.pgr照片文件解析，C++与Java存储数据差别大小端模式[通俗易懂]

1. .pgr是什么？

.pgr文件是二进制的图像文件，可以用普通的文本文件打开，或者查看十六进制的文本信息；

读取需要了解~~~非常重要 ！！！

• 基本数据类型的大小端存储模式
• 表头Header

详细信息可参考：http://www.powergrep.com/manual/PowerGREP.pdf

2. C++与Java存储数据差别——大小端模式

Java是大端模式，C是小端模式；

以int为类，大端模式：高位存高位，低位存地位；
小端模式：高位存地位，地位存高位

• 如 大端：ABCD 小端：DCBA

float，double存储为 符号位，指数位，小数位，更复杂一些；

3. Java读取小端模式数据示例代码

• 可以用BufferTest
• 利用移位方法

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

/************************************* * Class Name: doubleConvert * Description:〈大小端转换〉 * @create 2020/8/19 * @since 1.0.0 ************************************/
public class doubleConvert { 
   

    /** * 向将bytes添加到另一个bytes结尾，并返回位置 * * @param buff 目标数组 * @param pos 目标数组放置的起始位置 * @param lens 添加的长度 * @param dx 要添加的数组 * @return lens添加的长度 */
    public static int addToBuff(byte[] buff, int pos, int lens, byte[] dx) { 
   
        System.arraycopy(dx, 0, buff, pos, lens);
        return lens;
    }

    /** * 获得bytes的一段数据 * * @param buff 原byte数组 * @param startPos 起始位置 * @param lenth 获取的长度 * @return 返回获得的byte数组 */
    public static byte[] getFromBuff(byte[] buff, int startPos, int lenth) { 
   
        byte[] bytes = new byte[lenth];
        System.arraycopy(buff, startPos, bytes, 0, lenth);
        return bytes;
    }

    /** * double转byte数组，小端模式 * * @param d * @return */
    public static byte[] doubleToBytes_Little(double d) { 
   
        long l = Double.doubleToLongBits(d);
        byte b[] = new byte[8];
        b[7] = (byte) (0xff & (l >> 56));
        b[6] = (byte) (0xff & (l >> 48));
        b[5] = (byte) (0xff & (l >> 40));
        b[4] = (byte) (0xff & (l >> 32));
        b[3] = (byte) (0xff & (l >> 24));
        b[2] = (byte) (0xff & (l >> 16));
        b[1] = (byte) (0xff & (l >> 8));
        b[0] = (byte) (0xff & l);
        return b;
    }

    /** * double转byte数组，大端模式 * * @param d * @return */
    public static byte[] doubleToBytes_Big(double d) { 
   
        long l = Double.doubleToLongBits(d);
        byte b[] = new byte[8];
        b[0] = (byte) (0xff & (l >> 56));
        b[1] = (byte) (0xff & (l >> 48));
        b[2] = (byte) (0xff & (l >> 40));
        b[3] = (byte) (0xff & (l >> 32));
        b[4] = (byte) (0xff & (l >> 24));
        b[5] = (byte) (0xff & (l >> 16));
        b[6] = (byte) (0xff & (l >> 8));
        b[7] = (byte) (0xff & l);
        return b;
    }

    /** * byte数组转double * * @param bytes 8位byte数组 * @param littleEndian 是否是小端模式 * @return */
    public static double bytesToDouble(byte[] bytes, boolean littleEndian) { 
   
        ByteBuffer buffer = ByteBuffer.wrap(bytes, 0, 8);
        if (littleEndian) { 
   
            // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN)
            // ByteBuffer 默认为大端(BIG_ENDIAN)模式
            buffer.order(ByteOrder.LITTLE_ENDIAN);
        }
        long l = buffer.getLong();
        return Double.longBitsToDouble(l);
    }

    /** * long转byte数组，小端模式 * * @param l * @return */
    public static byte[] longToBytes_Little(long l) { 
   
        byte b[] = new byte[8];
        b[7] = (byte) (0xff & (l >> 56));
        b[6] = (byte) (0xff & (l >> 48));
        b[5] = (byte) (0xff & (l >> 40));
        b[4] = (byte) (0xff & (l >> 32));
        b[3] = (byte) (0xff & (l >> 24));
        b[2] = (byte) (0xff & (l >> 16));
        b[1] = (byte) (0xff & (l >> 8));
        b[0] = (byte) (0xff & l);
        return b;
    }

    /** * long转byte数组，大端模式 * * @param l * @return */
    public static byte[] longToBytes_Big(long l) { 
   
        byte b[] = new byte[8];
        b[0] = (byte) (0xff & (l >> 56));
        b[1] = (byte) (0xff & (l >> 48));
        b[2] = (byte) (0xff & (l >> 40));
        b[3] = (byte) (0xff & (l >> 32));
        b[4] = (byte) (0xff & (l >> 24));
        b[5] = (byte) (0xff & (l >> 16));
        b[6] = (byte) (0xff & (l >> 8));
        b[7] = (byte) (0xff & l);
        return b;
    }

