/CLRSUPPORTLASTERROR (Preserve Last Error Code for PInvoke Calls)

  • Article

/CLRSUPPORTLASTERROR, which is on by default, preserves the last error code of functions called through the P/Invoke mechanism, which allows you to call native functions in DLLS, from code compiled with /clr.

Syntax

/CLRSUPPORTLASTERROR
/CLRSUPPORTLASTERROR:NO
/CLRSUPPORTLASTERROR:SYSTEMDLL

Remarks

Preserving the last error code implies a decrease in performance. If you don't want to incur the performance cost of preserving the last error code, link by using /CLRSUPPORTLASTERROR:NO.

You can minimize the performance penalty by linking with /CLRSUPPORTLASTERROR:SYSTEMDLL, which only preserves the last error code for functions in system DLLs.

Note

Preserving the last error isn't supported for unmanaged functions that are consumed by CLR code in the same module.

To set this linker option in the Visual Studio development environment

  1. Open the Property Pages dialog box for the project. For more information, see Set compiler and build properties.

  2. Select the Configuration Properties > Linker > Advanced property page.

  3. Modify the Preserve Last Error Code for PInvoke Calls property. Choose OK or Apply to save your changes.

To set this linker option programmatically

Examples

The following sample defines a native DLL with one exported function that modifies last error.

// CLRSUPPORTLASTERROR_dll.cpp
// compile with: /LD
#include <windows.h>
#include <math.h>

#pragma unmanaged
__declspec(dllexport) double MySqrt(__int64 n) {
   SetLastError(DWORD(-1));
   return sqrt(double(n));
}

The following sample consumes the DLL, demonstrating how to use /CLRSUPPORTLASTERROR.

// CLRSUPPORTLASTERROR_client.cpp
// compile with: /clr CLRSUPPORTLASTERROR_dll.lib /link /clrsupportlasterror:systemdll
// processor: x86
#include <windows.h>
#include <wininet.h>
#include <stdio.h>
#include <math.h>

#pragma comment(lib, "wininet.lib")

double MySqrt(__int64 n);

#pragma managed
int main() {
   double   d = 0.0;
   __int64 n = 65;
   HANDLE  hGroup = NULL;
   GROUPID groupID;
   DWORD   dwSet = 127, dwGet = 37;

   SetLastError(dwSet);
   d = MySqrt(n);
   dwGet = GetLastError();

   if (dwGet == DWORD(-1))
      printf_s("GetLastError for application call succeeded (%d).\n",
             dwGet);
   else
      printf_s("GetLastError for application call failed (%d).\n",
             dwGet);

   hGroup = FindFirstUrlCacheGroup(0, CACHEGROUP_SEARCH_ALL,
                           0, 0, &groupID, 0);
   dwGet = GetLastError();
   if (dwGet == 183)
      printf_s("GetLastError for system call succeeded (%d).\n",
             dwGet);
   else
      printf_s("GetLastError for system call failed (%d).\n",
             dwGet);
}

GetLastError for application call failed (127).
GetLastError for system call succeeded (183).

See also

MSVC linker reference
MSVC linker options