Thread: alphabetically sort textfile

ok so I can get realloc work for a 1d array.

but I'm fully confused with 2d arrays...

this is waht I need:
array[n][255]
while n iterates every single time a new line is read via
"while(fgets(puffer,LENGTH,filein))"

Code:

#include <stdio.h>
#include <stdlib.h>
#include <String.h>
#define LENGTH 255

int main()
{
    int i=0;
    char **str2d = malloc(sizeof(char*));
    str2d[0] = malloc(LENGTH*sizeof(char));
    FILE *filein;
    FILE *fileout;
    char puffer[LENGTH];
    filein=fopen("namein.txt","r");
    fileout=fopen("nameout.txt", "a");

    fgets(puffer,LENGTH,filein);
    strcpy(str2d[0], puffer);

    while(fgets(puffer,LENGTH,filein))
    {

        //SOMEHOW REALLOCATE str2d as of str2d[i+1][255] :)

        strcpy(str2d[i], puffer);
        i++;
    }

    return 0;
}

could you by any chance give me a hint or pseudo code for the realloc part? :/

can I use realloc at all? or do I need a new function in which I write a complete new array and copy paste the old one?

if that's the case, guess it's better to use lists then no? :/

thanks in advance!

Could you use something like this, or are you totally unsure of how many rows the array should have? (can't guess within 5,000 or so?)


It uses very little memory if you make the "count" variable, extra big - it's just a pointer. You can add extra rows up to the "count" you use,
any time you need them - just malloc them, as shown, inside the for loop, below.

Code:

   words=malloc(count * sizeof(char *));
   for(i=0;i<count;i++) {
      words[i]=malloc(LENGTH * sizeof(char));  
   }

I don't know what the problems would be using realloc on a 2D array.

Originally Posted by coffee_cup

ok so I can get realloc work for a 1d array.

but I'm fully confused with 2d arrays...

can I use realloc at all?

Sure you can realloc(). Your array is basically just a 1D array of pointers. So just resize the array as usual. You have to additionally allocate memory for each pointer as soon as you need it.

But in general it's more efficient to start with a reasonable sized array and if you need to resize it then you should use a constant factor (e.g. double it each time). See also Wikipedia: Dynamic array/Geometric expansion and amortized cost

Bye, Andreas