extract substring from string in C

baddah · 04-07-2006, 06:09 AM

hallo,is there no function in C (like substr in PHP) to extract a substring from one string into another.for instance if I have

char string1[10];

if string1 = '12345678' how can i store '34567' into another string(in PHP substring(string1,3,4) would have worked.)

thanks

Flesym · 04-07-2006, 06:45 AM

Of course you can do this in C. Have a look at the following link where you will find all standard C string functions:
http://www.cppreference.com/stdstring/index.html
For your purpose you should use the function 'strncpy'
Here an example:

Code:

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

main(){
  const char* from = "12345678";
  char *to = (char*) malloc(6);
  strncpy(to, from+2, 5);
}

baddah · 04-07-2006, 07:35 AM

thanks,that worked!although i must confess i'm a bit rusty on the whole C pointer thing.I'll just use it for now,figure out the details later..

charleykadet · 10-18-2008, 03:37 PM

You have to put '\0' at the end of the string...

bgeddy · 10-19-2008, 12:05 PM

Quote:

You have to put '\0' at the end of the string...

Yeah - but using strndup you don't have to worry about null termination as it adds it and allocating memory as it does the malloc for you so ..

Code:

#include <string.h>

main(){
  const char* from = "12345678";
  char *to;
  to=strndup(from+2, 5);
}

dwhitney67 · 10-19-2008, 12:56 PM

You also have to free any allocated memory, including if you use strdup().

Here's another take on what otherwise should have been a simple exercise:

PHP Code:


			
#include <string.h>

#include <stdlib.h>

#include <stdio.h>



char* substring(const char* str, size_t begin, size_t len)

{

  if (str == 0 || strlen(str) == 0 || strlen(str) < begin || strlen(str) < (begin+len))

    return 0;



  return strndup(str + begin, len);

}





int main()

{

  size_t      begin  = 5;

  size_t      end    = 10;



  const char* str    = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

  char*       substr = substring(str, begin, end);



  printf("str    = %s\n", str);

  printf("substr starting from pos %u, and %u characters in length...\n", begin, end);

  printf("substr = %s which has a strlen of %u\n", substr, strlen(substr));



  free(substr);



  return 0;

}

aryagaurav001 · 02-02-2010, 05:22 AM

//simple program to extract substring from a given string

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

void extract(char *,char *,char *,int,int);
void main()
{

char s[50]="working with strings is fun";
char t[50];
char d[50];
int pos,len;

printf("enter the position and length to be extracted= ");
scanf("%d%d",&pos,&len);

printf("\n\n");
extract(s,t,d,pos,len);
puts(d);
getch();
}
void extract(char *s,char *t,char *d,int pos,int len)
{

s=s+(pos-1);
t=s+len;
while(s!=t)
{
*d=*s;
s++;
d++;
}
*d='\0';

}

email id:-aryagaurav_dce_cs@yahoo.co.in