Access violation reading location when using ReadFile - c++

Question

I`m struggling for the past many hours with the following problem: I try to read a file using CreateFile and ReadFile methods.
Here is the code:
char* Utils::ReadFromFile(wchar_t* path) {
HANDLE hFile = CreateFile(
path, // long pointer word string file path (16 bit UNICODE char pointer)
GENERIC_READ, // access to file
0, // share mode ( 0 - prevents others from opening/readin/etc)
NULL, // security attributes
OPEN_EXISTING, // action to take on file -- returns ERROR_FILE_NOT_FOUND
FILE_ATTRIBUTE_READONLY, // readonly and offset possibility
NULL // when opening an existing file, this parameter is ignored
);
if (hFile == INVALID_HANDLE_VALUE) {
std::cout << "File opening failed" << endl;
std::cout << "Details: \n" << Utils::GetLastErrorMessage() << endl;
CloseHandle(hFile);
hFile = NULL;
return nullptr;
}
LARGE_INTEGER largeInteger;
GetFileSizeEx(hFile, &largeInteger);
LONGLONG fileSize = largeInteger.QuadPart;
if (fileSize == 0) {
std::cout << "Error when reading file size" << endl;
std::cout << "Details: \n" << Utils::GetLastErrorMessage() << endl;
CloseHandle(hFile);
hFile = NULL;
return nullptr;
}
cout << "File size: " << fileSize << endl;
char* bytesRead;
bytesRead = new char(fileSize);
int currentOffset = 0;
int attempts = 0;
int nBytesToBeRead = BYTES_TO_READ;
//DWORD nBytesRead = 0;
OVERLAPPED overlap{};
errno_t status;
while (currentOffset < fileSize) {
overlap.Offset = currentOffset;
if (fileSize - currentOffset < nBytesToBeRead)
nBytesToBeRead = fileSize - currentOffset;
status = ReadFile(
hFile, // file handler
bytesRead + currentOffset, // byted read from file
nBytesToBeRead, // number of bytes to read
NULL, // number of bytes read
&overlap // overlap parameter
);
if (status == 0) {
std::cout << "Error when reading file at offset: " << currentOffset << endl;
std::cout << "Details: \n" << Utils::GetLastErrorMessage() << endl;
attempts++;
std::cout << "Attempt: " << attempts << endl;
if (attempts == 3) {
cout << "The operation could not be performed. Closing..." << endl;
CloseHandle(hFile);
hFile = NULL;
return nullptr;
}
continue;
}
else {
cout << "Read from offset: " << currentOffset;// << " -- " << overlap.InternalHigh << endl;
currentOffset += nBytesToBeRead;
if (currentOffset == fileSize) {
cout << "File reading completed" << endl;
break;
}
}
}
CloseHandle(hFile);
return bytesRead;
}
When running this method I get some weird results:
One time it worked perfectly
Very often I get Access violation reading location for currentOffset variable and overlap.InternalHigh ( I commented last one), with last method from CallStack being
msvcp140d.dll!std::locale::locale(const std::locale & _Right) Line 326 C++
Sometimes the function runs perfectly, but I get access violation reading location when trying to exit main function with last method from CallStack being
ucrtbased.dll!_CrtIsValidHeapPointer(const void * block) Line 1385 C++
I read the windows documentation thoroughly regarding the methods I use and checked the Internet for any solution I could find, but without any result. I don't understand this behaviour, getting different errors when running cod multiple times, and therefore I can`t get to a solution for this problem.
Note: The reason I am reading the file in repeated calls is not relevant. I tried reading with a single call and the result is the same.
Thank you in advance

Answer 1

You are allocating a single char for bytesRead, not an array of fileSize chars:
char* bytesRead;
bytesRead = new char(fileSize); // allocate a char and initialize it with fileSize value
bytesRead = new char[fileSize]; // allocate an array of fileSize chars