使用seekg读取二进制数据失败

我以以下方式写入数据:

long RecordIO::writeRecord(Data *record)
{
    this->openWrite();

    fstream::pos_type offset = file->tellp();
    file->write(reinterpret_cast<char*>(record), sizeof(Data));
    return (long)offset;
}

将存储返回的偏移量,并在以后检索。数据是包含数据的结构。

稍后,我尝试使用以下代码再次读取相同的数据:

Data* RecordIO::getRecord(long offset)
{
    openRead();
    file->seekg((fstream::pos_type) offset);
    Data data;
    file->read(reinterpret_cast<char *>(&data), sizeof(Data));
    return new Data(data);
}

sizeof(Data)返回768。我得到的偏移量是768和1536。但是当我检查数据的内容时,我会完全胡言乱语。我做错什么了吗? 编辑:

struct Data{
  long key;
  char postcode[8];
  char info1[251];
  char info2[251];
  char info3[251];
};

我就是这样填的:

for(int i = 1; i <= numOfRecords; ++i){
    newData.key = i;

    newData.postcode[0] = '1' + (rand() % 8);
    newData.postcode[1] = '0' + (rand() % 9);
    newData.postcode[2] = '0' + (rand() % 9);
    newData.postcode[3] = '0' + (rand() % 9);
    newData.postcode[4] = ' ';
    newData.postcode[5] = 'A' + (rand() % 25);
    newData.postcode[6] = 'Z' - (rand() % 25);
    newData.postcode[7] = '\0';

    for(int j = 0; j < 250; ++j){
        newData.info1[j] = '+';
        newData.info2[j] = '*';
        newData.info3[j] = '-';
    }

    newData.info1[250] = '\0';
    newData.info2[250] = '\0';
    newData.info3[250] = '\0';

    int offset = file->writeRecord(&newData);
    index->setOffset(i, offset);
}