How to read a file with CreateFile in C++?

Question

I can read a file with Unicode path like this:

#include "iostream"
#include "windows.h"
using namespace std;

///--- variables ---///
//-- DWORD --//
DWORD dwBytesToRead = 0;

//-- HANDLE --//
HANDLE hFileHandle;

//-- wchar_t array --//
wchar_t a_wcContentsOfFile[999999] = {0};

//-- WINBOOL --//
WINBOOL wbResult;

int main()
{
    hFileHandle = CreateFileW(L"D:\\Çağatay.txt", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if(hFileHandle != NULL)
    {
        wbResult = ReadFile(hFileHandle, a_wcContentsOfFile, 999999 - 1, &dwBytesToRead, NULL);
        if(wbResult != 0)
        {
            if(dwBytesToRead > 0)
            {
                a_wcContentsOfFile[dwBytesToRead + 1] = '\0';
                wprintf(L"%s\n", a_wcContentsOfFile + 1);
            }
        }
        CloseHandle(hFileHandle);
    }

    getchar();
    return 0;
}

I have used this website as guideline:

https://www.installsetupconfig.com/win32programming/windowsfileapis4_22.html

But I want to write contents of the file to wstring, not stdout.

How can I do this?

If you don't need something special from the WinAPI, why not use std::wifstream? Re: " I want to write contents of the file to wstring" - That's a one-liner using std::wifstream . — Ted Lyngmo
– Ted Lyngmo, Commented Sep 2, 2024 at 20:36
@TedLyngmo ifstream does not support non-ASCII paths. For example Ç and ğ are not ASCII. — Çağatay KAYA
– Çağatay KAYA, Commented Sep 2, 2024 at 20:38
Style note: comments that simply repeat the code aren't helpful. //-- HANDLE --// followed by HANDLE hHandle; is just distracting. Not to mention the name hHandle, which says nothing. Windows programs tend to use prefixes like h to describe the type of the variable (h stands for HANDLE), but many folks these days things that's just noise. With or without that prefix, though, give the variable a name that says what it does. hHandle should be something like fileHandle. — Pete Becker
– Pete Becker, Commented Sep 2, 2024 at 20:41
@ÇağatayKAYA What makes you think it doesn't support non-ASCII paths? std::wifstream is(std::filesystem::path(L"D:/Çağatay.txt")); and then std::wstring content(std::istreambuf_iterator<wchar_t>(is), std::istreambuf_iterator<wchar_t>{}); - Done — Ted Lyngmo
– Ted Lyngmo, Commented Sep 2, 2024 at 20:46

Remy Lebeau · Accepted Answer · 2024-09-03 01:47:00Z

ReadFile() has no concept of strings or Unicode, it only knows about raw bytes.

You already know how to read the raw bytes into a wchar_t[] array (assuming the file content is encoded in UCS-2 or UTF-16, that is). Simply assign that array to a std::wstring object afterwards, eg:

std::wstring wContent;

wbResult = ReadFile(hFileHandle, a_wcContentsOfFile, sizeof(a_wcContentsOfFile), &dwBytesRead, NULL);

if(wbResult != 0)
{
    wContent.assign(a_wcContentsOfFile, dwBytesRead / sizeof(wchar_t));
}

If you know the file size ahead of time (ie, from GetFileSize() or equivalent) then you don't even need the wchar_t[] array at all, you can presize the wstring and read directly into its data buffer, eg:

DWORD dwFileSize = GetFileSize(ReadFile(hFileHandle, NULL); 

std::wstring wContent;
wContent.resize(dwFileSize / sizeof(wchar_t));

wbResult = ReadFile(hFileHandle, wContent.data(), wContent.size() * sizeof(wchar_t), &dwBytesRead, NULL);

if(wbResult == 0)
    dwBytesRead = 0;

wContent.resize(dwBytesRead / sizeof(wchar_t));

Also see: How do I read an entire file into a std::string in C++?, the solutions can be adapted for std::wstring.

Collectives™ on Stack Overflow

How to read a file with CreateFile in C++?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related