问题描述

如果我执行以下操作:

ifstream file;
file.open("somefile", ios::binary);

unsigned int data;

file >> data;

我的流将始终设置 failbit 而 data 将保持未初始化状态.但是，如果我改为读取 char 或 unsigned char ，则流很好.perror() 告诉我结果太大".

My stream will always set the failbit and the data will remain uninitialized. However, if I read a char or unsigned char instead, the stream is fine. perror() is telling me "result too large".

我在 Google 上看到的唯一建议是 operator>> 不应该用于二进制数据(首选 read())，但我发现操作符更简洁、更易于使用——而且不需要强制转换所有内容.

The only thing I saw on Google was a suggestion saying that operator>> shouldn't be used for binary data (prefer read()), but I find the operator to be cleaner and easier to use -- and it doesn't require casting everything.

有人能解释一下这个问题吗?

Can someone explain this issue?

推荐答案

iostream 提取运算符 (>>) 尝试解释由空格分隔的数字字符串，而不是二进制数据.有许多不同的方法可以对二进制形式的无符号整数进行编码(例如，32 位 2 的补码表示 在 little-endian 字节顺序).这就是为什么您必须使用 read/write 函数对此类二进制缓冲区进行操作.

The iostream extraction operator (>>) attempts to interpret numerical strings separated by whitespace, not binary data. There are many different ways to encode an unsigned integer in binary form (e.g. a 32-bit 2's complement representation in little-endian byte order). That's why you must use the read/write functions to operate on such binary buffers.

然而，没有什么可以阻止您使用插入和提取运算符实现自己的类，以您希望的任何形式序列化二进制数据.这样的类可能会在内部使用 ifstream 对象的读取函数.或者，boost 序列化库 可能已经包含正是你想要的.

However, nothing prevents you from implementing your own class for serializing binary data in whatever form you wish using the insertion and extraction operators. Such a class would likely use the read function of an ifstream object internally. Alternatively, the boost serialization library may already hold exactly what you want.

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