How to fix CopyFile() error 5 - access denied error - c++

Question

I am trying to write a copy file function that can be used on both Linux and Windows. It works on Linux, but on Windows, I get error code 5 when trying to use the WinApi function CopyFile().
In header File.h
This is the custom defined function in the File namespace that I should be able to use on both Linux and windows.
class File
{
public:
static bool copyFile(std::string source, std::string destination);
private:
}
In File.cpp
For Linux it is simple:
#ifdef __unix__
#include "File.h"
bool File::copyFile(std::string source, std::string destination)
{
std::string arg = source + " " + destination;
return launchProcess("cp", arg);
}
#endif
In the Windows specific block of code, I use the WinAPI (#include < windows.h >) function CopyFile(). This accepts LPCWSTR data types instead of strings. To overcome this I have created a function that converts strings to LPCWSTR types.
#ifdef _WIN32
#include "File.h"
#include <Windows.h>
std::wstring strtowstr(const std::string &str)
{
// Convert an ASCII string to a Unicode String
std::wstring wstrTo;
wchar_t *wszTo = new wchar_t[str.length() + 1];
wszTo[str.size()] = L'\0';
MultiByteToWideChar(CP_ACP, 0, str.c_str(), -1, wszTo,(int)str.length());
wstrTo = wszTo;
delete[] wszTo;
return wstrTo;
}
bool File::copyFile(std::string source, std::string destination)
{
std::wstring wsource = strtowstr(source);
std::wstring wdestination = strtowstr(destination);
int result = CopyFileW(wsource.c_str(), wdestination.c_str(), TRUE);
//for debugging...
std::wcout << "The error is " << GetLastError() <<std::endl;
std::wcout << wsource.c_str() << std::endl;
std::wcout << wdestination.c_str() << std::endl;
if (result == 0)
{
return false;
}
return true;
}
#endif
In my Test Programme
TEST(all,main_copy_file)
{
std::cout << "Testing copyFile() function..." << std::endl;
std::string srcDir = File::currentWorkingDirectory() + "srcDir";
File::makeDirectory(srcDir);
std::string destDir = File::currentWorkingDirectory() + "destDir/";
File::makeDirectory(destDir);
File::makeFile(srcDir, "testFile", ".txt");
ASSERT_TRUE(File::fileExists(srcDir + "/testFile.txt")) << "Error: Test file has not been generated" << std::endl;
ASSERT_TRUE(File::directoryExists(destDir)) << "Error: Destination directory does not exist" <<std::endl;
ASSERT_TRUE(File::copyFile(srcDir + "/testFile.txt", destDir)) << "Error: Coppy unsucsessfull" << std::endl;
ASSERT_TRUE(File::fileExists(destDir + "/testFile.txt")) << "Error: CoppyFile() flagged as sucsessfull but file does not exist" << std::endl;
}
In the application Output (on Windows)
/*
Testing copyFile() function...
The error is 5
C:\GIT\CorteX\Externals\OSAL\build\Debug/srcDir/testFile.txt
C:\GIT\CorteX\Externals\OSAL\build\Debug/destDir/
error: Value of: File::copyFile(srcDir + "/testFile.txt", destDir)
Actual: false
Expected: true
Error: Coppy unsucsessfull
*/
Error code 5 is an access denied error. I think it gives this error when either the directory does not exist, the directory is open somewhere else, or I do not have permissions.
Since I have tested that the directory does exist, I think it must be one of the latter two. I might only have restricted Admin rights (I don't know), but I can paste into the "destDir" without admin permission. So maybe it thinks the directory is open? Is there a command that exists to make sure the directory is closed?
The test is successful when running on Linux.

Answer 1

The CopyFile API expects file names for both source and destination files. Your code passes a directory name for the destination. This causes the API to fail. You need to append the file name for the destination as well.
Besides that, there are several other issues with your code:
The path separator on Windows is a backslash (\). Your are mixing forward slashes (/) and backslashes. Depending on the arguments passed, the system won't translate forward slashes to backslashes, before passing them on to lower-level file I/O API's.
You are calling GetLastError too late. You need to call it immediately, whenever it is documented to return a meaningful value. Do not intersperse it with any other code, however trivial it may appear to you. That code can modify and invalidate the calling thread's last error code.
Your code assumes ASCII-encoded strings. This will stop working, when dealing with files containing non-ASCII characters. This is quite common.
new wchar_t[...] buys you nothing over std::vector<wchar_t>, except the possibility to introduce bugs.
Your MultiByteToWideChar-based string conversion implementation makes (undue) assumptions about the code unit requirements of different character encodings. Those assumptions may not be true. Have the API calculate and tell you the destination buffer size, by passing 0 for cchWideChar.
Your string conversion routine ignores all return values, making bugs ever so likely, and unnecessarily hard to diagnose.

Answer 2

I know this is an old post, but for anyone who stumbles here needing more help:
CopyFile has the following constraints which if not met can give access denied error:
Insufficient permissions for the current user
File is in use
Filepath is a directory and not a file
File is read-only
In my case all the above were met, still I kept getting the same error. What helped me was a simple
SetFileAttributes(filePath,FILE_ATTRIBUTE_NORMAL)
Retrieving and Changing File Attributes
SetFileAttributes