malloc pointer function passing fread

Question

Can't figure out what's wrong, I don't seem to be getting anything from fread.

port.h

#pragma once
#ifndef _PORT_
    #define _PORT_
    #include <string>
    #ifndef UNICODE
        typedef char chr;
        typedef string str;
    #else
        typedef wchar_t chr;
        typedef std::wstring str;
        inline void fopen(FILE ** ptrFile, const wchar_t * _Filename,const wchar_t * _Mode)
        {
            _wfopen_s(ptrFile,_Filename,_Mode);
        }
    #endif
#endif

inside main()

    File * f = new File(fname,FileOpenMode::Read);
    chr *buffer;
    buffer = (wchar_t*)malloc(f->_length*2);
    for(int i=0;i<f->_length;i++)
    {
      buffer[i] = 0;
    }
    f->Read_Whole_File(buffer);
    f->Close();
    for(int i=0;i<f->_length;i++)
    {
      printf("%S",buffer[i]);
    }
    free(buffer);

inside file class

    void Read_Whole_File(chr *&buffer)
    {
        //buffer = (char*)malloc(_length);
        if(buffer == NULL)
        {
            _IsError = true;
            return;
        }
        fseek(_file_pointer, 0, SEEK_SET);
        int a = sizeof(chr);
        fread(&buffer,_length ,sizeof(chr) , _file_pointer);            
    }

Answer 1

You're mixing pointers and references all over the place.

Your function only needs to take a pointer to the buffer:

void Read_Whole_File(char *buffer) { ... }

And you should pass that pointer as-is to fread() , don't take the address of the pointer:

size_t amount_read = fread(buffer, _length, sizeof *buffer, _file_pointer);

Also remember:

• If you have a pointer ptr to some type, you can use sizeof *ptr and remove the need to repeat the type name.
• If you know the length of the file already, pass it to the function so you don't need to figure it out twice.
• In C, don't cast the return value of malloc() .
• Check for errors when doing memory allocation and I/O, things can fail.

Answer 2

buffer is a reference to a chr * . Yet you're reading into &buffer which is a chr ** (whatever that is). Wrong.

You don't even need to pass a reference to buffer in Read_Whole_File , just use a regular pointer.

Answer 3

aside from your original problem...

from your code:

typedef char chr;

chr *buffer;
buffer = (wchar_t*)malloc(f->_length*2);
for(int i=0;i<f->_length;i++)
{
  buffer[i] = 0;
}

don't you think there is something wrong here ? in case you cannot spot the errors, here is the list:

• chr is a char , so buffer is a char *
• you are using malloc . are you coding in C or in C++ ? if it is C++, consider using new
• the buffer you allocate is explicitly casted to a wchar_t * but buffer is a char *
• in the malloc you are allocating a block of size length*2 when you should be using length * sizeof(w_char_t) . don't make any assumption on the size of a type (and even writing sizeof(char) is no problem, it renders the intentions explicit)
• the for loop goes from 0 to length , but since buffer is defined as a buffer of char , only length bytes are initialized, whereas you alocated length*2 bytes, so half your buffer is still uninitialized.
• memset() has been defined to avoid this kind of for loop...

please be a little bit careful when coding !

Answer 4

First a couple of nits:

• What's with the malloc and free? What's wrong with new and delete? You are obviously writing C++ here, so write C++ .
• Overloading fopen, fseek, fread in the case of wchar_t bothers me, immensely. Much better: Use templates, or define your own functions. Don't overload those names that belong to C.

This is not not a nit. The following is almost certainly not doing what you want:

fread(&buffer,_length ,sizeof(chr) , _file_pointer);

chr here is a pointer to a reference, so sizeof is almost certainly going to be either 32 or 64.