八进制常量错误（libusb）

Question

I am running Ubuntu 12.04 compiling a c++ file which has the following code

#include <iostream>
#include <libusb-1.0/libusb.h>

using namespace std;

int main(){
    //pointer to pointer of device used to retrieve a list of devices
    libusb_device **devs;
    libusb_device_handle *dev_handle; //a device handle
    libusb_context *ctx = NULL; //A LIBUSB session
    int r;// for return values
    ssize_t cnt; //holding number of devices in list
    r = libusb_init(&ctx); // initialize the library for the session we just declared

    if(r < 0){
        cout <<"init error "<<r<< endl;
        return 1;
    }

    libusb_set_debug(ctx, 3); // set verbosity level to 3, as suggested in the documentation
    cnt = libusb_get_device_list(ctx, &devs); //get the list of devices

    if (cnt < 0) {
        cout <<"Get Device Error "<< endl; // there was an error
        return 1;
    }

    cout << cnt <<" Device in list " << endl;
    //dev_handle = libusb_open_device_with_vid_pid(ctx, 0951, 1689); // these are vendor id and product id   //simon's usb(duracell)1516:1213
    dev_handle = libusb_open_device_with_vid_pid(ctx, 0951, 1689); //these are vendorID and productID I found for my usb device

    if (dev_handle == NULL){
        cout <<"Cannot open device "<< endl;
    }else{
        cout << "Device opened" << endl;
    }

    libusb_free_device_list(devs, 1);// free the list unref the devices in it

    unsigned char *data = new unsigned char[4];//data to write
    data[0] = 'a'; data[1] = 'b'; data[2] = 'c'; data[3] = 'd';//some dummy values

    int actual; //used to find how many bytes were written

    if (libusb_kernel_driver_active(dev_handle, 0) == 1){// findout if kernal driver attached
        cout << "Kernal Driver Active" << endl;
        if (libusb_detach_kernel_driver(dev_handle, 0) == 0 ){  //detach it
            cout<< "Kernal Driver Detached" << endl;
        }
    }

    r = libusb_claim_interface(dev_handle, 0);// claim interface 0 (the first) of devices

    if(r < 0){
        cout <<"Cannot claim interface "<<endl;
        return 1;
    }

    cout <<"Claimed interface "<<endl;

    cout<<"data->"<<data<<"<-"<<endl; // just to see the data we want to write : abcd
    cout<<"Writing data..."<<endl;

    r = libusb_bulk_transfer(dev_handle, (2 | LIBUSB_ENDPOINT_OUT), data, 4, &actual, 0);//my device's out endpoint was 2, found withe trial - the device had two endpoints: 2 and 129

    if(r == 0 && actual == 4){  // we wrote 4 bytes successfully
        cout<<"Writing successfull"<<endl;
    }else{
        cout<<"write error"<<endl;
    }

    r = libusb_release_interface(dev_handle, 0); // release the claimed interface

    if(r!=0) {
        cout<<"Cannot Release Interface"<<endl;
        return 1;
    }
    cout<<"Released interface"<<endl;
    libusb_close(dev_handle); // close the device we opened
    libusb_exit(ctx); // need to be called to end the

    delete[] data;// delete the allocated memory for data
    return 0;
}

but when i compile the above code using the following command line (these are the product id and vendor id of my usb)

dev_handle = libusb_open_device_with_vid_pid(ctx, 0951, 1689);

the compiler throws the following error

transfer_data_libusb.cpp:30:55: error: invalid digit "9" in octal constant

Someone had adviced me to remove the leading zero ie ("951" instead of "0951") but when i do that, the file gets compiled successfully, but when i rnu the compiled version this throws the following error

7 Device in list 
Cannot open device 
Segmentation fault (core dumped)

dont know what should I do can you please help btw i use the following command to compile the above code

g++ transfer_data_libusb.cpp $(pkg-config --libs libusb-1.0) -o transfer_data_libusb

thank you very much for you time

Answer 1

Your number is probably in hexadecimal. Use:

0x951

instead of your 0951 .

And:

0x1689

instead of your 1689 .

If you see the other numbers in (I assume it is your product):

http://usbspeed.nirsoft.net/?g=32gb

they have a to f characters, so it means the format should be hexadecimal.

Answer 2

When your call fails

dev_handle = libusb_open_device_with_vid_pid(ctx, 0951, 1689); 

dev_handle will be NULL.

if (dev_handle == NULL){
    cout <<"Cannot open device "<< endl;
    //treat error here and quit

You need to stop operating on dev_handle then.