Reading text from file to unsigned char array, errors while trying to use example [closed]

问题

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Closed 6 years ago.

I'm trying to use example from:

https://stackoverflow.com/a/6832677/1816083 but i have:

invalid conversion from `unsigned char*' to `char*'
initializing argument 1 of `std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::read(_CharT*, std::streamsize) [with _CharT = char, _Traits = std::char_traits<char>]' 
invalid conversion from `void*' to `size_t'

in line:

size_t bytes_read = myfile.read((unsigned char *) buffer, BUFFER_SIZE);

回答1:

Firstly, read() takes a char* rather than unsigned char*. Secondly, it does not return the number of characters read.

Instead, try:

myfile.read((char*)buffer, BUFFER_SIZE);
std::streamsize bytes_read = myfile.gcount();

回答2:

IMHO the compiler's output is quite enought. It tells you, that you're trying to give unsigned char* to function, that waits char*. BTW, there is even a function name

std::basic_istream<_CharT, _Traits>::read(_CharT*, std::streamsize)
[with _CharT = char ...

If you need unsigned chars buffer[ ... ] then cast it to char*

unsigned char buffer[ BUFFER_SIZE ];
ifstream myfile("myfile.bin", ios::binary);
if (myfile)
{
    myfile.read((char*) buffer, BUFFER_SIZE);
    //          ^^^^^^^
    size_t bytes_read = myfile.gcount();
}

来源：https://stackoverflow.com/questions/15266448/reading-text-from-file-to-unsigned-char-array-errors-while-trying-to-use-exampl