Changing a piece of a character array into an integer array in C

Question

I am looking through a data file containing both words and numbers, and I need to take the numbers out of each row and store them in an array.

Cheryl 2 1 0 1 2 0  
Neal 0 0 2 0 2 0  
Henry 0 2 2 0 2 0  
Lisa 0 0 0 0 2 1

This is how the file is formatted. I start by inputting each line into an array, participants[], and then I need to take the numbers from each line and put them in a separate, two-dimensional array, individually. i.e. the first line would be translated to:

responses[0][0] = 2
responses[0][1] = 1
responses[0][2] = 0
responses[0][3] = 1
responses[0][4] = 2
responses[0][5] = 0

At this point, I detect the first space with char *pointer = strstr(" ", participants[]);, and am able to locate the the beginning of the numbers with strcpy(temp, pointer+1);.
From that point, I run into problems as I am having a hard time translating the string of numbers (still a char string), into individual integer values to be stored in my responses[][] array.

Thanks!

Try strtoul(). That might even take care of the tokenization for you if you play it right. — Kerrek SB
– Kerrek SB, Commented Nov 8, 2011 at 22:50
1) read the manual, 2) perhaps you can use the optional endptr argument to figure out where the next number starts. — Kerrek SB
– Kerrek SB, Commented Nov 8, 2011 at 22:52

AusCBloke · Accepted Answer · 2011-11-09 01:33:53Z

1

If that's you're exact format, then perhaps fscanf/sscanf could do the job for you? ie.

#include <stdio.h>

int main(void)
{
   int nums[6]; 
   char line[] = "Cheryl 2 1 0 1 2 0";

   sscanf(line, "%*s %d %d %d %d %d %d", &nums[0], &nums[1], &nums[2], &nums[3], &nums[4], &nums[5]);

   printf("%d %d %d %d %d %d\n", nums[0], nums[1], nums[2], nums[3], nums[4], nums[5]);

   return 0;
}

Output:

2 1 0 1 2 0

And then just check the return value to make sure the right amount of numbers were read.

EDIT: For an arbitrary amount:

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

char *strchr_ignore_start(const char *str, int c)
{
   if (c == '\0') return strchr(str, c); /* just to be pedantic */

   /* ignore c from the start of the string until there's a different char */
   while (*str == c) str++;

   return strchr(str, c);
}

size_t extractNums(char *line, unsigned *nums, size_t num_count)
{
   size_t i, count;
   char *endptr = line;

   for (i = 0, count = 0; i < num_count; i++, count++) {
      nums[i] = strtoul(line, &endptr, 10);
      if (line == endptr) /* no digits, strtol failed */
         break;

      line = endptr;
   }

   return count;
}

int main(void)
{
   unsigned i, nums[9];
   char line[] = "Cheryl 2 1 0 1 2 0 0 1 2";
   char *without_name;

   /* point to the first space AFTER the name (we don't want ones before) */  
   without_name = strchr_ignore_start(line, ' ');

   printf("%u numbers were successfully read\n",
          (unsigned)extractNums(without_name, nums, 9));

   for (i = 0; i < 9; i++)
      printf("%d ", nums[i]);

   putchar('\n');

   return EXIT_SUCCESS;
}

edited Nov 9, 2011 at 1:33

answered Nov 8, 2011 at 22:56

AusCBloke

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6 Comments

gkiar Over a year ago

I need the method to be extensible, so that if there are say, 9 options instead of six, it stores all 9. Is there a way to modify this to meet that criteria? However, what you gave me is exactly what I need other than that! :)

AusCBloke Over a year ago

@iKiar how will you be extracting the numbers? Will you have each line already read into a string before trying to extract the numbers? And are they signed or unsigned?

gkiar Over a year ago

Yes, the string would be something like char line[] = "Cheryl 2 1 0 1 2 0 0 1 2"; as opposed to char line[] = "Cheryl 2 1 0 1 2 0";.. Of course this can also go the other way and have a string like char line[] = "Cheryl 1 2 0";

gkiar Over a year ago

And the only possible values are 0,1,2. So although they aren't unsigned variable types, they aren't signed.

AusCBloke Over a year ago

@iKiar I edited it one more time, I didn't like the potential white space problem.

|

Dave · Accepted Answer · 2011-11-08 23:14:06Z

0

strtok() seems like the obvious solution here:

char buf[1024];
int y;
for(y=0;fgets(buf, sizeof buf, file); y++){
     strtok(buf, " "); //burn name;
     char *str;
     int x = 0;
     for(str=strtok(NULL, " "); str; str=strtok(NULL, " ")){
          responses[y][x++] =  atoi(str);
     }
}

answered Nov 8, 2011 at 23:14

Dave

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