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

问题描述

我试图打开一个只写一个二进制文件，但不删除的内容。但我不希望写入EOF。我想要写在文件中的特定位置。

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.

下面是豆蔻例如：

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();

如果使用的应用程序，寻求不起作用。如果不使用的应用程序打开文件擦除数据。是否有人知道答案？

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，它允许您提供一个偏移量和的方向的，这可能会在你的情况下开始时的文件（即的ios_bas​​e ::求）。当然，这可以让你知道你在做什么，你想要做的是覆盖现有的字符数。

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.

编辑：这是完全的例子：

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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