DWORD to LPDWORD conversion errors

Question

I am currently trying to build platform-specific implementations for a generic function, and I get weird compilation errors on the WIN32 version. This function is a simple one: it provides the path of the application's configuration file, and the Windows version should logically get it from a registry key.

The current implementation of that function looks like this:

#include <windows.h>

#include <memory>
#include <exception>
#include "../../common/bserrors.h"
#include "bsplatformsettings.h"
#include "bsplatformimpl.h"

std::string bsConfigFileAccessorImpl::ProvideFile() {
    HKEY    key = 0;
    DWORD   buffersz;
    std::string result;

    // Open registry key
    if (RegOpenKey(BSPS_FA_REGKEYGROUP, TEXT(BSPS_FA_REGKEYPATH), &key) != ERROR_SUCCESS) {
        throw bsError(bsErrcode::BSEC_INVALID_CONFIG_ACCESS, BSPS_FA_REGKEYPATH);
    }

    // Get the configuration file path
    if (RegQueryValueEx(key, TEXT(BSPS_FACONF_REGKEYNAME), NULL, REG_SZ, NULL, &buffersz) != ERROR_SUCCESS) {
        RegCloseKey(key);
        throw bsError(bsErrcode::BSEC_INVALID_CONFIG_ACCESS, BSPS_FACONF_REGKEYNAME);
    } else {
        char * buffer = new char[(size_t) buffersz];
        RegQueryValueEx(key, TEXT(BSPS_FACONF_REGKEYNAME), NULL, REG_SZ, (LPBYTE) buffer, &buffersz);

        result = std::string(buffer);
        delete(buffer);
    }

    RegCloseKey(key);
    return result;
}

However, when I am trying to compile that version, I get puzzling errors:

platform/win32/bsplatformimpl.cpp: In member function 'virtual std::string bs::bsConfigFileAccessorImpl::ProvideFile()':
platform/win32/bsplatformimpl.cpp:228:87: error: invalid conversion from 'int' to 'LPDWORD {aka long unsigned int*}' [-fpermissive]
if (RegQueryValueEx(key, TEXT(BSPS_FACONF_REGKEYNAME), NULL, REG_SZ, NULL, &buffersz) != ERROR_SUCCESS) {
                                                                            ^
platform/win32/bsplatformimpl.cpp:233:95: error: invalid conversion from 'int' to 'LPDWORD {aka long unsigned int*}' [-fpermissive]
RegQueryValueEx(key, TEXT(BSPS_FACONF_REGKEYNAME), NULL, REG_SZ, (LPBYTE) buffer, &buffersz);
                                                                                   ^

Looks like the DWORD definition presented at compilation time is not the one we would expect. However I don't define any custom DWORD definition anywhere and the DWORD definition in windows.h looks fine (aka. unsigned long int).

So where does that plain int come from? I'm very, very puzzled by these errors...

Does anyone get some ideas about what may be causing this and how to solve this?

The problematic port uses the following: Target system: windows XP 32 / Compiler: mingw32-gcc-g++ 4.8.1-4 / Compiler options: -pedantic-errors -Wall -Werror -Wextra -std=c++11

Thank you!!

Answer 1

It's complaining about the fourth argument, REG_SZ.

You're passing a value of the type you expect. But the function requires you to pass a buffer which receives the actual type.

lpType [out, optional]

A pointer to a variable that receives a code indicating the type of data stored in the specified value. For a list of the possible type codes, see Registry Value Types. The lpType parameter can be NULL if the type code is not required.

So you need something like:

DWORD dwActualType;

RegQueryValueEx(key, TEXT(BSPS_FACONF_REGKEYNAME), NULL, &dwActualType, (LPBYTE) buffer, &buffersz);
if (dwActualType == REG_SZ) ...