写函数不使用seekp值 [英] Write function not using the seekp value

问题描述

我正在尝试使用C ++在文件中的特定位置写入条目

I'm trying to use C++ to write an entry in a specific place in a file

基本上我有

ofstream ofs("file.dat", ios::binary | ios::app);
ofs.seekp(220, ios::beg);
ofs.write((char *)&i, sizeof(i));

但是无论我做什么，它总是写在文件末尾.

But no matter what I do it always write at the end of the file.

我认为这与iso::app有关，因为根据文档

I suppose this is related to iso::app because according to the documentation

app (append) Set the stream's position indicator to the end of the stream before each output operation

但是，如果我使用 ate 或不执行任何操作，它将始终删除文件的内容.

But if I use ate or nothing it always erases the content of the file.

任何帮助都会很棒:)

推荐答案

是的，正是ios::app导致了这种行为.将其替换为ios::in | ios::out.

Yes, it's the ios::app that's causing this behaviour. Replace it with ios::in | ios::out.

编辑:您的问题尚不清楚，但是您的注释表明您正在尝试插入数据到文件中间，而不是覆盖文件的一部分.如果确实如此，您几乎必须为此使用第二个文件.

edit: It wasn't clear from your question, but your comments suggest that you're trying to insert data in the middle of the file, rather than overwrite a portion of the file. If that is indeed the case, you pretty much have to use a second file for that.

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