closed.

jmcg
EE Cleanup Volunteer

02.02.2005 at 12:58AM PST, ID: 13201121

modulo:

Forced accept.

modulo
Community Support Moderator

20080236-EE-VQP-29