问题
I have a structure, that contain string. Something like that:
struct Chunk {
int a;
string b;
int c;
};
So, i suppose, that i cannot write and read this structure from file using fread and fwrite functions. Because string may reserve different memory capacity. But such code works correctly.
Chunk var;
fwrite(&var, sizeof(Chunk), 1, file);
fread(&var, sizeof(Chunk), 1, file);
Is there really some problems in it?
回答1:
You are justified in doubting this. You should only stream POD types with fwrite and fread and string is not POD.
回答2:
You shouldn't do it like this, because different implementations use different structures of std::string.
In general you should only serialize integral types, the boolean type, binary data (if you can call it serializing). Make sure to use one endian-ness if you are thinking of sharing serialized data between platforms.
Watch out with floats, doubles and pointers. They can become very pesky.
You'll have to watch out with C/C++ structs too ebcause they can contain unpredictable amounts of padding.
回答3:
You should serialize data.
You might like to do this manually - when it comes about std::string , check out:
- const charT* std::string::c_str() const
- const charT* std::string::data() const
When it comes about more complex objects, you might be interested in things like Google Protocol Buffers and/or Thrift.
来源：https://stackoverflow.com/questions/6782632/using-fread-fwrite-for-stl-string-is-it-correct