c - 从txt文件中读取字符，编码并写入二进制文件

Question

我正在编写一个程序，一次从文本文件中读取 4 个字符，将它们打包成一个整数，通过将其向右移动 3 个单位来“加密”该整数，然后将加密的整数写入一个二进制文件。

原始代码:

#include <stdio.h>
#include <limits.h>
#include "encoding.h"

#define KEY 3

int encrypt(int a); 
int pack(char a, char b, char d, char c);

void encoding(char itxt[], char obin[]){ 

        char four[4];

        FILE *inp=fopen(itxt,"r");
        if(!inp){printf("Unable to open %c", inp); return 1;} 

        FILE *outp=fopen(obin,"wb");
        if(!outp){printf("Unable to open %c\n", obin); return 1;} 

        while(fgets(four, 4, inp) != NULL){ 

                int a;

                a = pack(four[0], four[1], four[2], four[3]);
                a = encrypt(a);

                fwrite(&a, sizeof(int), 1, outp);
        }

        printf("Encoding complete!\n");

        fclose(inp);
        fclose(outp);
}

int pack(char a, char  b, char c, char d){ 

        int p = a;

        p = (p<<CHAR_BIT) | b;
        p = (p<<CHAR_BIT) | c;
        p = (p<<CHAR_BIT) | d;

        return p;
}

int encrypt(int a){

        int obin = a>>KEY;

        return obin;
}        

代码可以编译，但不会将任何内容写入二进制文件。任何反馈、提示或技巧将不胜感激。

提前致谢!

*编辑:

#include <stdio.h>
#include <limits.h>
#include "encoding.h"

#define KEY 3

unsigned int encrypt(int a); 
unsigned int pack(char a, char b, char d, char c);

void encoding(char itxt[], char obin[]){ 

        char four[4];

        FILE *inp=fopen(itxt,"r");
        if(!inp){printf("Unable to open %c", inp); return 1;} 

        FILE *outp=fopen(obin,"wb");
        if(!outp){printf("Unable to open %c\n", obin); return 1;} 

        while(fread(&four, sizeof(char), 4, inp) != NULL){ 

                unsigned int a;

                a = pack(four[0], four[1], four[2], four[3]);
                a = encrypt(a);

                fwrite(&a, sizeof(unsigned int), 1, outp);
        }

        printf("Encoding complete!\n");

        fclose(inp);
        fclose(outp);
}

unsigned int pack(char a, char  b, char c, char d){ 

        int p = a;

        p = (p<<CHAR_BIT) | b;
        p = (p<<CHAR_BIT) | c;
        p = (p<<CHAR_BIT) | d;

        return p;
}

 unsigned int encrypt(int a){

        int obin = (a>>KEY) | (a<<(CHAR_BIT*sizeof(a)-KEY)); 

        return obin;
}

Answer 1

编辑后的代码非常接近可操作。这是一个稍微修改过的版本，似乎可以工作。困难在于没有解码函数来检查加密是否可解密。

编码代码enc37.c

#include <stdio.h>
#include <limits.h>

#define KEY 3

unsigned int encrypt(unsigned int a);
unsigned int pack(unsigned char a, unsigned char b, unsigned char d, unsigned char c);
void encoding(const char itxt[], const char obin[]);

void encoding(const char itxt[], const char obin[])
{
    char four[4];

    FILE *inp = fopen(itxt, "r");
    if (!inp)
    {
        fprintf(stderr, "Unable to open %s\n", itxt);
        return;
    }

    FILE *outp = fopen(obin, "wb");
    if (!outp)
    {
        fclose(inp);
        fprintf(stderr, "Unable to open %s\n", obin);
        return;
    }

    while (fread(&four, sizeof(char), 4, inp) == 4)
    {
        unsigned int a;

        a = pack(four[0], four[1], four[2], four[3]);
        a = encrypt(a);

        fwrite(&a, sizeof(unsigned int), 1, outp);
    }

    printf("Encoding complete!\n");

    fclose(inp);
    fclose(outp);
}

unsigned int pack(unsigned char a, unsigned char b, unsigned char c, unsigned char d)
{
    unsigned int p = a;

    p = (p << CHAR_BIT) | b;
    p = (p << CHAR_BIT) | c;
    p = (p << CHAR_BIT) | d;

    return p;
}

unsigned int encrypt(unsigned int a)
{
    unsigned int obin = (a >> KEY) | (a << (CHAR_BIT * sizeof(a) - KEY));

    return obin;
}

int main(int argc, char **argv)
{
    char *i_file = "/dev/stdin";
    char *o_file = "/dev/stdout";

    if (argc == 3)
    {
        i_file = argv[1];
        o_file = argv[2];
    }

    encoding(i_file, o_file);
    return 0;
}

参数列表处理允许您在命令行上指定输入和输出的文件名，但默认为从标准输入读取并写入标准输出。

解码代码dec37.c

#include <stdio.h>
#include <limits.h>

#define KEY 3

typedef unsigned char Byte;
typedef unsigned int  Uint;

Uint decrypt(Uint a);
Uint pack(Byte a, Byte b, Byte d, Byte c);
void unpack(Uint value, Byte *data);
void decoding(const char ibin[], const char otxt[]);

void decoding(const char ibin[], const char otxt[])
{
    FILE *inp = fopen(ibin, "rb");
    if (!inp)
    {
        fprintf(stderr, "Unable to open %s\n", ibin);
        return;
    }

    FILE *outp = fopen(otxt, "w");
    if (!outp)
    {
        fclose(inp);
        fprintf(stderr, "Unable to open %s\n", otxt);
        return;
    }

    Uint value;
    while (fread(&value, sizeof(value), 1, inp) == 1)
    {
        Byte four[4];
        value = decrypt(value);
        unpack(value, four);
        fwrite(four, sizeof(four), 1, outp);
    }

    printf("Decoding complete!\n");

    fclose(inp);
    fclose(outp);
}

void unpack(Uint value, Byte *data)
{
    data[0] = (value >> (3 * CHAR_BIT)) & 0xFF;
    data[1] = (value >> (2 * CHAR_BIT)) & 0xFF;
    data[2] = (value >> (1 * CHAR_BIT)) & 0xFF;
    data[3] = (value >> (0 * CHAR_BIT)) & 0xFF;
}

Uint decrypt(Uint a)
{
    Uint obin = (a << KEY) | (a >> (CHAR_BIT * sizeof(a) - KEY));

    return obin;
}

int main(int argc, char **argv)
{
    char *i_file = "/dev/stdin";
    char *o_file = "/dev/stdout";

    if (argc == 3)
    {
        i_file = argv[1];
        o_file = argv[2];
    }

    decoding(i_file, o_file);
    return 0;
}

测试

如果加密程序是 enc37 并且解密程序是 dec37，那么您可以运行如下命令:

$ ./enc37 enc37.txt enc37.bin
$ ./dec37 enc37.bin dec37.txt
$ diff enc37.txt dec37.txt
$

只要输入文件 (enc37.txt) 的长度是 4 字节的倍数即可。我多次使用 enc37.c 和 dec37.c 作为输入文件。

您还可以以相反的顺序使用解密和加密程序，并且仍然获得往返转换。