    /** * byte数组转long * * @param bytes 8位的byte数组 * @param littleEndian 是否是小端模式 * @return * @throws Exception */
    public static long bytesToLong(byte[] bytes, boolean littleEndian) throws Exception { 
   
        if (bytes.length != 8) { 
   
            throw new Exception("参数错误，无法解析。");
        }
        ByteBuffer buffer = ByteBuffer.wrap(bytes, 0, 8);
        if (littleEndian) { 
   
            // ByteBuffer.order(ByteOrder) 方法指定字节序,即大小端模式(BIG_ENDIAN/LITTLE_ENDIAN)
            // ByteBuffer 默认为大端(BIG_ENDIAN)模式
            buffer.order(ByteOrder.LITTLE_ENDIAN);
        }
        return buffer.getLong();
    }

    /** * int转byte数组 ,小端 * * @param num * @return */
    public static byte[] intToBytes_Little(int num) { 
   
        byte[] result = new byte[4];
        result[0] = (byte) ((num >>> 0) & 0xff);
        result[1] = (byte) ((num >>> 8) & 0xff);
        result[2] = (byte) ((num >>> 16) & 0xff);
        result[3] = (byte) ((num >>> 24) & 0xff);
        return result;
    }

    /** * int转byte数组 ,大端 * * @param num * @return */
    public static byte[] intToBytes_Big(int num) { 
   
        byte[] result = new byte[4];
        result[0] = (byte) ((num >>> 24) & 0xff);
        result[1] = (byte) ((num >>> 16) & 0xff);
        result[2] = (byte) ((num >>> 8) & 0xff);
        result[3] = (byte) ((num >>> 0) & 0xff);
        return result;
    }

    /** * byte数组转int,小端 * * @param bytes * @return */
    public static int bytesToInt_Little(byte[] bytes) { 
   
        int result = 0;
        if (bytes.length == 4) { 
   
            int a = (bytes[0] & 0xff) << 0;
            int b = (bytes[1] & 0xff) << 8;
            int c = (bytes[2] & 0xff) << 16;
            int d = (bytes[3] & 0xff) << 24;
            result = a | b | c | d;
        }
        return result;
    }

    /** * byte数组转int,大端 * * @param bytes * @return */
    public static int bytesToInt_Big(byte[] bytes) { 
   
        int result = 0;
        if (bytes.length == 4) { 
   
            int a = (bytes[0] & 0xff) << 24;
            int b = (bytes[1] & 0xff) << 16;
            int c = (bytes[2] & 0xff) << 8;
            int d = (bytes[3] & 0xff) << 0;
            result = a | b | c | d;
        }
        return result;
    }

    /** * byte数组转十六进制 * * @param bytes * @return */
    public static String bytesToHex(byte[] bytes) { 
   
        StringBuilder buf = new StringBuilder(bytes.length * 2);
        for (byte b : bytes) { 
    // 使用String的format方法进行转换
            buf.append(String.format("%02x", new Integer(b & 0xff)));
        }

        return buf.toString();
    }

    /** * 十六进制转byte数组 * * @param str * @return */
    public static byte[] hexToBytes(String str) { 
   
        if (str == null || str.trim().equals("")) { 
   
            return new byte[0];
        }
        byte[] bytes = new byte[str.length() / 2];
        for (int i = 0; i < str.length() / 2; i++) { 
   
            String subStr = str.substring(i * 2, i * 2 + 2);
            bytes[i] = (byte) Integer.parseInt(subStr, 16);
        }
        return bytes;
    }

    public static void main(String[] args) throws Exception { 
   
        int num = 100;
        // 先将int 转小端的byte[], 小端的byte[] 再转回int
        System.out.println("intToLittle: " + bytesToInt_Little(intToBytes_Little(num)));
        // 先将int 转大端的byte[], 大端的byte[] 再转回int
        System.out.println("intToBig: " + bytesToInt_Big(intToBytes_Big(num)));

        long l = 9l;
        System.out.println("longToLittle: " + bytesToLong(longToBytes_Little(l), true));
        System.out.println("longToBig: " + bytesToLong(longToBytes_Big(l), false));

        double d = 9.125d;
        System.out.println("doubleToLittle: " + bytesToDouble(doubleToBytes_Little(d), true));
        System.out.println("doubleToBig: " + bytesToDouble(doubleToBytes_Big(d), false));
        System.out.println("doubleToLittle---Hex: " + bytesToHex(doubleToBytes_Little(d)));
        System.out.println("doubleToBig---Hex: " + bytesToHex(doubleToBytes_Big(d)));
    }
}

4. 效果图

结果如下：

5. 参考

• .pgr照片文件解析，C++与Java存储数据差别大小端模式

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