C 语言的 hexdump 程序

Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 255

void hexDump (char *desc, void *addr, int len) {
    int i;
    unsigned char buffLine[17];
    unsigned char *pc = (unsigned char*)addr;


    if (desc != NULL){

       printf ("%s:\n", desc);

    }


    for (i = 0; i < len; i++) {


        if ((i % 16) == 0) {

            if (i != 0)

                printf ("  %s\n", buffLine);
           // if (buffLine[i]== '\0') break;

            if (pc[i] == 0x00) exit(0);

            // Prints the ADDRESS
            printf ("  %07x ", i);
        }

        // Prints the HEXCODES that represent each chars.
        printf ("%02x", pc[i]);
        if ((i % 2) == 1) 
            printf (" "); 



        if ((pc[i] < 0x20) || (pc[i] > 0x7e)){
            buffLine[i % 16] = '.';
        }

        else{

           buffLine[i % 16] = pc[i];

        }    


        buffLine[(i % 16) + 1] = '\0'; //Clears the next array buffLine


    }



    while ((i % 16) != 0) {
        printf ("   ");
        i++;
    }


    printf ("  %s\n", buffLine);
}

//----------------------------------------------

int main()
    {
            FILE *ptr_file;
            char buff[SIZE];

            ptr_file =fopen("input.txt","r");
            if (!ptr_file){
            printf("returning 1");
                return 1;
            }

            memset(buff, '\0', sizeof( buff) );
            fgets(buff,SIZE, ptr_file);
            hexDump ("buff", &buff, sizeof (buff));

        fclose(ptr_file);

            return 0;
    }
    //*/

Sorry, this I'm new to C, so it's kinda of messy right now, I been deleting parts and making temporary codes, etc... So anyways this works by reading characters from input.txt and outputs it by printing the hexidecimal representation and the Acii representations on the right. For bytes forming non-printable characters, print a '.' character (a dot/period character, ie hex value 2E).:

0003540: 0504 0675 6e73 6967 6e65 6420 6368 6172 ...unsigned char
0003550: 0008 0107 0000 0131 0675 6e73 6967 6e65 .......1.unsigne

BUT my program does not print anything beyond the 'new line' in the text. For example: in my input.txt, I have:

This is line 1 so this will be longer than usual
line 2 is this
this is the last line

after reading my program, it only outputs like this:

  0000000 5468 6973 2069 7320 6c69 6e65 2031 2073   This is line 1 s
  0000010 6f20 7468 6973 2077 696c 6c20 6265 206c   o this will be l
  0000020 6f6e 6765 7220 7468 616e 2075 7375 616c   onger than usual
  0000030 0a00 0000 0000 0000 0000 0000 0000 0000   ................

But for some reason it won't print and hex the second, third line....

Answer 1

You call fgets only once. fgets reads a line from the file and stops when it exhausts the SIZE char limit, when it hits the end of the file or when it encounters a newline character. So that behaviour is to be expected.

The length of the data will usually be less than the char limit, but you print all SIZE chars, which gives you the zeros.

If you want to treat all lines, you should cal fgets in a loop and break it when it returns NULL . You should also pass strlen(buf) as length parameter instead of sizeof(buf) , which will give you the usually overlong SIZE .

The purpose of a hex dumper is to make the data of any file visible. You use fgets and char , which should be used for text files. (I'm not sure what fgets does when it encounters a null byte, for example.)

It is therefore better to use bytes, ie an unsigned char and read them block-wise with fread . If you make the block-size a multiple of 16, this will help you to format your output. So:

for (;;) {
    unsigned char buf[SIZE];
    size_t n = fread(buf, 1, SIZE, f);

    if (n > 0) dump(buf, n);
    if (n < SIZE) break;
}

Answer 2

You need to open the file in binary mode using "rb" not "r"

Then use fread() to read from the file, either by reading chunks from it or by reading the whole file.

Answer 3

You should use fread() to read the file, and put that in a loop (until it returns 0), so that it reads the whole file. If you are on Windows also make sure to open the file with "rb" (binary mode), while on Unix it shouldn't matter.

One last suggestion would be to use isascii() or one of its sister functions, instead of manually checking for "printability". See http://linux.die.net/man/3/isalnum .

Answer 4

I'm doing the same problem but for both binary dump & hexdump. However, for the last line of output, it isn't in the right place. Please help. Thank you!

Answer 5

void HexDump(const void* data, size_t size) 
{
    char ascii[17];
    size_t i, j;
    ascii[16] = '\0';
    for (i = 0; i < size; ++i) {
        printf("%02X ", ((unsigned char*)data)[i]);
        if (((unsigned char*)data)[i] >= ' ' && ((unsigned char*)data)[i] <= '~') {
            ascii[i % 16] = ((unsigned char*)data)[i];
        } else {
            ascii[i % 16] = '.';
        }
        if ((i+1) % 8 == 0 || i+1 == size) {
            printf(" ");
            if ((i+1) % 16 == 0) {
                printf("|  %s \n", ascii);
            } else if (i+1 == size) {
                ascii[(i+1) % 16] = '\0';
                if ((i+1) % 16 <= 8) {
                    printf(" ");
                }
                for (j = (i+1) % 16; j < 16; ++j) {
                    printf("   ");
                }
                printf("|  %s \n", ascii);
            }
        }
    }
}

You need to give the input as a buffer address and the size of the buffer, You can see the output like below

01 0F 30 36  20 32 35 33  32 20 34 34  31 33 20 31    ..06.2532.4413.1
37 02 05 01  A0 58 6A 59  06 01 00 30  08 10 00 00    7....XjY...0....
02 7C AB B6  67                                      .|..g