C ++从文件读取/写入N个精确字节（甚至是'00'字节）

Question

My task is read file contents and place them into vector array of std::strings, then output from vector to another file.

I managed to solve it for file containing only normal text, but failed with, lets say .bmp Here is .bmp file header:

BM)(     6   (   —  к        Р((

hex shows these are NULL bytes, not whitespaces

42 3d 06 29 28 00 00 00 00 00 36 00 00 00 ...

As a result , executing the following code

char *buffer = new char [50];

ifstream ifs( "file.bmp" , std::ifstream::binary );
ifs >> std::noskipws;

ifs.read( buffer, 50 );

std::string abc(buffer); //output it to other file next

i end up with buffer and abc strings equal to "BM)(6(—кР(( ..." with all nullbytes skipped. ifs.read() was great until now. So whats the most comfortable way to read/write N exact bytes from a file ?

(I did a search but had difficulties with results)

Answer 1

That was lame, but somebody might google this someday so i ll write an answer.

If while debugging you would hover mouse over buffer after calling ifs.read() you would see "BM)(6(—кР(( ..." , but the null bytes are actually there. But (in MSVS) you couldnt see actual bytes buffer has unless you redefine buffer as

char buffer[50];

Next, when making std::string out of buffer, doing

string abc(buffer); // would not copy null bytes to std string,

So do this instead:

string abc(buffer, 50); //copies all bytes.

Now i have the real file contents in the string and if i output abc to other file i will have same data.

PS when checking results use hex editor to see real bytes, dont trust Notepad.