基于qt的上位机与下位机usb通信，无法读取下位机的数据

基于qt的上位机与下位机usb通信，无法读取下位机的数据！
现在可以读取usb设备信息，有用qt写过usb通信上位机的吗？现在卡在不知道怎么读取下位机数据！网上关于这块的信息好少
这是.cpp代码，用的是libusb-1.0的库

#include <QDebug>
#include <stdio.h>
#include "libusb.h"

int verbose = 0;

static void print_endpoint_comp(const struct libusb_ss_endpoint_companion_descriptor *ep_comp)
{
    printf("      USB 3.0 Endpoint Companion:\n");
    printf("        bMaxBurst:           %u\n", ep_comp->bMaxBurst);
    printf("        bmAttributes:        %02xh\n", ep_comp->bmAttributes);
    printf("        wBytesPerInterval:   %u\n", ep_comp->wBytesPerInterval);
}

static void print_endpoint(const struct libusb_endpoint_descriptor *endpoint)
{
    int i, ret;

    printf("      Endpoint:\n");
    printf("        bEndpointAddress:    %02xh\n", endpoint->bEndpointAddress);
    printf("        bmAttributes:        %02xh\n", endpoint->bmAttributes);
    printf("        wMaxPacketSize:      %u\n", endpoint->wMaxPacketSize);
    printf("        bInterval:           %u\n", endpoint->bInterval);
    printf("        bRefresh:            %u\n", endpoint->bRefresh);
    printf("        bSynchAddress:       %u\n", endpoint->bSynchAddress);

    for (i = 0; i < endpoint->extra_length;) {
        if (LIBUSB_DT_SS_ENDPOINT_COMPANION == endpoint->extra[i + 1]) {
            struct libusb_ss_endpoint_companion_descriptor *ep_comp;

            ret = libusb_get_ss_endpoint_companion_descriptor(NULL, endpoint, &ep_comp);
            if (LIBUSB_SUCCESS != ret)
                continue;

            print_endpoint_comp(ep_comp);

            libusb_free_ss_endpoint_companion_descriptor(ep_comp);
        }

        i += endpoint->extra[i];
    }
}

static void print_altsetting(const struct libusb_interface_descriptor *interface)
{
    uint8_t i;

    printf("    Interface:\n");
    printf("      bInterfaceNumber:      %u\n", interface->bInterfaceNumber);
    printf("      bAlternateSetting:     %u\n", interface->bAlternateSetting);
    printf("      bNumEndpoints:         %u\n", interface->bNumEndpoints);
    printf("      bInterfaceClass:       %u\n", interface->bInterfaceClass);
    printf("      bInterfaceSubClass:    %u\n", interface->bInterfaceSubClass);
    printf("      bInterfaceProtocol:    %u\n", interface->bInterfaceProtocol);
    printf("      iInterface:            %u\n", interface->iInterface);

    for (i = 0; i < interface->bNumEndpoints; i++)
        print_endpoint(&interface->endpoint[i]);
}

static void print_2_0_ext_cap(struct libusb_usb_2_0_extension_descriptor *usb_2_0_ext_cap)
{
    printf("    USB 2.0 Extension Capabilities:\n");
    printf("      bDevCapabilityType:    %u\n", usb_2_0_ext_cap->bDevCapabilityType);
    printf("      bmAttributes:          %08xh\n", usb_2_0_ext_cap->bmAttributes);
}

static void print_ss_usb_cap(struct libusb_ss_usb_device_capability_descriptor *ss_usb_cap)
{
    printf("    USB 3.0 Capabilities:\n");
    printf("      bDevCapabilityType:    %u\n", ss_usb_cap->bDevCapabilityType);
    printf("      bmAttributes:          %02xh\n", ss_usb_cap->bmAttributes);
    printf("      wSpeedSupported:       %u\n", ss_usb_cap->wSpeedSupported);
    printf("      bFunctionalitySupport: %u\n", ss_usb_cap->bFunctionalitySupport);
    printf("      bU1devExitLat:         %u\n", ss_usb_cap->bU1DevExitLat);
    printf("      bU2devExitLat:         %u\n", ss_usb_cap->bU2DevExitLat);
}

static void print_bos(libusb_device_handle *handle)
{
    struct libusb_bos_descriptor *bos;
    uint8_t i;
    int ret;

    ret = libusb_get_bos_descriptor(handle, &bos);
    if (ret < 0)
        return;

    printf("  Binary Object Store (BOS):\n");
    printf("    wTotalLength:            %u\n", bos->wTotalLength);
    printf("    bNumDeviceCaps:          %u\n", bos->bNumDeviceCaps);

