将包含字符串属性的结构读/写到二进制文件 [英] Read/Write struct containing string property to binary file

问题描述

在读取/写入具有复杂数据(特别是字符串)的结构时遇到问题.我的结构如下所示.

I am running in to an issue while reading/writing a struct having complex data specifically string. my struct looks like below.

struct MyRecord {
  char name[80];
  string location;     // <<== note this 
  double balance;
  unsigned long account_num;
};

我使用不同的功能进行读写.

I use different functions for reading and writing.

这是我用来将数据写入文件的代码

This is the code I am using to write the data to file

struct MyRecord acc;

strcpy(acc.name, "R");
acc.location = "newlocation ok";    // <<== note this 
acc.balance = 1.3;
acc.account_num = 34;

ofstream outbal("balance", ios::out | ios::binary);
outbal.write((char *) &acc, sizeof(struct MyRecord));

就像我使用下面的代码从文件中读取一样.

same like I am using the below code to read from file.

ifstream inbal("balance", ios::in | ios::binary);
inbal.read((char *) &acc, sizeof(struct MyRecord));

当我编译时，它可以很好地编译，但是在执行时，我收到了大量错误消息

when I compile, it compiles nicely, but when executing I am getting the big list of error messages

./binaryfile_3[0x8048f6a]
./binaryfile_3[0x8048e38]
./binaryfile_3[0x8048e54]
/lib/libc.so.6(__libc_start_main+0xe6)[0x148d26]
./binaryfile_3[0x8048aa1]
======= Memory map: ========
00132000-002c3000 r-xp 00000000 fd:00 918500     /lib/libc-2.12.so
// continues....

尽管如此，它可以在以下两个条件下工作.

although, it works in following 2 conditions.

1. 读写功能相同
2. 如果我删除string location

我是C ++的新手，我尝试使用手册进行编写，但最终出现错误.我搜索了几种解决方案，并在添加string属性时都以错误告终.上面的脚本也是我从网站上获取的.我刚刚对其进行了修改，以匹配我的问题，即具有不同功能的具有string

I am new to c++, I tried writing using the manual and ended up in error. I searched through several solution and all end up in error while adding the string property. The above script also I grabbed from a site. I just modified it to match my issue which having different function to read/write and struct having string

请帮助我指出问题所在.谢谢.

Please help me to pin point the issue. Thanks.

推荐答案

添加这两个功能

std::ostream & operator << ( std::ostream & os, const MyRecord & rec ) {
    os.write( rec.name, sizeof( rec.name ) );
    size_t sz = rec.location.size();
    os.write( & sz, iszeof( sz ) );
    os.write( rec.location.c_str(), sz );
    os.write( (char*) & balance, sizeof( rec.balance ) );
    os.write( (char*) & account_num, sizeof( rec.account_num ) );
    return os;
}
std::istream & operator >> ( std::ostream & is, MyRecord & rec ) {
    is.read( rec.name, sizeof( rec.name ) );
    size_t sz;
    is.read( & sz, iszeof( sz ) );
    rec.resize( sz );
    if ( sz != 0 ) {
        is.read( & rec.location[ 0 ], sz );
    }
    is.read( (char*) & balance, sizeof( rec.balance ) );
    is.read( (char*) & account_num, sizeof( rec.account_num ) );
}

这是用法

ofstream outbal("balance", ios::out | ios::binary);
outbal << acc;

ifstream inbal("balance", ios::in | ios::binary);
inbal >> acc;

这是 Boost.Serialization .确实，最好使用boost，而不是我的车辆.

This is poor handmade similarity of Boost.Serialization. Indeed, it would be better to use boost, then my vehicle.

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