问题描述

我使用以下 matlab 代码创建了一个二进制文件:

I have created a binary file using the following matlab code:

x is an array of int32 numbers
n is the length of x

fid = fopen("binary_file.dat", "wb");
fwrite(fid, n, 'int32');
fwrite(fid, x, 'int32');
fclose(fid);

我可以使用下面的 C 代码来读取这个文件:

I can use the following C code to read this file:

fp = fopen("binary_file.dat", "rb");
int n;
fread(&n, 4, 1, fp);//read 4 bytes
int *x = new int[n];
for (int i = 0; i < n; i++)
{
int t;
fread(&t,4, 1,fp);//read 4 bytes
x[i] = t;
}
......

上面的 C 代码可以读取正确的结果.但是，我现在想用 JAVA 读取这样的二进制文件.我的代码如下所示:

The above C code can read correct results. However, I now want to read such binary file in JAVA. My code is shown as follows:

DataInputStream data_in = new DataInputStream(
             new BufferedInputStream(
                    new FileInputStream(
                new File("binary_file.dat"))));
while(true)
{
   try {
      int t = data_in.readInt();//read 4 bytes
      System.out.println(t);
   } catch (EOFException eof) {
    break;
   }
}
data_in.close();

它确实在 n+1 次循环后终止，但结果不正确.谁能帮帮我.非常感谢！

It DOES terminates after n+1 loops, but the results are not correct. Can anybody help me out. Thanks very much!

推荐答案

我猜这是字节序问题，即你的二进制文件写成小端整数(可能是因为您使用的是 Intel 或类似的 CPU).

As I was guessing it is an endianness issue, i.e. your binary file is written as little-endian integers (probably, because you are using a Intel or similar CPU).

然而，Java 代码正在读取大端整数，无论它在什么 CPU 上运行.

The Java code, however, is reading big-endian integers, no matter what CPU it is running on.

为了显示问题，以下代码将读取您的数据并将整数显示为字节序转换前后的十六进制数.

To show the problem the following code will read your data and display the integers as hex number before and after endianness conversion.

import java.io.*;

class TestBinaryFileReading {

  static public void main(String[] args) throws IOException {  
    DataInputStream data_in = new DataInputStream(
        new BufferedInputStream(
            new FileInputStream(new File("binary_file.dat"))));
    while(true) {
      try {
        int t = data_in.readInt();//read 4 bytes

        System.out.printf("%08X ",t); 

        // change endianness "manually":
        t = (0x000000ff & (t>>24)) | 
            (0x0000ff00 & (t>> 8)) | 
            (0x00ff0000 & (t<< 8)) | 
            (0xff000000 & (t<<24));
        System.out.printf("%08X",t); 
        System.out.println();
      } 
      catch (java.io.EOFException eof) {
        break;
      }
    } 
    data_in.close();
  }
}

如果您不想手动"更改字节顺序，请参阅此问题的答案问题:
将小端文件转换为大端

If you don't want to do change endianness "manually", see answers to this question:
convert little Endian file into big Endian

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