    for (i = 0; i < bos->bNumDeviceCaps; i++) {
        struct libusb_bos_dev_capability_descriptor *dev_cap = bos->dev_capability[i];

        if (dev_cap->bDevCapabilityType == LIBUSB_BT_USB_2_0_EXTENSION) {
            struct libusb_usb_2_0_extension_descriptor *usb_2_0_extension;

            ret = libusb_get_usb_2_0_extension_descriptor(NULL, dev_cap, &usb_2_0_extension);
            if (ret < 0)
                return;

            print_2_0_ext_cap(usb_2_0_extension);
            libusb_free_usb_2_0_extension_descriptor(usb_2_0_extension);
        } else if (dev_cap->bDevCapabilityType == LIBUSB_BT_SS_USB_DEVICE_CAPABILITY) {
            struct libusb_ss_usb_device_capability_descriptor *ss_dev_cap;

            ret = libusb_get_ss_usb_device_capability_descriptor(NULL, dev_cap, &ss_dev_cap);
            if (ret < 0)
                return;

            print_ss_usb_cap(ss_dev_cap);
            libusb_free_ss_usb_device_capability_descriptor(ss_dev_cap);
        }
    }

    libusb_free_bos_descriptor(bos);
}

static void print_interface(const struct libusb_interface *interface)
{
    int i;

    for (i = 0; i < interface->num_altsetting; i++)
        print_altsetting(&interface->altsetting[i]);
}

static void print_configuration(struct libusb_config_descriptor *config)
{
    uint8_t i;

    printf("  Configuration:\n");
    printf("    wTotalLength:            %u\n", config->wTotalLength);
    printf("    bNumInterfaces:          %u\n", config->bNumInterfaces);
    printf("    bConfigurationValue:     %u\n", config->bConfigurationValue);
    printf("    iConfiguration:          %u\n", config->iConfiguration);
    printf("    bmAttributes:            %02xh\n", config->bmAttributes);
    printf("    MaxPower:                %u\n", config->MaxPower);

    for (i = 0; i < config->bNumInterfaces; i++)
        print_interface(&config->interface[i]);
}

void print_device(libusb_device *dev, libusb_device_handle *handle)
{
    struct libusb_device_descriptor desc;
    unsigned char string[256];
    const char *speed;
    int ret;
    uint8_t i;

    switch (libusb_get_device_speed(dev)) {
    case LIBUSB_SPEED_LOW:        speed = "1.5M"; break;
    case LIBUSB_SPEED_FULL:        speed = "12M"; break;
    case LIBUSB_SPEED_HIGH:        speed = "480M"; break;
    case LIBUSB_SPEED_SUPER:    speed = "5G"; break;
    case LIBUSB_SPEED_SUPER_PLUS:    speed = "10G"; break;
    default:            speed = "Unknown";
    }

    ret = libusb_get_device_descriptor(dev, &desc);
    if (ret < 0) {
        fprintf(stderr, "failed to get device descriptor");
        return;
    }

    printf("Dev (bus %u, device %u): %04X - %04X speed: %s\n",
           libusb_get_bus_number(dev), libusb_get_device_address(dev),
           desc.idVendor, desc.idProduct, speed);

    if (!handle)
        libusb_open(dev, &handle);

    //之前版本程序代码
    if (handle)
    {
        if (desc.iManufacturer) {
            ret = libusb_get_string_descriptor_ascii(handle, desc.iManufacturer, string, sizeof(string));
            if (ret > 0)
                printf("  Manufacturer:              %s\n", (char *)string);
        }

        if (desc.iProduct) {
            ret = libusb_get_string_descriptor_ascii(handle, desc.iProduct, string, sizeof(string));
            if (ret > 0)
                printf("  Product:                   %s\n",  (char *)string);
        }

        if (desc.iSerialNumber && verbose) {
            ret = libusb_get_string_descriptor_ascii(handle, desc.iSerialNumber, string, sizeof(string));
            if (ret > 0)
                printf("  Serial Number:             %s\n", (char *)string);
        }
    }

    if (verbose) {
        for (i = 0; i < desc.bNumConfigurations; i++) {
            struct libusb_config_descriptor *config;

            ret = libusb_get_config_descriptor(dev, i, &config);
            if (LIBUSB_SUCCESS != ret) {
                printf("  Couldn't retrieve descriptors\n");
                continue;
            }

            print_configuration(config);

            libusb_free_config_descriptor(config);
        }

        if (handle && desc.bcdUSB >= 0x0201)
            print_bos(handle);
    }

    if (handle)
        libusb_close(handle);
}