Thread: std::ofstream strange behavior when writing binary

Hi,
I have a code that outputs the content of an array of std::maps in binary format.

Code:

auto outfile = std::fstream(output, std::ios::out | std::ios::binary);
MatchedPair tmp;
for (int i = 0; i < sizeArray; ++i)
{ 
    for (auto itr = arr[i].cbegin(); itr != arr[i].cend(); ++itr)
    {   
        tmp.ID2 = itr_in->first;
        tmp.distance = itr_in->second;
        outfile.write((char*)&tmp, sizeof(MatchedPair));
    }   
} 
outfile.close();

The amount of maps depends on an external parameter, but it should always output the same binary file (the total amount of data is always the same).

The problem I am having is that the outputs in binary do not much, but when I translate them into txt they are actually the same!!! I am using bash cmp utility to do the check.

When comparing the binary, the difference cmp it finds is the following:

Code:

 output_1.bin output_2.bin differ: byte 3473657, line 8763 is  15 ^M  16 ^N

I honestly don't know the source of the difference and why when converting them back to txt they are actually the same .

In any case, thanks for any help you can give me!

The MatchedPair is a struct:

Code:

struct MatchedPair
{
    uint32_t ID2;
    double distance;
    MatchedPair(): ID2(0), distance(0) {}
    MatchedPair(uint32_t id2, double d):  ID2(id2), distance(d) {}
};

I found out what the error was. It was actually a rounding error that the .txt file didn't show because it was truncating the results.
So, as usual, it was 100% my mistake .
In any case thanks!