为什么tellp（）给出-1？

Question

我正在尝试学习fstream，这是我在VS2019上运行的代码：

#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;

int main() {
    //cout << "lOOKING IN FILE";
    string s;
    fstream dictionary("C:/Users/source/repos/Test2/Test2/Text.txt");
    if (!dictionary) // were there any errors on opening? 
        exit(-1);
    while (dictionary >> s) cout << s << '\n'; // Print all names in file
    dictionary.seekp(0, ios::beg); // Go back to beginning of file
    cout << dictionary.tellp() << endl; 
    dictionary >> s;
    cout << s; // Print the first name
    return 0;
}

输出为：

abc
acb
cab
-1
cab

为什么tellp给出-1而不转到文件的开头？

Answer 1

您需要clear流的状态。