我下面的代码从 USB 设备（例如鼠标）获取 4 位数据。一切正常，除了当我运行代码和结束时我的鼠标停止工作。如果我再次运行我的代码，那么它会给出错误或不希望的或意外的结果。我必须拔下设备并再次运行我的代码，然后才能得到预期的答案。
什么可能导致这种情况，我该如何解决？
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <libusb-1.0/libusb.h>
//=========================================================================
// This program detects usb and print out their details and reads data
//=========================================================================
int main (int argc, char *argv)
{
libusb_device **devList = NULL;
libusb_device *devPtr = NULL;
libusb_device_handle *devHandle = NULL;
libusb_context *ctx = NULL; //a libusb session
struct libusb_device_descriptor devDesc;
struct libusb_config_descriptor *configDesc ;
unsigned char strDesc[256];
ssize_t numUsbDevs = 0; // pre-initialized scalars
ssize_t idx = 0;
int retVal = 0;
//========================================================================
// test out the libusb functions
//========================================================================
printf ("*************************\n USB Detection Program:\n*************************\n");
retVal = libusb_init (&ctx);
if(retVal < 0) {
printf ("%d",retVal," Init Error "); //there was an error
return 1;
}
//========================================================================
// Get the list of USB devices visible to the system.
//========================================================================
numUsbDevs = libusb_get_device_list (ctx, &devList); //Return no.of USB Devices
//========================================================================
// Loop through the list, looking for the device
//========================================================================
while (idx < numUsbDevs)
{
printf ("\n\n[%d]\n", idx+1);
//=====================================================================
// Get next device pointer out of the list, use it to open the device.
//=====================================================================
devPtr = devList[idx];
retVal = libusb_open (devPtr, &devHandle);
if (retVal != LIBUSB_SUCCESS)
break;
//=====================================================================
// Get the device descriptor for this device.
//=====================================================================
retVal = libusb_get_device_descriptor (devPtr, &devDesc);
if (retVal != LIBUSB_SUCCESS)
break;
//=====================================================================
// Get the string associated with iManufacturer index.
//=====================================================================
printf ("iManufacturer = %d", devDesc.iManufacturer);
if (devDesc.iManufacturer > 0)
{
retVal = libusb_get_string_descriptor_ascii
(devHandle, devDesc.iManufacturer, strDesc, 256);
if (retVal < 0)
break;
printf (" string = %s", strDesc);
}
//========================================================================
// Get string associated with iProduct index.
//========================================================================
printf (" \niProduct = %d", devDesc.iProduct);
if (devDesc.iProduct > 0)
{
retVal = libusb_get_string_descriptor_ascii
(devHandle, devDesc.iProduct, strDesc, 256);
if (retVal < 0)
break;
printf (" string = %s", strDesc);
}
//==================================================================
// Get string associated with iSerialNumber index.
//==================================================================
printf (" \niSerialNumber = %d", devDesc.iSerialNumber);
if (devDesc.iSerialNumber > 0)
{
retVal = libusb_get_string_descriptor_ascii
(devHandle, devDesc.iSerialNumber, strDesc, 256);
if (retVal < 0)
break;
printf (" string = %s", strDesc);
}
//==================================================================
// Print product id and Vendor id and
//==================================================================
printf (" \nProductid = %d", devDesc.idProduct);
printf (" \nVendorid = %d", devDesc.idVendor);
//========================================================================
// Close and try next one.
//========================================================================
libusb_close (devHandle);
devHandle = NULL;
idx++;
//========================================================================
// Selection of device by user
//========================================================================
if(idx==numUsbDevs)
{ printf("\n\nselect the device : ");
scanf("%d",&idx);
if(idx > numUsbDevs)
{printf("Invalid input, Quitting.............");
break; }
devPtr = devList[idx-1];
retVal = libusb_open (devPtr, &devHandle);
if (retVal != LIBUSB_SUCCESS)
break;
retVal = libusb_get_device_descriptor (devPtr, &devDesc);
if (retVal != LIBUSB_SUCCESS)
break;
printf (" \nProductid = %d", devDesc.idProduct);
printf (" \nVendorid = %d", devDesc.idVendor);
retVal = libusb_get_config_descriptor(devPtr, 0, &configDesc);
printf( "\nNumber of Interfaces:%d", (int)configDesc->bNumInterfaces);
const struct libusb_interface *inter;
const struct libusb_interface_descriptor *interdesc;
const struct libusb_endpoint_descriptor *epdesc;
int i,j,k ;
for ( i = 0; i < (int)configDesc->bNumInterfaces; i++) {
inter = &configDesc->interface[i];
printf( "\nNumber of alt settings: %d " , inter->num_altsetting);
for ( j = 0; j < inter->num_altsetting; j++) {
interdesc = &inter->altsetting[j];
printf( "\nInterface number: %d" ,(int)interdesc->bInterfaceNumber);
printf( "\nNumber of endpoints: %d" , (int)interdesc->bNumEndpoints);
for ( k = 0; k < (int)interdesc->bNumEndpoints; k++) {
epdesc = &interdesc->endpoint[k];
printf("\n\nDescriptor type:%d " ,(int)epdesc->bDescriptorType);
printf("\nEP Address : %d" ,(int)epdesc->bEndpointAddress);
}
}
}
//========================================================================
// Reading Data
//========================================================================
unsigned char data[4]; //data to read
// data[0]='a';data[1]='b';data[2]='c';data[3]='d'; //some dummy values
if(libusb_kernel_driver_active(devHandle, 0) == 1) { //find out if kernel driver is attached
printf("\nKernel Driver Active\n");
if(libusb_detach_kernel_driver(devHandle, 0) == 0) //detach it
printf("Kernel Driver Detached!");
}
int r; //for return values
r = libusb_claim_interface(devHandle, 0); //claim interface of device
if(r < 0) {
printf("\nCannot Claim Interface %d",r);
return 1;
}
printf("\nClaimed Interface\n");
int actual_length; //used to find out how many bytes were written
r = libusb_bulk_transfer(devHandle,129, data, sizeof(data), &actual_length, 0);
printf("r is %d\n",r);
FILE *fp;
fp=fopen("test.txt","w");
if (r == 0 && actual_length == sizeof(data)) {
for(i=0; i<sizeof(data);i++)
{
fprintf(fp,"%u\t",data[i]);
printf("%u\t",data[i]);
}
// results of the transaction can now be found in the data buffer
// parse them here and report button press
}
else {
error();
}
r = libusb_release_interface(devHandle, 0); //release the claimed interface
if(r!=0) {
printf("\nCannot Release Interface");
return 1;
}
printf("\nReleased Interface");
idx=numUsbDevs +2; //to exit if statement
}
} // end of while loop
if (devHandle != NULL)
{
//========================================================================
// Close device if left open due to break out of loop on error.
//========================================================================
libusb_close (devHandle);
}
libusb_exit (ctx); //close the session
printf ("\n*************************\n Done\n*************************\n");
return 0;
}
//==========================================
// EOF
//==========================================