复杂数据的文件读写问题

lemoncookie

原帖由 prc 于 2008-10-9 18:50 发表

这个说法有根据吗？

不明白，我只知道fread/fwrite是Ｃ标准库中的函数，语义也很清楚，支持标准库函数的系统应该都能用

雨过白鹭洲

A fundamental problem with binary I/O is that it can be used to read only data that has been written on the same system. This was OK many years ago, when all the UNIX systems were PDP-11s, but the norm today is to have heterogeneous systems connected together with networks. It is common to want to write data on one system and process it on another. These two functions won't work, for two reasons.

1. The offset of a member within a structure can differ between compilers and systems, because of different alignment requirements. Indeed, some compilers have an option allowing structures to be packed tightly, to save space with a possible runtime performance penalty, or aligned accurately, to optimize runtime access of each member. This means that even on a single system, the binary layout of a structure can differ, depending on compiler options.

2. The binary formats used to store multibyte integers and floating-point values differ among machine architectures.

We'll touch on some of these issues when we discuss sockets in Chapter 16. The real solution for exchanging binary data among different systems is to use a higher-level protocol. Refer to Section 8.2 of Rago [1993] or Section 5.18 of Stevens, Fenner, & Rudoff [2004] for a description of some techniques various network protocols use to exchange binary data.

From APUE Chapter 5 Standard I/O Library

一般来说，这不是一个问题，因为我们只是在同一台机器上写入，以后再读取出来。。。

qwjcool

我的做法是这样地
对于包含别struct的struct，老老实实一个个字段写
对于不包含其它struct的struct，就直接整个输出

struct b
{
  int var;
};

struct a
{
  int var;
  struct b* s;
};

struct b sb;
struct a sa;
sa.s=&sb;

//write
fopen("filename","wb");
fwrite( &(sa.var), sizeof(int), 1, fd);
fwrite( sa.s, sizeof(struct b), 1, fd);
fclose(fd);

//read
fopen("filename","rb");
fread( &(sa.var), sizeof(int), 1, fd);
fread( sa.s, sizeof(struct b), 1, fd);
fclose(fd);

供楼主参考。。。