A simple but detailed explanation of the Windows file map reading data file example

#include <windows.h>
#include <string.h>
#include <string>
#include <iostream>
using namespace Std;

int main (int argc, char *argv[])
{
Step 1 Open the file File_flag_write_through
HANDLE hfile = CreateFile (
"Demo.txt",
Generic_write | generic_read,//if you want to map a file: This must be set to read-only (Generic_read) or read-write
0,//This is set to open file any attempt will fail
Null
Open_existing,
File_attribute_normal,//| File_flag_write_through, "solution 1"
NULL);
if (hfile! = INVALID_HANDLE_VALUE)//File Open failed return handle IS-1
This step must be tested, see step 2 in detail
{
cout<< "file opened successfully ~!\n";
}
Else
{
cout<< "File open failed! \ n ";
DWORD d = GetLastError ();
cout<<d<<endl;
return-1;
}

Step 2 Create a memory-mapped file
DWORD dwfilesize = GetFileSize (hfile, NULL);
printf ("File Size:%d\n", dwfilesize);
HANDLE Hfilemap = createfilemapping (
hfile,//If this value is Invalid_handle_value, it is legal, you must test it on the step.
NULL,//default security
Page_readwrite,//readable/writable
0,//2 x 32 digits for a 64-digit number, maximum file bytes,
High byte, when the file size is less than 4G, the high byte is always 0
0,//dwfilesize,//This is a low byte, which is the main parameter, if 0, take the file true size
NULL);
if (hfilemap! = NULL)
{
cout<< "Memory mapped file creation succeeded ~!\n";
}
Else
{
cout<< "Memory-mapped file creation failed!" "<<endl;
}

Step 3: Map the file data to the address space of the process
PVOID pvfile = MapViewOfFile (//pvfile is the obtained pointer, use it to manipulate the file directly
Hfilemap,
File_map_write,//writable
0,//file pointer header position high byte
0,//file pointer header position low byte must be the integer of the allocation granularity, and the granularity of Windows is 64K
0); The end of the file to be mapped, if 0, from the needle to the end of the real file
if (pvfile! = NULL)
{
cout<< "File data mapped to the address of the process successfully ~!\n";
}
Else
{
cout<< "File data mapped to the address of the process successfully ~!\n";
}

Step 4: Manipulate the file as you would any memory, and demonstrate the ability to reverse the entire file
Char *p = (char*) pvfile;
printf ("%s\n", p);
for (unsigned int i = 0; I <= dwfilesize/2; i++)
{
int ntmp = P[i];
P[i] = p[dwfilesize-1-i];
P[dwfilesize-1-I] = ntmp;
}
printf ("%s\n", p);

cout<< "Swap complete, click Enter to exit" <<endl;

Step 5: Related release work
UnmapViewOfFile (Pvfile); Release the head pointer of the memory-mapped file
CloseHandle (HFILEMAP); Memory-mapped file handle
CloseHandle (hfile); Close File
GetChar ();
return 0;
}

A simple but detailed explanation of the Windows file map reading data file example