使用 fwrite 转储的文件是否可以跨不同系统移植？

发布于 2024-08-20 07:07:35 字数 429 浏览 14 评论 0原文

我可以假设使用 fwrite 生成并使用 fread 读取的文件可以跨不同系统移植吗？ 32 位/64 位 Windows、OSX、Linux。

//dumping
FILE *of =fopen("dumped.bin","w");
double *var=new double[10];
fwrite(var, sizeof(double), 10,FILE);
//reading
file *fo=fopen()
double *var=new double[10];
fread(var,sizeof(double),10,of);

那么结构体呢

struct mat_t{
    size_t x;
    size_t y;
    double **matrix;
}

？它们是可移植的吗？

原文

Can I assume a file generated with fwrite and read using fread is portable across different systems. 32bit/64bit windows,osx,linux.

//dumping
FILE *of =fopen("dumped.bin","w");
double *var=new double[10];
fwrite(var, sizeof(double), 10,FILE);
//reading
file *fo=fopen()
double *var=new double[10];
fread(var,sizeof(double),10,of);

And what about structs

struct mat_t{
    size_t x;
    size_t y;
    double **matrix;
}

Are these portable?

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囚我心虐我身 2024-08-27 07:07:35

简短回答：否

详细回答：

您正在写出数据的二进制表示形式。
这不能跨平台、操作系统甚至编译器移植。

您编写的所有对象都有可以更改的内容：

int:        size and endianess.
double:     size and representation.
structure:  Each member has to be looked at individually.
            The structure itself may be padded different on different compilers.
            Or even the same compiler with different flags.
pointers:   Are meaningless even across processes on the same machine.
            All pointers have to be converted into something meaningful like
            a named object that is provided separately. The transport will then
            have to convert named objects into pointers at the transport layer
            at the destination.

您有两个主要选项：

流式传输数据。
这基本上是将结构转换为文本表示并发送字符串。对于小型对象，API 结构这是当前进行跨平台/语言通信的标准方法（尽管数据通常以 XML 或 Json 等格式包装）。
转换为网络中立的二进制格式
为此，我们有 htonl() 和函数族() 用于转换整数。双精度数更难，通常转换为两个整数（值取决于精度要求）。字符串被转换为长度，后跟字符序列等。然后每个字符串被单独写入流。这可以比流式传输更紧凑（因此更高效）。不利的一面是，您将两端紧密耦合到一种非常特定的格式，从而使解决方案特别脆弱，并且在错误情况下更难纠正。

Short Answer: NO

Long Answer:

You are writing out the binary representation of the data.
This is not portable across platforms or OS or even compilers.

All the objects you have written have things that can change:

int:        size and endianess.
double:     size and representation.
structure:  Each member has to be looked at individually.
            The structure itself may be padded different on different compilers.
            Or even the same compiler with different flags.
pointers:   Are meaningless even across processes on the same machine.
            All pointers have to be converted into something meaningful like
            a named object that is provided separately. The transport will then
            have to convert named objects into pointers at the transport layer
            at the destination.

You have two main options:

Streaming the data.
This is basically converting the structure into a textual representation and sending the string. For small object, API structures this is current standard method of doing cross platform/language communication (though the data is usually wrapped in some format like XML or Json).
Convert to a network neutral binary format
For this we have htonl() and family of functions() for converting integers. Doubles are harder and usually converted into two integers (the values depend on accuracy requirements). Strings are converted to a length followed by a sequence of characters etc. Then each is written individually to the stream. This can be much more compact than streaming (and thus efficient). The down side is that you are tightly coupling both ends to a very specific format and thus makes the solution particularly brittle and harder to correct in error situations.

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对你再特殊 2024-08-27 07:07:35

fwrite 和 fread 具有很强的可移植性，但是您可能会遇到诸如 sizeof(double) 之类的问题，这些问题可能因系统而异。确保您编写的每个二进制字段都有一个定义的大小，该大小不依赖于编译器或操作系统 - 您可以通过使用显式给出其大小的类型（例如uint32_t）来很大程度上实现这一点。

您还必须担心字节顺序，但是您可以使用宏 ntoh、ntohl、hton 和 htonl可以用来为您交换字节顺序，并且它们应该被定义为可以在您编译它们的任何系统上正常工作。