Inserting text into file at specific offset using Win32 API

I am looking for a way to make speedy modifications to large multi-gigabyte files. Do the Win32 API support the ability to insert text into a file at a specific offset without having to rewrite the entire file back to disk from the very beginning or from the offset of the change?

Consider an example. Let's say we have the text "test" repeated over and over in a file开发者_如何学Python that is 1 GB in size. If I want to go to the 500 MB offset and insert the text "new", is there a way to insert it without having to rewrite the entire file from the beginning, and/or without having to rewrite the last 500 MBs of it?

Can it be done using Win32 API? If not, are there any strategies to optimize a text insertion operation like this to maximize speed?

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There are methods to rewrite only the portion after the insertion point, but generally, no - to insert something at a particular point in a file, you must re-write everything after that point.

This boils down to the way files are stored on disk - typically in chunks, such that this operation is either not possible or not easy. For 99% of the cases, this doesn't matter, so the API doesn't expose a way of doing this.

If you have control over the file format, you can engineer ways such that you can write data to the end of the file, but have some tracking data to say "this stuff really belongs here".

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When you open the file in read-write mode, you can write data in the middle of the file, yet this will override existing data. There's no easy way to insert the data to the file.

However to make your life easier when you have a 64-bit system (on 32-bit system this won't work in your particular scenario) it makes sense to employ memory-mapped file. With file API you need to copy the tail in a tricky way. With MMF you do the following: 1. Create a file mapping and map the file to memory 2. Move the tail further by moving the memory block using memmove or similar function which cares for overlapping blocks. 3. put your bytes in the middle.

With this approach memory manager will do most work for you.

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You can't do this. What you can do efficiently is append to a file. You'd need to build some structure into your file format if you wanted to take advantage of this, as Thanatos has described.

As usual, Raymond Chen has something to say on the matter. He's talking about deleting from the beginning of the file but the issues are essentially the same as for this question.