Windows VC++ 2010 link error _main - visual-c++

Question

I was trying to poll available devices on a Windows machine by this code example from Microsoft. But there are link errors that relates to _main().
#include <stdio.h>
#include <windows.h>
#include <setupapi.h>
#include <devguid.h>
#include <regstr.h>
int main( int argc, char *argv[ ], char *envp[ ] )
{
HDEVINFO hDevInfo;
SP_DEVINFO_DATA DeviceInfoData;
DWORD i;
// Create a HDEVINFO with all present devices.
hDevInfo = SetupDiGetClassDevs(NULL,
0, // Enumerator
0,
DIGCF_PRESENT | DIGCF_ALLCLASSES );
if (hDevInfo == INVALID_HANDLE_VALUE)
{
// Insert error handling here.
return 1;
}
// Enumerate through all devices in Set.
DeviceInfoData.cbSize = sizeof(SP_DEVINFO_DATA);
for (i=0;SetupDiEnumDeviceInfo(hDevInfo,i,
&DeviceInfoData);i++)
{
DWORD DataT;
LPTSTR buffer = NULL;
DWORD buffersize = 0;
//
// Call function with null to begin with,
// then use the returned buffer size (doubled)
// to Alloc the buffer. Keep calling until
// success or an unknown failure.
//
// Double the returned buffersize to correct
// for underlying legacy CM functions that
// return an incorrect buffersize value on
// DBCS/MBCS systems.
//
while (!SetupDiGetDeviceRegistryProperty(
hDevInfo,
&DeviceInfoData,
SPDRP_DEVICEDESC,
&DataT,
(PBYTE)buffer,
buffersize,
&buffersize))
{
if (GetLastError() ==
ERROR_INSUFFICIENT_BUFFER)
{
// Change the buffer size.
if (buffer) LocalFree(buffer);
// Double the size to avoid problems on
// W2k MBCS systems per KB 888609.
buffer = LocalAlloc(LPTR,buffersize * 2);
}
else
{
// Insert error handling here.
break;
}
}
printf("Result:[%s]\n",buffer);
if (buffer) LocalFree(buffer);
}
if ( GetLastError()!=NO_ERROR &&
GetLastError()!=ERROR_NO_MORE_ITEMS )
{
// Insert error handling here.
return 1;
}
// Cleanup
SetupDiDestroyDeviceInfoList(hDevInfo);
return 0;
}
For some reasons, there are link errors:
1>device.obj : error LNK2019: unresolved external symbol __imp__SetupDiDestroyDeviceInfoList#4 referenced in function _main
1>device.obj : error LNK2019: unresolved external symbol __imp__SetupDiGetDeviceRegistryPropertyW#28 referenced in function _main
1>device.obj : error LNK2019: unresolved external symbol __imp__SetupDiEnumDeviceInfo#12 referenced in function _main
1>device.obj : error LNK2019: unresolved external symbol __imp__SetupDiGetClassDevsW#16 referenced in function _main
1>c:\users\visual studio 2010\Projects\usb\Debug\usb.exe : fatal error LNK1120: 4 unresolved externals
What they are about? There is no _main() at all.

Answer 1

First thing first, the linker errors are not about missing main, but about other functions that are referenced (called) from main.
The functions you mentioned in linker errors are from library: Setupapi.lib, and you need to include it in Linker settings (Input) of your project.
Why did it worked on VS re-open?
Probably simply because you changed the configuration (by mistake). For example from Win32 to x64, and/or from Debug to Release (or any combination) of these. The other configuration didn't have reference to this library added.