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extract multidigits from a char* (substring)

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Join Date: Aug 2008

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monkey_king monkey_king is offline

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**extract multidigits from a char* (substring)**

Jul 1st, 2009

Hi,
given a cstring, I need to extract the digits in it, the digits are prefixed with either a '+' or '-'. Like

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
,.,.,.,+3ACT,.,.,.,.-12,.,.,.,.,.,.,.,actgncgt
#OUTPUT
3
12
,.,.,.,+3ACT,.,.,.,.-12,.,.,.,.,.,.,.,actgncgt
#OUTPUT
3
12

I've made a working program that does what I want,
but it seems overly complicated.
Does anyone have an idea if this can be done smarter, better, faster?

Thanks in advance

Btw I checked the program with valgrind and there are no leaks or errors

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
int main(){
  char tmp_array[100];
  const char* seq = "+1236,,..,,actgn+3ACT-4CCCC";
  printf("%s\n",seq);
 
  for(int i=0;i<strlen(seq);i++){
    if(seq[i]!='+'&&seq[i]!='-')
      continue;
    int j=i+1;
    while(j<strlen(seq)){
      if(seq[j]>='0' &&seq[j]<='9'){
	j++;
      }else
	break;
 
    }
    strncpy(tmp_array,seq+i+1,j-i-1);
    tmp_array[j-i-1]='\0';
    printf("numbers in substrings are: %d\n",atoi(tmp_array));
  }
 
  return 0;
}
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(){
  char tmp_array[100];
  const char* seq = "+1236,,..,,actgn+3ACT-4CCCC";
  printf("%s\n",seq);

  for(int i=0;i<strlen(seq);i++){
    if(seq[i]!='+'&&seq[i]!='-')
      continue;
    int j=i+1;
    while(j<strlen(seq)){
      if(seq[j]>='0' &&seq[j]<='9'){
	j++;
      }else
	break;
      
    }
    strncpy(tmp_array,seq+i+1,j-i-1);
    tmp_array[j-i-1]='\0';
    printf("numbers in substrings are: %d\n",atoi(tmp_array));
  }
  
  return 0;
}

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jephthah

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

•

Does anyone have an idea if this can be done smarter, better, faster?

check out: strtok() ... this breaks a string into tokens at each of one or more delimiters.

use it to break the string at each '+' or '-' (the delimiters), then check if the first one or more characters of each resulting string (the tokens) are numerals.

if it does, then push that number onto your result array. if it doesn't, skip on to the next token.

.

Last edited by jephthah; Jul 1st, 2009 at 7:33 pm. Reason: realized you dont want to save the + or -

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wildgoose

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

untested but here...

 Help with Code Tags 
 C Syntax (Toggle Plain Text) 
int main()
{
  char tmp_array[100];
  const char* seq = "+1236,,..,,actgn+3ACT-4CCCC";
  printf("%s\n",seq);
 
   while (*seq)
   {        // pre-scan for +-
      if (*seq != '-' && *seq != '+')
      {
         seq++;
         continue;
      }
 
      char *p = tmparray;
	  *p++ = *seq++;
 
      while (*seq)
	  {
	      if ((*seq < '0') || ('9' < *seq))
		  { 
		     break;
	      }
 
          *p++ = *seq++;
	   }
 
       *p = 0;
 
       printf("numbers in substrings are: %d\n",atoi(tmp_array)); 
  } 
 
  return 0;
}
int main()
{
  char tmp_array[100];
  const char* seq = "+1236,,..,,actgn+3ACT-4CCCC";
  printf("%s\n",seq);

   while (*seq)
   {        // pre-scan for +-
      if (*seq != '-' && *seq != '+')
      {
         seq++;
         continue;
      }

      char *p = tmparray;
	  *p++ = *seq++;

      while (*seq)
	  {
	      if ((*seq < '0') || ('9' < *seq))
		  { 
		     break;
	      }

          *p++ = *seq++;
	   }

       *p = 0;

       printf("numbers in substrings are: %d\n",atoi(tmp_array)); 
  } 

  return 0;
}

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wildgoose

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

But if allowed to use off the shelf library functions, then poster jephthah has the right idea!

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MrNoob

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

why dont you put an array with stuff you want and extract that to new array?

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wildgoose

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

Double the processing time. No optimal!

Why process a list twice when you can do it once!

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jephthah

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**Re: extract multidigits from a char* (substring)**

Jul 1st, 2009

wildgoose: posting "Untested" code on daniweb's C forum is generally risky business

anyhow, being able to use strtok() correctly is tricky for a new user. Also make sure you understand what is going on with strtol()

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
char string[100]="+1236,,..,,actgn+3ACT-4CCCC";
char *token, *ptr;
int value;
 
token = strtok(string,"+-");
printf ("found numbers: ");
 
while (token != NULL)
{	
	value = strtol(token,&ptr,10);
	if (ptr != token)
		printf(" %d,",value);
 
	token = strtok(NULL,"+-");
}
printf("\n");
char string[100]="+1236,,..,,actgn+3ACT-4CCCC";
char *token, *ptr;
int value;
	
token = strtok(string,"+-");
printf ("found numbers: ");
	
while (token != NULL)
{	
	value = strtol(token,&ptr,10);
	if (ptr != token)
		printf(" %d,",value);

	token = strtok(NULL,"+-");
}
printf("\n");

Last edited by jephthah; Jul 1st, 2009 at 8:02 pm.

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monkey_king monkey_king is offline

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**Re: extract multidigits from a char* (substring)**

Jul 2nd, 2009

Thanks ppl,
I need to keep track of the indices,
so the strtok approch wont work.

But thanks again.

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jephthah

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**Re: extract multidigits from a char* (substring)**

Jul 2nd, 2009

well, that's a nice bit of feature creep to throw out there at the last minute.

do you work in marketing?

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YrthWyndAndFyre YrthWyndAndFyre is offline

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**Re: extract multidigits from a char* (substring)**

#10

Jul 3rd, 2009

•

Originally Posted by monkey_king

Thanks ppl,
I need to keep track of the indices,
so the strtok approch wont work.

But thanks again.

The strtok() approach will work, just with a little added overhead - specifically, tracking the size of tokens you have already passed and either used or discarded.