问：关于QT的memmove（）和memcpy（）（c ++）

Question

simple question, I have problem with memmove() and memcpy() when i'm using it. I really don't understand what wrong with my code. by the way i use QT.

HANDLE hFile;
HANDLE hMapFile;
HANDLE hMapView;

hFile = CreateFileW((const wchar_t*) objPath.constData(), GENERIC_READ , 0, NULL, OPEN_EXISTING, 0, NULL);
if (hFile != INVALID_HANDLE_VALUE){

    hMapFile = CreateFileMappingW(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
    if (hMapFile != INVALID_HANDLE_VALUE){

        hMapView = MapViewOfFile(hMapFile, GENERIC_READ, 0, 0,0);
        if (hMapView != INVALID_HANDLE_VALUE){
            uint DefineWord;
            memmove((void *) &DefineWord, hMapView,2); // <- always error right here
            qDebug()<<DefineWord;
        }
    }
}

Answer 1

hMapView is not a pointer. memmove requires two pointers. Fix this by declaring hMapView properly. It should be a LPVOID .

Answer 2

MapViewOfFile returns a pointer, or NULL (0) when there is an error, not INVALID_HANDLE_VALUE (-1).

Edit: There was a lot of other problems with your code:

• QString::constData() returns QChar* , not wchar_t* , you have to use QString::utf16() instead.
• If CreateFileMappingW fails it returns NULL , not INVALID_HANDLE_VALUE .
• MapViewOfFile access parameter is FILE_MAP_READ , not GENERIC_READ .
• uint is often bigger than 2 bytes, so you should initialize the variable to 0 before memmove if you only read 2 bytes.

Here is a minimal code that should work (only tested on wineg++/wine):

#include <windows.h>
#include <QtCore/QString>
#include <QtCore/QDebug>
#include <QtCore/QTextStream>

int main(int argc, char const *argv[])
{
    if (argc < 2) {
        QTextStream(stdout) << "Usage :" << argv[0] << " filename" << endl;
        return 1;
    }

    QString objPath(argv[1]);
    // Qt source uses C-Style cast from utf16() to (wchar_t*),
    // so it should be safe
    HANDLE hFile = CreateFileW((const wchar_t *) objPath.utf16(), GENERIC_READ, 0, NULL, OPEN_EXISTING, 0, NULL);
    if (hFile == INVALID_HANDLE_VALUE) {
        qDebug() << qt_error_string(); 
    } else {
        HANDLE hMapFile = CreateFileMappingW(hFile, NULL, PAGE_READONLY, 0, 0, NULL);
        if (!hMapFile) {
            qDebug() << qt_error_string(); 
        } else {
            void *pMapView = MapViewOfFile(hMapFile, FILE_MAP_READ, 0, 0, 0);
            if (!pMapView) {
                qDebug() << qt_error_string();
            } else {
                uint DefineWord = 0;
                memmove((void *) &DefineWord, pMapView, 2);
                qDebug() << DefineWord;
            }
            CloseHandle(hMapFile);
        }
        CloseHandle(hFile);
    }
    return 0;
}

PS: QString qt_error_string(int errorCode = -1) is an apparently undocumented Qt function that returns the error string of the last error (from the error code returned from GetLastError() or errno ).

If you are using Qt, you can map a file to memory with QFile::map() .
To do what your initial code was supposed to do, you only had to add 2 lines to the code sample you found (plus the error checking):

QFile file("foo"); 
if(!file.open(QFile::ReadOnly)) {
   qDebug() << file.errorString();
} else {
    uchar *memory = file.map(0, file.size()); 
    if (!memory) {
        qDebug() << file.errorString();
    } else {            
        uint DefineWord = 0;
        memmove(&DefineWord, memory, 2);

        file.unmap(); 
    }
} 

Answer 3

by the way i use QT.

You aren't really using it in your example. Qt has QFile::map method which can (and in my opinion should) be used instead of platform-specific MapViewOfFile.