How to use NvAPI_DISP_GetDisplayConfig?

Question

When using the NVAPI I'm having problems with NvAPI_DISP_GetDisplayConfig. I get an AppCrash on the second call to NvAPI_DISP_GetDisplayConfig. Can't seem to figure out why.

NvU32 count = 0;
status = NvAPI_DISP_GetDisplayConfig(&count, NULL);
if (status != NVAPI_OK) 
    PrintError(status);
printf("Configs: %i\n", count);
NV_DISPLAYCONFIG_PATH_INFO *configinfos = new NV_DISPLAYCONFIG_PATH_INFO[count];
configinfos[0].version = NV_DISPLAYCONFIG_PATH_INFO_VER;
status = NvAPI_DISP_GetDisplayConfig(&count, configinfos);
if (status != NVAPI_OK) 
    PrintError(status);

On my system, count = 2 after the first call. The notes on NvAPI_DISP_GetDisplayConfig say:

NVAPI_INTERFACE NvAPI_DISP_GetDisplayConfig(
__inout NvU32 * pathInfoCount,
__out_ecount_full_opt *pathInfoCount NV_DISPLAYCONFIG_PATH_INFO * pathInfo
)

DESCRIPTION: This API lets caller retrieve the current global display
configuration.
USAGE: The caller might have to call this three times to fetch all the required
configuration details as follows:
First Pass: Caller should Call NvAPI_DISP_GetDisplayConfig() with pathInfo set
to NULL to fetch pathInfoCount.
Second Pass: Allocate memory for pathInfo with respect to the number of
pathInfoCount(from First Pass) to fetch //! //! targetInfoCount. If
sourceModeInfo is needed allocate memory or it can be initialized to NULL.
Third Pass(Optional, only required if target information is required): Allocate
memory for targetInfo with respect to number of
targetInfoCount(from Second Pass). SUPPORTED OS: Windows Vista and higher

Thanks.

Edit: I've also tried to set configinfos[0].sourceModeInfo = NULL to no avail. I've also tried to iterate over the array to set all .version and .sourceModeInfo to no avail (an example in the docs I saw only set version on the first item in the array)

Answer 1

This should work for you:

NvAPI_Status status = NVAPI_OK;
NvU32 deviceCount = 0;
NV_DISPLAYCONFIG_PATH_INFO_V2 *  pathInfo = NULL;

status = NvAPI_Initialize();
if (status == NVAPI_OK) {
    status = NvAPI_DISP_GetDisplayConfig(&deviceCount, pathInfo);
    if ((status == NVAPI_OK) && (deviceCount > 0)) {
        pathInfo = new NV_DISPLAYCONFIG_PATH_INFO_V2[deviceCount];
        for (int i = 0; i < deviceCount; i++)
        {
            pathInfo[i].targetInfo = 0;
            pathInfo[i].targetInfoCount = 0;
            pathInfo[i].version = NV_DISPLAYCONFIG_PATH_INFO_VER2;
            pathInfo[i].sourceModeInfo = 0;
            pathInfo[i].reserved = 0;
        }

        status = NvAPI_DISP_GetDisplayConfig(&deviceCount, pathInfo);

        if (status == NVAPI_OK) {
            for (int i = 0; i < deviceCount; i++)
            {
                pathInfo[i].sourceModeInfo = new NV_DISPLAYCONFIG_SOURCE_MODE_INFO_V1;
                pathInfo[i].sourceModeInfo->reserved = 0;
                pathInfo[i].targetInfo = new NV_DISPLAYCONFIG_PATH_TARGET_INFO_V2[pathInfo[i].targetInfoCount];
                for (int j = 0; j < pathInfo[i].targetInfoCount; j++) {
                    pathInfo[i].targetInfo[j].details = 0;
                }
            }
        }

        status = NvAPI_DISP_GetDisplayConfig(&deviceCount, pathInfo);

        for (int i = 0; i < deviceCount; i++)
        {
            if (pathInfo[i].sourceModeInfo) delete pathInfo[i].sourceModeInfo;
            if (pathInfo[i].targetInfo) delete [] pathInfo[i].targetInfo;
        }
        delete[] pathInfo;
    }
}

Answer 2

Marcos answer is a more thorough. I believe that the specific problem in your code is that you did not initialize the second pathInfo. So you need to add:

configinfos[1].version = NV_DISPLAYCONFIG_PATH_INFO_VER;

It is also good form to always ininialize your memory. So immediately after allocation you should do:

memset(configinfos, 0, sizeof(NV_DISPLAYCONFIG_PATH_INFO) * count);

or you can individually set the values.

