由 fread 读取的许多字符

Question

Im am trying to open a file in binary mode and write the content to a buffer in C++. I am using fread for this. However something goes wrong. My code is:

FILE * in = fopen("in", "rb");
_in = new unsigned char [length_in];
fread(_in, sizeof(char), length_in, in);

When debugging i can see that _in = unsigned char * "Asdfghjkl\\x1f \\x10" .

When rebuilding the program, the part \\x1f \\x10 changes randomly or disappears.

What i am expecting is always _in = unsigned char * "Asdfghjkl" .

When replacing length_in with 9 i still get something like "Asdfghjkl\\x1f \\x10" .

What am I missing. I am using a Mac and Xcode.

Answer 1

Your array is created uninitialized, so those are garbage values from whatever was in memory beforehand. Initialize it to zeros like this:

_in = new unsigned char [length_in]();

Also fread returns the number of bytes read. If you're treating it like a string, make sure the result is null-terminated.