Understanding the design of std :: istream :: read

Question

std::istreamhas a prototype istream& read (char* s, streamsize n), the actual number of bytes read must be obtained by calling istream::gcount(), also the reliability istreamcan be known from ios::good.

I discussed the implementation of another thread class that I was trying to write with my colleague, where I said that I could follow this design; but he said instead of invoking the gcount user each time, one could read a prototype like this istream& read (char* s, streamsize n, size_t &bytes_read)so that it would go into one call, and the first would be awkward. I could not protect the design choice std. What is the true rationale istream::read?

Answer 1

I suppose, because C ++ usually does not force an interface that everyone might not need. If you need readto accept a parameter that some people do not care about, then it causes additional coding work (declaring an additional int to pass as a parameter). It also always saves read bytes regardless of whether the client cares or not (some clients may just take care that the read fails as indicated by the eof / fail bits).

Using a separate method, you remove the interface for various pieces of information that may or may not be needed.

Answer 2

Try the readsome command instead,

streamsize readsome ( char* buf, streamsize num );

buf - , num - , , , .

- .

, :

char buf[BUF_SIZE]
streamsize bytesRead;
do
{
   bytesRead = instr.readsome( buf, BUF_SIZE );
   // do stuff with the bytes you read, if any
} while ( bytesRead == BUF_SIZE );

Answer 3

std::istream istream& read (char* s, streamsize n) istream::gcount(), istream ios::good.

istream::read(char* s, streamsize n) ( NULL ) n s. s char, istream::read . , istream, ( , ):

unsigned int count;
input.read(reinterpret_cast<char*>(&count), sizeof(count));
double* data = new double[count];

for (unsigned int i = 0; i < count; ++i)
    input.read(reinterpret_cast<char*>(data[i]), sizeof(double));

istream::gcount() , istream::read. , count, , a double, istream::gcount() data.

Answer 4

, , C , . , , , , , , , . , , -.

Cash Cow , . IO , while , . , , , -, IO.

, , while, EOF. , - , , , .

, readsome - .

: readsome ( V++). .