c - Reading each line of file into array

Question

I'm reading a file and want to put each line into a string in an array. The length of the file is arbitrary and the length of each line is arbitrary (albeit assume it will be less than 100 characters).

Here's what I've got and it's not compiling. Essentially this is an array to an array of characters, right? So shouldn't it be char** words = (**char)malloc(sizeof(*char));?

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

int main(){


 int BUFSIZE = 32767;//max number of lines to read
 char** words = (**char)malloc(sizeof(*char));//gives error: expected expression before 'char'
 FILE *fp = fopen("coll.txt", "r");
 if (fp == 0){
        fprintf(stderr, "Error opening file");
        exit(1);
 }

int i = 0;
words[i] = malloc(BUFSIZE);
while(fscanf(fp, "%100s", words[i]) == 1)//no line will be longer than 100
{
        i++;
        words[i] = realloc(words, sizeof(char*)*i);
 }

 int j;
 for(j = 0; j < i; j++)
    printf("%s
", words);

 return 0;
}

Note: I've read "Reading from a file and storing in array" but it doesn't answer my question.

Answer 1

There are a few issues with your program. The realloc() statement is not used correctly. I also prefer fgets() for getting a line. Here is my solution. This also uses realloc() to increase the allocation of the buffer lines so that you neither have to know the number of lines in advance nor do you have to read the file in two passes (faster that way). This is a common technique to use when you don't know how much memory you'll have to allocate in advance.

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

int main(void)

    {
    int lines_allocated = 128;
    int max_line_len = 100;

    /* Allocate lines of text */
    char **words = (char **)malloc(sizeof(char*)*lines_allocated);
    if (words==NULL)
        {
        fprintf(stderr,"Out of memory (1).
");
        exit(1);
        }

    FILE *fp = fopen("coll.txt", "r");
    if (fp == NULL)
        {
        fprintf(stderr,"Error opening file.
");
        exit(2);
        }

    int i;
    for (i=0;1;i++)
        {
        int j;

        /* Have we gone over our line allocation? */
        if (i >= lines_allocated)
            {
            int new_size;

            /* Double our allocation and re-allocate */
            new_size = lines_allocated*2;
            words = (char **)realloc(words,sizeof(char*)*new_size);
            if (words==NULL)
                {
                fprintf(stderr,"Out of memory.
");
                exit(3);
                }
            lines_allocated = new_size;
            }
        /* Allocate space for the next line */
        words[i] = malloc(max_line_len);
        if (words[i]==NULL)
            {
            fprintf(stderr,"Out of memory (3).
");
            exit(4);
            }
        if (fgets(words[i],max_line_len-1,fp)==NULL)
            break;

        /* Get rid of CR or LF at end of line */
        for (j=strlen(words[i])-1;j>=0 && (words[i][j]=='
' || words[i][j]=='
');j--)
            ;
        words[i][j+1]='';
        }
    /* Close file */
    fclose(fp);

    int j;
    for(j = 0; j < i; j++)
        printf("%s
", words[j]);

    /* Good practice to free memory */
    for (;i>=0;i--)
        free(words[i]);
    free(words);
    return 0;
    }