c - 未检测到 EOF

Question

我希望这不是一个问题。我检测 EOF 的条件似乎不起作用。代码继续通过 EOF 并在语句中处理。当我重新创建文本时，它看起来很合适，但是整个带有垃圾代码的 bmp 也打印出来告诉我文本标志的结尾从未被编码。我在下一个 else 条件中放置了一个 printf 语句，但它从未输入要打印的语句。我看不出问题是什么，如果它就在我面前，或者更不祥的东西。一如既往的感谢!

/*******************************************************************************
 * This code is to take a text document and using steganography techniques, hide
 * the text within a bmp. It will take each character of the text, parse it into
 * four 2 bit pieces and inject those bits into the two least significant bits
 * of each pixel color (BGR) byte as well as the line padding.
 ******************************************************************************/
#include <stdio.h>

/*******************************************************************************
 * getIntFromArray (borrowed from class notes). Takes unsigned character array
 * and assembles/returns an int value using bit shifting with OR.
 ******************************************************************************/
int getIntFromArray(unsigned char bytes[])
{
  int n =
          bytes[0] |
          bytes[1] << 8 |
          bytes[2] << 16 |
          bytes[3] << 24;
  return n;
}

/*******************************************************************************
 * bitWise. Take unsigned char pointer and character, parses the character
 * using bitwise manipulation and injects 2 bits into the 2 least significant
 * bits of each pixel color byte as well as padding.
 ******************************************************************************/
void bitWise(unsigned char* bytes, char character)
{
  int i;
  char tmpChar;
  for(i = 0; i < 4; ++i)
  {
    tmpChar = character;
    tmpChar &= 3;
    bytes[i] &= 252;
    bytes[i] |= tmpChar;
    character = character >> 2;
  }
}

int flag = 0;

int main(int argc, char **argv)
{
  char *infilename = argv[1];
  char *outfilename = argv[2];

  unsigned char header[54];

  FILE *in = fopen(infilename, "rb");/*Command line input.*/
  FILE *out = fopen(outfilename, "wb");/*Command line input.*/

  int pixelWidth;
  int pixelHeight;
  int i;
  int j;

  fread(header, 1, 54, in);/* read header into array */

  pixelWidth = getIntFromArray(&header[18]);
  pixelHeight = getIntFromArray(&header[22]);

  fwrite(header, 1, sizeof(header), out);/* write header to output file */

  for(i = 0; i < pixelHeight; ++i)/*Loop to read pixel data from bmp.*/
  {
    for(j = 0; j < pixelWidth; ++j)
    {
      unsigned char bytes[4];
      unsigned char character = 0;

      fread(&bytes, 1, 4, in);/*Reads sequentially pixel and padding bytes.*/
      if(flag == 0)/*Breakout flag, initially set to 0.*/
      {
        character = getchar();/*Takes in characters from stdin.*/
        if(character != EOF)/*Breakout if EOF.*/
        {
          bitWise(bytes, character);
        }
        else
        {
          bitWise(bytes, 0);/*Sets end of hidden text with 4 bytes LSB to 0.*/
          flag = 1;
        }
      }
      fwrite(&bytes, 1, 4, out);
    }
  }
  fclose(in);
  fclose(out);
  return 0;
}

Answer 1

您正在将 signed int 分配给 unsigned int。结果将不是您期望的那样。它将是一个所有位都设置为 1 的值。 (EOF 的值为 -1，因此已签名)。

长话短说，它应该是 int。简单的 int character 就可以达到目的。

另外 getchar() 返回 int。int getchar(void);

还有一些其他事情要做:-

• fread 应检查返回值。

  size_t fread(void * restrict ptr,size_t size, size_t nmemb,FILE * restrict stream);

The fread function returns the number of elements successfully read, which may be less than nmemb if a read error or end-of-file is encountered. If size or nmemb is zero, fread returns zero and the contents of the array and the state of the stream remain unchanged

• 另一件事是检查fopen() 的返回值。如果失败，返回值将为 NULL。