DFH：Sizeof(Object) 使用 fin.seekg() 给出奇怪的输出；

Question

函数如下：

void debugged_read()
{
    clrscr();
    stu S1;
    ifstream fin;
    eof=false;

    fin.open("CP2.dat", ios::binary);   //Opens the file again
    while(fin.eof() == false) {
        cout<<"\n\n Initial location: "<<fin.tellg();
        fin.read((char*)& S1, sizeof(S1)); //Reads a Record into fin stream
        S1.show();
        cout<<"\n\n After Read location: "<<fin.tellg();


        fin.read((char*)& S1, sizeof(S1)); //Reads the next record space for eof detection
        cout<<"\n Check position: "<<fin.tellg();
        if(fin.eof() == true) {
            cprintf("\nWARNING: End of file Incoming!");
            break;  //Break on eof encounter
        }
        else {
            fin.seekg(-(sizeof(S1)), ios :: cur);  //File Pointer Correction
            cout<<"\n File Pointer Corrected: "<<fin.tellg();
        }
    }
cout<<"\nRead Successful!";
fin.close();
}

如果我使用 long 变量存储 'stu' class 的对象 S1 的大小，此函数将返回预期输出。

但使用 sizeof();它直接给出了这个奇怪的输出：

Answer 1

sizeof returns size_t 即 unsigned int

istream::read 期望 streamsize 即 signed int

DFH：Sizeof(Object) 使用 fin.seekg() 给出奇怪的输出；

DFH: Sizeof(Object) giving weird output with fin.seekg();

file-handling

turbo-c++