std::istream::read doesn't return the last part of the file

[vestal plaza]

Hello! I am using std::istream::read to read the contents of a file, N bytes at a time. I noticed that the last part of the file is not returned.

    string fname = "output/input";
    ifstream inputfile (fname);
    if (!inputfile.is_open()) {
        fprintf(stderr, "Failed to open input file, reason: %d\n", errno);
        exit(1);
    }

    vector<char> vec(seg_size - sizeof(int));
    while(inputfile.read(vec.data(), vec.size())) {
        vec.resize(inputfile.gcount());
        process_input_part(vec);
        vec.resize(seg_size - sizeof(int));
    }

relevant stackoverflow post: https://stackoverflow.com/questions/50491833/how-do-you-read-n-bytes-from-a-file-and-put-them-into-a-vectoruint8-t-using-it

Can you please tell me what I am doing wrong and how I can make sure that the last part of the file is also returned?

[ripe island]

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[celest forum]

when calling read open the file in binary mode, this is crucial for Windows because in text mode, the \r from each newline gets skipped

you claim you can't read the last part, where is this last part

The code looks ok, but the repetitive resizing is very bad for performance, make your process_input_part take in a vector and a count - gcount()

To view exactly what was read, dump it with cout but in hex mode