C- Run-length encoding doesn't work on large file, worked on smaller file

Question

I have a problem, when I use this on a 41 kb file it compressed (Although because it uses run-length encoding it always seems to double the size of the file) and decompresses properly. However when I tried to use it on a 16,173 kb file and I decompressed it, it didn't open and the file size was 16,171 kb....so it decompressed it but it didn't return back to it's original form....something screwed up....Has me baffled, I just can't seem to figure out what I am doing wrong....

The method used is run-length encoding, it replaces every byte with a count followed by the byte.

Before:

46 6F 6F 20 62 61 72 21 21 21 20 20 20 20 20

After:

01 46 02 6F 01 20 01 62 01 61 01 72 03 21 05 20

Here is my code:

    void compress_file(FILE *fp_in, FILE *fp_out)
    {
        int count, ch, ch2;

        ch = getc(fp_in);
        for (count = 0; ch2 != EOF; count = 0) {
            // if next byte is the same increase count and test again
            do {
                count++;           // set binary count
                ch2 = getc(fp_in); // set next variable for comparison
            } while (ch2 != EOF && ch2 == ch);
            // write bytes into new file
            putc(count, fp_out);
            putc(ch, fp_out);
            ch = ch2;
        }
        fclose(fp_in);
        fclose(fp_out);
        fprintf(stderr, "File Compressed\n");
    }

    void uncompress_file(FILE *fp_in, FILE *fp_out)
    {
        int count, ch, ch2;

        for (count = 0; ch2 != EOF; count = 0) {
            ch = getc(fp_in);   // grab first byte
            ch2 = getc(fp_in);  // grab second byte
            // write the bytes
            do {
                putc(ch2, fp_out);
                count++;
            } while (count < ch);
        }
        fclose(fp_in);
        fclose(fp_out);
        fprintf(stderr, "File Decompressed\n");
    }

Answer 1

Here is the working source code:

    // Chapter 22 Programming Project #7

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

    void compress_file(FILE *fp_in, FILE *fp_out);
    void uncompress_file(FILE *fp_in, FILE *fp_out);

    int main(void)
    {
        FILE *fp_in, *fp_out;
        char nm_in[FILENAME_MAX], nm_out[FILENAME_MAX];
        int chk;

        for (;;) {
            printf(" ----------------------------------------- \n");
            printf("|             1 - Compress                |\n");
            printf("|             2 - Decompress              |\n");
            printf("|             3 - Exit                    |\n");
            printf(" ----------------------------------------- \n");
            do {
                printf("Enter a command: ");
                scanf(" %d", &chk);
            } while (isalpha(chk));

            if (chk == 3)
                exit(EXIT_SUCCESS);

            printf("Enter input file name: ");
            scanf(" %s", nm_in);
            printf("Enter output file name: ");
            scanf(" %s", nm_out);
            // Open file to read from
            while ((fp_in = fopen(nm_in, "rb")) == NULL) {
                fprintf(stderr, "Can't open \"%s\"\n", nm_in);
                printf("Enter input file name: ");
                scanf(" %s", nm_in);
            }
            // Open file to write to
            while ((fp_out = fopen(nm_out, "wb")) == NULL) {
                fprintf(stderr, "Can't create \"%s\"\n", nm_out);
                printf("Enter output file name: ");
                scanf(" %s", nm_out);
            }
            switch(chk) {
                case 1: compress_file(fp_in, fp_out); break;
                case 2: uncompress_file(fp_in, fp_out); break;
            }
            putchar('\n');
        }

        return 0;
    }

    void compress_file(FILE *fp_in, FILE *fp_out)
    {
        int count, ch, ch2, chk;

        ch = getc(fp_in);
        ch2 = ch;
        while (ch2 != EOF) {
            // if next byte is the same increase count and test
            for (count = 0; ch2 == ch && count < 255; count++) {
                ch2 = getc(fp_in); // set next variable for comparison
            }
            // write bytes into new file
            putc(count, fp_out);
            putc(ch, fp_out);
            ch = ch2;
        }
        fclose(fp_in);
        fclose(fp_out);
        fprintf(stderr, "File Compressed\n");
    }

    void uncompress_file(FILE *fp_in, FILE *fp_out)
    {
        int count, ch, ch2;

        for (count = 0; ch2 != EOF; count = 0) {
            ch = getc(fp_in);   // grab first byte
            ch2 = getc(fp_in);  // grab second byte
            // write the bytes
            do {
                putc(ch2, fp_out);
                count++;
            } while (count < ch);
        }
        fclose(fp_in);
        fclose(fp_out);
        fprintf(stderr, "File Decompressed\n");
    }

Answer 2

You miss to check your run length count for char overflow, so this will go wrong if you have more than 255 identical characters in your file in sequence.