Answer 3

There is a sample named DisplayConfiguration in the sample code that comes with NvAPI that has exploits GetDisplayConfig entirely. Copy pasting the function from DisplayConfiguration.cpp:

NvAPI_Status AllocateAndGetDisplayConfig(NvU32* pathInfoCount, NV_DISPLAYCONFIG_PATH_INFO** pPathInfo)
{
    NvAPI_Status ret;

    // Retrieve the display path information
    NvU32 pathCount                         = 0;
    NV_DISPLAYCONFIG_PATH_INFO *pathInfo    = NULL;

    ret = NvAPI_DISP_GetDisplayConfig(&pathCount, NULL);
    if (ret != NVAPI_OK)    return ret;

    pathInfo = (NV_DISPLAYCONFIG_PATH_INFO*) malloc(pathCount * sizeof(NV_DISPLAYCONFIG_PATH_INFO));
    if (!pathInfo)
    {
        return NVAPI_OUT_OF_MEMORY;
    }

    memset(pathInfo, 0, pathCount * sizeof(NV_DISPLAYCONFIG_PATH_INFO));
    for (NvU32 i = 0; i < pathCount; i++)
    {
        pathInfo[i].version = NV_DISPLAYCONFIG_PATH_INFO_VER;
    }

    // Retrieve the targetInfo counts
    ret = NvAPI_DISP_GetDisplayConfig(&pathCount, pathInfo);
    if (ret != NVAPI_OK)
    {
        return ret;
    }

    for (NvU32 i = 0; i < pathCount; i++)
    {
        // Allocate the source mode info
        pathInfo[i].sourceModeInfo = (NV_DISPLAYCONFIG_SOURCE_MODE_INFO*) malloc(sizeof(NV_DISPLAYCONFIG_SOURCE_MODE_INFO));
        if (pathInfo[i].sourceModeInfo == NULL)
        {
            return NVAPI_OUT_OF_MEMORY;
        }
        memset(pathInfo[i].sourceModeInfo, 0, sizeof(NV_DISPLAYCONFIG_SOURCE_MODE_INFO));

        // Allocate the target array
        pathInfo[i].targetInfo = (NV_DISPLAYCONFIG_PATH_TARGET_INFO*) malloc(pathInfo[i].targetInfoCount * sizeof(NV_DISPLAYCONFIG_PATH_TARGET_INFO));
        if (pathInfo[i].targetInfo == NULL)
        {
            return NVAPI_OUT_OF_MEMORY;
        }
        // Allocate the target details
        memset(pathInfo[i].targetInfo, 0, pathInfo[i].targetInfoCount * sizeof(NV_DISPLAYCONFIG_PATH_TARGET_INFO));
        for (NvU32 j = 0 ; j < pathInfo[i].targetInfoCount ; j++)
        {
            pathInfo[i].targetInfo[j].details = (NV_DISPLAYCONFIG_PATH_ADVANCED_TARGET_INFO*) malloc(sizeof(NV_DISPLAYCONFIG_PATH_ADVANCED_TARGET_INFO));    
            memset(pathInfo[i].targetInfo[j].details, 0, sizeof(NV_DISPLAYCONFIG_PATH_ADVANCED_TARGET_INFO));
            pathInfo[i].targetInfo[j].details->version = NV_DISPLAYCONFIG_PATH_ADVANCED_TARGET_INFO_VER;
        }
    }

    // Retrieve the full path info
    ret = NvAPI_DISP_GetDisplayConfig(&pathCount, pathInfo);
    if (ret != NVAPI_OK)    
    {
        return ret;
    }

    *pathInfoCount = pathCount;
    *pPathInfo = pathInfo;
    return NVAPI_OK;
}

Now this function can be used as easily as:

NV_DISPLAYCONFIG_PATH_INFO *pathInfo = NULL;
NvU32 pathCount = 0;
_allocateAndGetDisplayConfig(&pathCount, &pathInfo);
// Do whatever you need with the queried display data here