wrong output by vs2017 but mingw works - c++

Question

I wrote a simple function to load a char * buffer from a file but when compiled through vs2017 it add rubbish at the end of the buffer but mingw compiled exe gives correct output
the function looks like something
#include <stdio.h>
#include <stdlib.h>
using namespace std;
char * loadfromfile(const char * _Filename)
{
char * buffer;
FILE * file = fopen(_Filename, "r");
if (!file)
return nullptr;
fseek(file, 0, SEEK_END);
auto _length = ftell(file);
buffer = new char[_length + 1];
rewind(file);
printf("characters read(loadformfile()) :%i\n",fread(buffer, sizeof(char), _length, file));
buffer[_length] = '\0';
fclose(file);
return buffer;
}
int main() {
char * str = loadfromfile("D:\\shutdown.bat");
printf("%s\n", (str) ? str : "failed to load");
delete[] str;
return 0;
}
VS2017 output:
characters read(loadformfile()) :86
#echo off
Set minutes=30
set /a seconds=%minutes%*60
TIMEOUT /T %seconds%
shutdown /s
\inst
g++ (x86_64-posix-seh-rev0, Built by MinGW-W64 project) 7.1.0 output:
characters read(loadformfile()) :zu
#echo off
Set minutes=30
set /a seconds=%minutes%*60
TIMEOUT /T %seconds%
shutdown /s
file is:
#echo off
Set minutes=30
set /a seconds=%minutes%*60
TIMEOUT /T %seconds%
shutdown /s
EDIT:
A working solution
char * loadfromfile(const char * _Filename)
{
char * buffer;
FILE * file = fopen(_Filename, "r");
if (!file)
return nullptr;
fseek(file, 0, SEEK_END);
auto _length = ftell(file);
buffer = new char[_length + 1];
rewind(file);
buffer[fread(buffer, sizeof(char), _length, file)] = '\0';
fclose(file);
return buffer;
}

Answer 1

You can't portably use fseek()/ftell() to get the size of a file.
Per the C Standard, footnote 268, p 301:
Setting the file position indicator to end-of-file, as with
fseek(file, 0, SEEK_END), has undefined behavior for a binary
stream ...
and
7.21.9.2 The fseek function
... A binary stream need not meaningfully support fseek calls with a
whence value of SEEK_END.
So you can't reliably use fseek() to get to the end of a binary file. In fact, doing so is specifically stated by the C Standard to be undefined behavior.
OK, so you can use fseek() to get to the end of a file opened in text mode, but
7.21.9.4 The ftell function
...
For a text stream, its file position indicator contains unspecified
information, usable by the fseek function for returning the file
position indicator for the stream to its position at the time
of the ftell call; the difference between two such return
values is not necessarily a meaningful measure of the number of
characters written or read.
On a text file, ftell() doesn't return a value useful in getting the file size.
In short, using fseek()/ftell() to get the size of a file is fundamentally broken. The fact that it works sometimes is just an implementation detail.