Improper output using libusb

问题

I have made a program using libusb. I doubt if the output is correct as all the entries show the same vendor and product id. Following is the code:

#include <stdio.h>
#include <stdlib.h>
#include <libusb-1.0/libusb.h>

void print_devices(libusb_device *dev)
{
    struct libusb_device_descriptor desc;
    struct libusb_config_descriptor *config;

    const struct libusb_interface *inter;
    const struct libusb_interface_descriptor *interdesc;
    const struct libusb_endpoint_descriptor *endpointdesc;

    int ret;
    int i,j,k;

    if(ret<0)
    {   
        fprintf(stderr,"error in getting device descriptor\n");
        return;
    }

    printf("Number of possible configs is %d\n",desc.bNumConfigurations);
    printf("Vendor: %d\n",desc.idVendor);
    printf("Product ID: %d\n",desc.idProduct);

    libusb_get_config_descriptor(dev, 0, &config);

    printf("Interface: %d\n", config->bNumInterfaces);
    printf("\n\n"); 
}


int main(int argc,char *argv[])
{
    libusb_device **devs;
    libusb_context *context = NULL;

    size_t list;
    size_t i;

    int ret,temp;

    ret = libusb_init(&context);

    if(ret < 0)
    {
        perror("libusb_init");
        exit(1);
    }

    list = libusb_get_device_list(context, &devs);

    if(list < 0)
    {
        fprintf(stderr, "Error in getting device list\n");
        libusb_free_device_list(devs, 1);
        libusb_exit(context);
        exit(1);
    }

    temp=(int)list;
    printf("\n%d devices found\n\n",temp);

    for(i=0;i<temp;i++)
    {
        //print devices
        print_devices(devs[i]);
    }

    libusb_free_device_list(devs, 1);
    libusb_exit(context);

    return 0;
}

and this is my output:

anubhav@anubhav-Inspiron-3421:~/Desktop/usb$ ./usbtest

9 devices found

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 2

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 4

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

Number of possible configs is 103
Vendor: 0
Product ID: 0
Interface: 1

this is what lsusb shows:

anubhav@anubhav-Inspiron-3421:~/Desktop/usb$ lsusb
Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 001 Device 004: ID 064e:812c Suyin Corp. 
Bus 001 Device 007: ID 0a5c:21d7 Broadcom Corp. BCM43142 Bluetooth 4.0
Bus 001 Device 003: ID 0bda:0129 Realtek Semiconductor Corp. RTS5129 Card Reader Controller
Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Need help to locate the error(if any).

回答1:

A line must have been accidentally skipped somewhere... I suggest you add the following line, otherwise ret is unitialized :

int ret;
int i,j,k;

ret = libusb_get_device_descriptor(dev, &desc);//this line !
if(ret<0)
{   
    fprintf(stderr,"error in getting device descriptor\n");
    return;
}

To compare the output to the one of lsusb, change for %x to print idVendor and idProduct using hexadecimal format.

printf("Vendor: %x\n",desc.idVendor);
printf("Product ID: %x\n",desc.idProduct);

The following question libusb semi-working, but libusb_device_descriptor undeclared? was helpful to find the missing line. And this one helped me linking libusb Libusb undefined reference to it advices to compile by gcc main.c -o main -lusb-1.0.

来源：https://stackoverflow.com/questions/29083184/improper-output-using-libusb

标签

Linux

libusb