Question

Hey guys, I’m currently trying to implement a function using C that takes in two file names as command line arguments and compare them lexicographically.

The function will return -1 if the contents of the first file are less than the contents of the second file, 1 if the contents of the second file are less than the contents of the first file, and 0 if the files are identical.

Please give me some advice on how I should start with this.

[EDIT]

Hey guys sorry if there’s any unclear part in the question, so I’ll just post the link to the question here: Original question. Thing is it’s an uni assignment so we’re expected to do it using only basic C properties, probably only including stdio.h, stdlib.h, and string.h. Sorry for the trouble caused. Also here’s the code I already have, my main problem now is that the function doesn’t know that file1.txt (refer to the link) has it’s first line longer than file2.txt, but is actually lexicographically less:

int filecmp(char firstFile[], char secondFile[])
{
    int similarity = 0;
    FILE *file1 = fopen(firstFile, "r");
    FILE *file2 = fopen(secondFile, "r");
    char line1[BUFSIZ];
    char line2[BUFSIZ];

    while (similarity == 0)
    {
        if (fgets(line1, sizeof line1, file1) != NULL)
        {
            if (fgets(line2, sizeof line2, file2) != NULL)
            {
                int length;

                if (strlen(line1) > strlen(line2))
                {
                    length = strlen(line1);
                }
                else
                {
                    length = strlen(line2);
                }

                for (int i = 0; i < length; i++)
                {
                    if (line1[i] < line2[i]) similarity = -1;
                    if (line1[i] > line2[i]) similarity = 1;
                }
            }
            else
            {
                similarity = 1; //As file2 is empty
            }
        }
        else
        {
            if (fgets(line2, sizeof line2, file2) != NULL)
            {
                similarity = -1; // As file1 is empty
            }
            else break;
        }
    }

    fclose(file1);
    fclose(file2);

    return similarity;
}

[END EDIT]

Many thanks,
Jonathan Chua

Answer 1

Are you allowed to use strcmp?

If so (untested):

int ret = 0;
while (ret == 0)
{ 
    char line1 [ MAX_LINE_LEN ]; 
    char line2 [ MAX_LINE_LEN ]; 
    if (fgets(line1, MAX_LINE_LEN, file1) != NULL )
    {
        if (fgets(line2, MAX_LINE_LEN, file2) != NULL )
        {
            ret = strcmp(line1, line2);
        }
        else
        {
            ret = 1;
        }
    }
    else
    {
        if (fgets(line2, MAX_LINE_LEN, file2) != NULL )
        {
            ret = -1;
        }
        else
        {
            break;
        }
    }
}
return ret;