从十六进制文件读取的 C 程序给出意外的输出

Question

为什么这个程序不能正确读取十六进制文件？

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

char *buffer;
unsigned int fileLen;
void ReadFile(char *name);


void ReadFile(char *name)
{
        FILE *file;

        file = fopen(name, "rb");
        if (!file)
        {
                fprintf(stderr, "Unable to open file %s", name);
                return;
        }

        //Getting file length
        fseek(file, 0, SEEK_END);
        fileLen=ftell(file);
        fseek(file, 0, SEEK_SET);

        //Allocating memory
        buffer=(char *)malloc(fileLen+1);
        if (!buffer)
        {
                fprintf(stderr, "Mem error!");
                                fclose(file);
                return;
        }

        fread(buffer, fileLen, 1, file);
        fclose(file);


}

int main()
{
   var32 code;
   char filename[20];
   printf("Enter the file name: ");
   scanf("%s", &filename);
   ReadFile(filename);
   printf("FIle contents: %x\n",buffer);

}

如果我打印一个巨大的十六进制文件，它只会打印 5 到 6 位数字。

Answer 1

printf("FIle contents: %x\n",buffer);

“%x”仅打印一个十六进制值。它正在打印缓冲区的内存地址，而不是其内容。

尝试改变:

    fread(buffer, fileLen, 1, file);
    fclose(file);

之后添加:

    ...
    fclose(file);
    size_t i;
    for (i = 0; i < fileLen; i++)
        printf("%02x ", buffer[i];

这将打印整个二进制内容。但没有必要读取整个文件来执行此操作，您可以一次输出 1 K 的 block ...

不同的实现

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#define BUFFER_SIZE     4096
int main(void)
{
     uint8_t  *buffer;  // Explicit 8 bit unsigned, but should equal "unsigned char"
     FILE     *file;
     char     filename[512];
     // We could also have used buffer[BUFFER_SIZE], but this shows memory alloc
     if (NULL == (buffer = malloc(BUFFER_SIZE)))
     {
          fprintf(stderr, "out of memory\n");
          return -1;
     }
     printf("Enter the file name: ");
     // Read a line terminated by LF. Max filename size is MAXPATH, or 512
     fgets(filename, 512, stdin);
     // Trim filename (Windows: CHECK we don't get \r instead of \n!)
     {
         // Being inside a { }, crlf won't be visible outside, which is good.
         char     *crlf;
         if (NULL != (crlf = strchr(filename, '\n')))
              *crlf = 0x0;
     }
     if (NULL == (file = fopen(filename, "rb")))
     {
         fprintf(stderr, "File not found: '%s'\n", filename);
         return -1;
     }
     while(!feof(file) && !ferror(file))
     {
          size_t i, n;
          if (0 == (n = (size_t)fread(buffer, sizeof(uint8_t), BUFFER_SIZE, file)))
               if (ferror(file))
                    fprintf(stderr, "Error reading from %s\n", filename);
                    // Here, n = 0, so we don't need to break: next i-cycle won't run
          for (i = 0; i < n; i++)
          {
               printf("%02x ", buffer[i]);
               if (15 == (i % 16))
                    printf("\n"); // Every 16th byte, a newline
          }
     }
     fclose(file); // file = NULL; // This ensures file won't be useable after fclose
     free(buffer); // buffer = NULL; // This ensures buffer won't be useable after free
     printf("\n");
     return 0;
}