CODEWITHSUNDEEP
c++file-io
Ali Somay
Ali Somay

Reputation: 625

Overwriting bytes of a binary file from an offset in C++

In this operation I copy my source binary file first.

Then I wish to start overwriting bytes in the copied file starting from a specific offset.

I move with seekp(offset,std::ios::beg) to the desired position and I start the overwriting process with

file.write(reinterpret_cast<const char*>(&my_vector[0]), my_vector.size()*sizeof(unsigned char));

Then close the file.

When I open processed file in hex editor all the bytes I see before the offset I have started writing are zeros and the bytes I have written with this operation are sucesfully written.

The mode of the stream is std::fstream(path, std::ios::out | std::ios::binary);

Is there something I am missing in this operation?

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Upvotes: 1

Views: 1164

Answers (1)

Cruz Jean
Cruz Jean

Reputation: 2819

If you want to preserve the old contents, open it in in/out mode. i.e. ios::in | ios::out.

Additionally, if you're using std::fstream this is the default behavior, so you could have just used: std::fstream(path, std::ios::binary).

Upvotes: 4

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