写入现有二进制文件的中间 c++ [英] Write to the middle of an existing binary file c++

问题描述

我正在尝试打开一个二进制文件进行写入而不删除内容.但我不想写eof.我想写入文件中的特定位置.

I'm trying to open a binary file for writing without erasing the content. But I do not want to write to eof. I want to write to a specific position in file.

这是一个小例子:

ofstream out("test.txt", ios::binary | ios::app);
for(int i = 0; i < 100; i++)
    out.put('_');
out.write("Hallo", 5);
out.close();

ofstream out2("test.txt", ios::binary | ios::app);
out2.seekp(10);
out2.write("Welt", 4);
out2.close();

如果使用应用程序，则搜索不起作用.如果不使用应用程序打开文件会删除数据.有人知道答案吗?

If using app, seek doesn't work. If not using app opening file erases data. Does anybody know an answer?

推荐答案

尝试seekp的第二个重载，它允许你提供一个偏移量和一个方向，这个在您的情况下可能是文件的开头(即 ios_base::beg).这当然假设您知道自己在做什么，并且您想做的只是覆盖现有数量的字符.

try the second overload of seekp, which allows you to provide an offset and a direction, this could be begining of file in your case (i.e. ios_base::beg). This of course assumes you know what you are doing and all you want to do is overwrite an existing number of characters.

这里是完整的工作示例:

here is fully working example:

#include <iostream>
#include <fstream>

using namespace std;
int main()
{
  {
    ofstream out("test.txt", ios::binary);
    for(int i = 0; i < 100; i++)
      out.put('_');
    out.write("Hallo", 5);
  }

  {   
    fstream out2("test.txt", ios::binary | ios::out | ios::in);
    out2.seekp(10, ios::beg);
    out2.write("Welt", 4);
  }
}

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