Question

Trying to work with C I/O currently. I have a file that only holds integers and there is only one per line.. not commas, etc.. what is the best way to read them in:

//WHILE NOT EOF
    // Read a number
    // Add to collection

I am creating 2 files which is working fine.. but ultimately, I want to read them both in, join them into one collection, sort them and then print them out to a new file. There’s no need for you to do all that for me, but please help with the above.. here is my effort so far:

void simpleCopyInputToOutput(void);
void getSortSave(void);

int main()
{
    //simpleCopyInputToOutput();
    getSortSave();

    system("PAUSE");
    return 0;
}

void getSortSave(void)
{
    FILE *fp1;
    FILE *fp2;
    FILE *fpMerged;

    printf("Welcome. You need to input 2 sets of numbers.\n");
    printf("Please input the first sequence. Press 0 to stop.\n");

    if ((fp1 = fopen("C:\\seq1.txt", "w")) == NULL)
    {
        printf("Cannot open or create first file!\n");
        exit(1);
    }

    int num;
    int i = 1;
    while (num != 0)
    {
        printf("Please input value # %d\n", i);
        scanf("%d", &num);

        if (num == 0)
        {
            break;
        }

        fprintf(fp1, "%d\n", num);
        i++;
    }

    printf("Please input the second sequence. Press 0 to stop.\n");
    if ((fp2 = fopen("C:\\seq2.txt", "w")) == NULL)
    {
        printf("Cannot open or create second file!\n");
        exit(1);
    }

    num = -1;
    i = 1;
    while (num != 0)
    {
        printf("Please input value # %d\n", i);
        scanf("%d", &num);

        if (num == 0)
        {
            break;
        }

        fprintf(fp2, "%d\n", num);
        i++;
    }

    fclose(fp1);
    fclose(fp2);

    if ((fp1 = fopen("C:\\seq1.txt", "r")) == NULL)
    {
        printf("Cannot open first file!\n");
        exit(1);
    }

    //WHILE NOT EOF
    // Read a number
    // Add to collection

    //TODO: merge ints from both files, sort and output to new file
}

Answer 1

I would suggest you use fgets:

char buffer[16];
while (fgets(buffer, sizeof(buffer), fp1))
{
    long value = strtol(buffer, NULL, 10);

    /* Use the value... */
}

/* fgets failed ro read, check why */
if (!feof(fp1))
    printf("Error: %s\n", strerror(errno));

Edit: How to get the number of entries in the file: If you don’t keep track of it any other way (like e.g. having the number of items being the first line), the only solution may be to read the file twice. Once to count the number of lines, and once to read the actual numbers. Use fseek or rewind after the counting to “rewind” the read pointer to the beginning of the file.

I would personally put the counting in a separate function, and also the actual reading. This way you don’t have to duplicate code if you want to read from multiple files.