string array of varying length

Question

Im writing a C code to read a file line by line which contains alphabets, CR,LF,'\0'. Below is my attached code sample. I want to store only alphabets from each line to an array such that the numbers of rows in the array equals no of lines in the file and column should be of varying length(depends on the number of character in i-th line).

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

int main()
{
    char *buffer[100];
    char temp[128];
    int c,i=0,j=0;
    int pos=0;
    FILE *file;
    file = fopen("input", "r");
    if (file) {
        while ((c = getc(file)) != EOF){
            if ((c>=65 && c<=90) || (c>=97 && c<=122))
                temp[pos++]=c;
            else if(pos>1) {
                temp[pos]='\0';
                buffer[i]=temp;
                printf ("%s\n",temp);
                i++;
                pos=0;
            }
        }
    }
    fclose(file);
    while (j<i){
        printf("%s\n",buffer[j]);
        j++;
    }
}

If i run my above code, all my buffer[j] contains same string. Can anyone help me out in figuring what was wrong in the code.

A debugger would eagerly step up to the task if you asked it real nice. Apart from that, ask yourself "What am I storing in that pointer array each time I advance to a new string? Is it the same buffer address (temp) over and over?" — WhozCraig
– WhozCraig, Commented Apr 4, 2013 at 12:49

Mike · Accepted Answer · 2013-04-04 12:58:27Z

2

buffer[] is an array of pointers, in your while loop you are pointing each of them to your array temp[]

buffer[i]=temp; // assign the address of temp to buffer[i]

Then you're changing the content of your temp[] array, but the address is always the same.

If you want to store the data from temp into each position in buffer[] you need to allocate memory and copy the data over there. More like:

buffer[i]=malloc(strlen(temp) + 1);
strcpy(buffer[i], temp);

edited Apr 4, 2013 at 12:58

answered Apr 4, 2013 at 12:52

Mike

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3 Comments

WhozCraig Over a year ago

+1 Or buffer[i] = strdup(temp) if you're feeling particularly POSIX-ish that morning =P. Nice answer.

Lundin Over a year ago

@WhozCraig Even if you are feeling POSIX-ish, stick to standard C. There is no reason to ever use strdup anywhere.

WhozCraig Over a year ago

@Lundin I'll keep that in mind. Someone must have some pull, because it wasn't part of the POSIX standard until POSIX.1-2001.

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