Question

我有一个问题，当我在41 kb文件上使用它时它被压缩（虽然因为它使用行程编码，它似乎总是加倍文件大小）并正确解压缩。但是，当我尝试在一个16,173 kb的文件上使用它并对其进行解压缩时，它没有打开，文件大小为16,171 kb ....所以它解压缩但它没有返回到它＆＃39;原始形式....搞砸了......让我感到困惑，我似乎无法弄清楚我做错了什么......

使用的方法是行程编码，它用计数后跟字节替换每个字节。

在：

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

后：

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

这是我的代码：

    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

您错过了检查字符溢出的运行长度计数，因此如果您的文件中依次包含超过255个相同字符，则会出错。

Answer 2

以下是工作源代码：

    // 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");
    }

C-运行长度编码不适用于大文件，适用于较小的文件

2 个答案: