c++和java字节高低位的转换

我就是我 2021-05-19 15:25 364阅读 0赞

// 参见java.io.DataInputStream  
    // C++写入的字节顺序是从低到高（左低到右高），  
       而java.io.DataInputStream读取的数据是从高到低（左高到右低)  
    // 所以需要自己改写一下  
    // 功能和java.io.DataInputStream类似的  
    public class CppInputStream extends FilterInputStream {  
      
      public CppInputStream(InputStream in) {  
        super(in);  
      }  
      public final int read(byte b[]) throws IOException {  
        return in.read(b, 0, b.length);  
      }  
      
      public final int read(byte b[], int off, int len) throws IOException {  
        return in.read(b, off, len);  
      }  
      
      public final void readFully(byte b[]) throws IOException {  
        readFully(b, 0, b.length);  
      }  
      
      public final void readFully(byte b[], int off, int len) throws IOException {  
        if (len < 0)  
          throw new IndexOutOfBoundsException();  
        int n = 0;  
        while (n < len) {  
          int count = in.read(b, off + n, len - n);  
          if (count < 0)  
            throw new EOFException();  
          n += count;  
        }  
      }  
      
      public final int skipBytes(int n) throws IOException {  
        int total = 0;  
        int cur = 0;  
        while ((total < n) && ((cur = (int) in.skip(n - total)) > 0)) {  
          total += cur;  
        }  
        return total;  
      }  
      
      public final byte readByte() throws IOException {  
        int ch = in.read();  
        if (ch < 0)  
          throw new EOFException();  
        return (byte) (ch);  
      }  
      
      public final int readUnsignedByte() throws IOException {  
        int ch = in.read();  
        if (ch < 0)  
          throw new EOFException();  
        return ch;  
      }  
      
      public final short readShort() throws IOException {  
        int ch2 = in.read();  
        int ch1 = in.read();  
        if ((ch1 | ch2) < 0)  
          throw new EOFException();  
        return (short) ((ch1 << 8) + (ch2 << 0));  
      }  
      
      public final int readUnsignedShort() throws IOException {  
        int ch2 = in.read();  
        int ch1 = in.read();  
        if ((ch1 | ch2) < 0)  
          throw new EOFException();  
        return (ch1 << 8) + (ch2 << 0);  
      }  
      
      public final char readChar() throws IOException {  
        int ch2 = in.read();  
        int ch1 = in.read();  
        if ((ch1 | ch2) < 0)  
          throw new EOFException();  
        return (char) ((ch1 << 8) + (ch2 << 0));  
      }  
      
      public final int readInt() throws IOException {  
        int ch4 = in.read();  
        int ch3 = in.read();  
        int ch2 = in.read();  
        int ch1 = in.read();  
        if ((ch1 | ch2 | ch3 | ch4) < 0)  
          throw new EOFException();  
        return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));  
      }  
      
      private byte readBuffer[] = new byte[8];  
      
      public final long readLong() throws IOException {  
        readFully(readBuffer, 0, 8);  
        return (((long) readBuffer[7] << 56) + ((long) (readBuffer[6] & 255) << 48)  
            + ((long) (readBuffer[5] & 255) << 40) + ((long) (readBuffer[4] & 255) << 32)  
            + ((long) (readBuffer[3] & 255) << 24) + ((readBuffer[2] & 255) << 16)  
            + ((readBuffer[1] & 255) << 8) + ((readBuffer[0] & 255) << 0));  
      }  
      
      public final float readFloat() throws IOException {  
        return Float.intBitsToFloat(readInt());  
      }  
      
      public final double readDouble() throws IOException {  
        return Double.longBitsToDouble(readLong());  
      }  
    }

简单呀，用Java的字节流，读取一个int的4个字节，然后转换。   
比如读取的数据是：   
byte1 byte2 byte3 byte4   
在其实这是C++的 byte4 byte3 byte2 byte1   
那你可以用位运算转成Java中的对应的整数：   
(byte1& 0xff)<<0  + (byte2& 0xff)<<8 + (byte3& 0xff)<< 16 +(byte4& 0xff)<<24   
这样转换后的，就是Java中的整数了。   
  
  
也可以先用Java读取一个Int进来，然后处理

// Java读取后，顺序已经反了  
    int javaReadInt = ;  
      
    // 将每个字节取出来  
    byte byte4 = (byte) (javaReadInt & 0xff);  
    byte byte3 = (byte) ((javaReadInt & 0xff00) >> 8);  
    byte byte2 = (byte) ((javaReadInt & 0xff0000) >> 16);  
    byte byte1 = (byte) ((javaReadInt & 0xff000000) >> 24);  
      
    // 拼装成 正确的int  
    int realint = (byte1& 0xff)<<0  + (byte2& 0xff)<<8 + (byte3& 0xff)<< 16 +(byte4& 0xff)<<24 ;

另外可以使用ByteBuffer来完成,而不需要自己考虑,如何将字节数组转换为其他数据类型. 使用ByteBuffer,可以设置字节顺序.

ByteBuffer简单的例子 ：

import java.nio.ByteBuffer; 
    import java.nio.ByteOrder; 
    
    public class ByteBufferTest { 
    
      public static void main(String[] args) { 
        //将字节数组转换为int类型 
        byte[] bytes = {0,0,0,1}; 
        ByteBuffer buffer =  ByteBuffer.wrap(bytes); 
        System.out.println(buffer.getInt()); 
       
        ByteBuffer buffer2 = ByteBuffer.wrap(bytes); 
        buffer2.order(ByteOrder.LITTLE_ENDIAN); 
        System.out.println(buffer2.getInt()); 
        
      } 
    
    }