Why does ofstream insert a 0x0D byte before 0x0A?

问题:

I'm outputing an array of unsigned characters in C++ using ofstream fout("filename"); but it produces a spurious character in between. This is the part of the code that makes the problem:

for(int i = 0; i < 12; i++)
fout << DChuffTable[i];

and this is the definition of the array:

unsigned char DChuffTable[12] = {0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B};

In the output file I get a spurious 0x0D between 0x09 and 0x0A. I checked the array in debugging mode right before it's going to get printed and it's not changed. Please tell me what you think of this problem.

回答1:

Your stream is opening in text mode, and since 0x0A is the line feed (LF) character, that's being converted by your stream to 0x0D 0x0A, i.e. CR/LF.

Open your stream in binary mode:

std::ofstream fout("filename", std::ios_base::out | std::ios_base::binary);

Then line ending conversions should not be performed.

This is usually considered a good idea anyway, as streams can go bizarre w.r.t. flushing when in text mode.