使用C 中的Fstream读取和附加文件

reading and appending a file using fstream in C++

本文关键字：文件 读取 中的 Fstream 使用      更新时间：2023-10-16

我正在尝试使用fstream读取文件。然后，当我到达结尾时，我附加文件并写一些员工文件

abc

我写了示例代码

#include<iostream>
#include<fstream>
#include<queue>
using namespace std;
int main(int argc, char **argv){
    fstream *binf;
    binf=new fstream("t.txt", ios::out|ios::in|ios::app);
    cout<<"EOF"<<EOF<<endl;
    while(true){
        cout<<"before peek"<<endl;
        cout<<"binf->tellg:"<<binf->tellg()<<endl;
        cout<<"binf->tellp:"<<binf->tellp()<<endl;
        cout<<"binf->peek()::int=("<<(int)binf->peek()<<")::char=("<<(char)binf->peek()<<")"<<endl;
        cout<<"after peek"<<endl;
        cout<<"binf->tellg:"<<binf->tellg()<<endl;
        cout<<"binf->tellp:"<<binf->tellp()<<endl;
        char c;
        if(binf->peek()==EOF){
            cout<<"file is not good"<<endl;
            break;
        }
        binf->get(c);
    }
    cout<<"binf->tellg:"<<binf->tellg()<<endl;
    cout<<"binf->tellp:"<<binf->tellp()<<endl;
    binf->seekg(3);
    binf->seekp(3);
    cout<<"binf->tellg:"<<binf->tellg()<<endl;
    cout<<"binf->tellp:"<<binf->tellp()<<endl;
    binf->put('H');
    cout<<"binf->tellg:"<<binf->tellg()<<endl;
    cout<<"binf->tellp:"<<binf->tellp()<<endl;
    binf->seekg(4);
    char c;
    binf->get(c);
    cout<<"c:"<<c<<endl;
    binf->clear();
    binf->close();
    delete binf;
    return 0;
}

这是我从运行此代码中获得的输出

EOF-1
before peek
binf->tellg:0
binf->tellp:0
binf->peek()::int=(97)::char=(a)
after peek
binf->tellg:0
binf->tellp:0
before peek
binf->tellg:1
binf->tellp:1
binf->peek()::int=(98)::char=(b)
after peek
binf->tellg:1
binf->tellp:1
before peek
binf->tellg:2
binf->tellp:2
binf->peek()::int=(99)::char=(c)
after peek
binf->tellg:2
binf->tellp:2
before peek
binf->tellg:3
binf->tellp:3
binf->peek()::int=(10)::char=(
)
after peek
binf->tellg:3
binf->tellp:3
before peek
binf->tellg:4
binf->tellp:4
binf->peek()::int=(-1)::char=(ÿ)
after peek
binf->tellg:-1
binf->tellp:-1
file is not good
binf->tellg:-1
binf->tellp:-1
binf->tellg:-1
binf->tellp:-1
binf->tellg:-1
binf->tellp:-1
c:

我要做的就是修复文件并在最后写但是，每当我在文件末尾看到eof时，文件不再使用即使使用peek（）

击中文件末尾时，将 fstream放入错误状态中。当它处于错误状态时，除非您清除错误状态，否则什么都不会工作。所以你需要这个

   if(binf->peek()==EOF){
        cout<<"file is not good"<<endl;
        binf->clear(); // clear the error state
        break;
   }

您不需要在关闭它之前清除fstream。

btw好的调试技术，但是如果您学会使用适当的调试器，您会发现这更容易。

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