在读取文本文件之前为2D字符串数组分配空间

Question

I'm reading from a large text file which contains a string followed by a newline. I'm using fgets to read each string and store them in a 2D string array as well as malloc to assign memory.

void read_file (char **dictionary, char * argv[])

{

FILE * file_name;
int i = 0, word_count = 0, c;

    file_name = fopen(argv[0], "r");
    if (file_name == NULL)
        {
            printf("Cannot open file");
        }
    while (fgets(dictionary[i], MAX_WORD_LENGTH, file_name))
        {
            dictionary[i][strlen(dictionary[i]) - 1] = '\0';
            word_count++;
            i++;
        }
    printf("\n%d words scanned in from: %s\n", word_count, argv[0]);
    fclose(file_name);
}

char ** AllocateDictionaryMemory (void)

{

int i;

char **p = malloc(MAX_WORDS * sizeof(*p));

        for (i = 0; i < MAX_WORDS; i++)
        {
            p[i] = malloc(MAX_WORD_LENGTH + 1);
        }
        if (p == NULL)
        {
            printf("Failed to allocate 2D string array space\n.");
        }

return p;

This uses a fixed value of MAX_WORD_LENGTH (10). However I'm now wanting to do it with with a non-fixed sized of words which is decided by finding the longest word in the text file it is given. I have a function to find the longest word in the dictionary as well. The problem is the malloc function needs max word length given to it, and the read_file function needs a dictionary array to read into - both of which happen before I can run the find longest word function.

I guess the question is - how can I find the longest word in the text file before I malloc space for the dictionary, and before the actual text file is read into the dictionary.

I know I could just set max_word_length to be something ridiculously huge but that kind of defeats the point - I want the size of the space to be decided once it has found the max word length.

read file --> find longest word --> malloc space big enough for the longest word --> read file into new space is the aim.

Answer 1

The following function goes through the file to count the length of all words and returns the length of the longest word.

int findLongestWord(FILE *fin)
{
    int c, i=0, longest= 0
    while ((c=fgetc(fin))!=EOF)
    {
        if (isspace(c)) {
            if (i>longest) longest= i;
            i= 0;
        }
        else i++;
    }
    if (i>longest) longest= i;    // suppose last word was longest..
    return longest;
}

Don't forget to rewind the file before processing it again.

Answer 2

The file can be read and memory allocated at the same time. This allocates each pointer but could be modified to allocate a block of pointers for efficiency. Each pointer has just enough memory allocated for the length of the input.

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

char** readwords( FILE *pf, int *wordcount);

int main( int argc, char *argv[])
{
    FILE *wordfile = NULL;
    char **s = NULL;
    int wordsize = 0;
    int each = 0;

    if ( argc < 2)
    {
        printf ( "program needs a filename as in:\nprogram filename\n");
        return 1;
    }

    if ( ( wordfile = fopen(argv[1], "r")) == NULL)
    {
        printf("Cannot open file");
        return 2;
    }

    s = readwords( wordfile, &wordsize);
    fclose ( wordfile);

    if ( s == NULL)
    {
        printf ( "no words in array\n");
        return 0;
    }

    for ( each = 0; each < wordsize; each++)
    {
        printf ( "%s\n", s[each]);
    }

    while ( wordsize) {
        wordsize--;
        free ( s[wordsize]);
    }
    free ( s);

    return 0;
}

char** readwords( FILE *pf, int *count)
{
    char** words = NULL;//NULL so realloc will work on the first call
    char** temp = NULL;
    char input[200] = "";

    //read each line into fixed size array
    while ( fgets ( input, sizeof ( input), pf))
    {
        //remove trailing newline if present
        input[strcspn ( input, "\n")] = '\0';
        //increment count of words
        *count = *count + 1;
        //allocate another pointer
        if ( ( temp = realloc ( words, *count * sizeof ( char *))) == NULL)
        {
            //if realloc fails 'words' should still be valid
            printf ( "realloc failed\n");
            *count = *count - 1;
            return words;
        }
        words = temp;//assign temp back to words
        //allocate memory to the pointer
        if ( ( words[*count - 1] = malloc ( strlen ( input) + 1)) == NULL)
        {
            printf ( "malloc failed\n");
            *count = *count - 1;
            return words;
        }
        strcpy ( words[*count - 1], input);
    }
    return words;
}