C ++覆盖特定位置文件中的数据 [英] C++ overwriting data in a file at a particular position

问题描述

我有问题覆盖一些在c + +中的文件中的数据。我使用的代码是

pre $ code int main（）{
fstream fout;
fout.open（hello.txt，fstream :: binary | fstream :: out | fstream :: app）;
pos = fout.tellp（）;
fout.seekp（pos + 5）;
fout.write（####，4）;
fout.close（）;
返回0;

}

使用seekp，数据总是写在最后。我想写在一个特定的位置。
如果我不添加fstream ::应用程序，文件的内容被删除。
Thanks。

解决方案

问题在于 fstream :: app - 它打开要附加的文件，这意味着所有写入文件的末尾。为了避免内容被删除，请尝试打开 fstream :: in ，这意味着打开 fstream :: binary | fstream :: out | fstream :: in 。

i m having problem in overwriting some data in a file in c++. the code i m using is

 int main(){
   fstream fout;
   fout.open("hello.txt",fstream::binary | fstream::out | fstream::app);
   pos=fout.tellp();
   fout.seekp(pos+5);
   fout.write("####",4);
   fout.close();
   return 0;

}

the problem is even after using seekp ,the data is always written at the end.I want to write it at a particular position. And if i dont add fstream::app , the contents of the file are erased. Thanks.

解决方案

The problem is with the fstream::app - it opens the file for appending, meaning all writes go to the end of the file. To avoid having the content erased, try opening with fstream::in as well, meaning open with fstream::binary | fstream::out | fstream::in.

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