Creating application with a single instance in C and VB .NET


Most of us prefer to have single instances application to make it look professional or probably some other personal reason especially making malicious applications too.  Here is the source code for the 2 languages that has been mentioned.

C

#include <windows.h>

int main()
{
	char *mutex = "some name here";

	HANDLE hMutex = OpenMutex(MUTEX_ALL_ACCESS, FALSE, mutex);
	if(hMutex == NULL)
	{
		hMutex = CreateMutex(NULL, FALSE, mutex);
	}
	else
	{
		MessageBox(0, "Instance Exists!", 0, 0);
		return 0;
	}

	return 0;
}

VB .NET

Function PrevInstance() As Boolean
	If UBound(Diagnostics.Process.GetProcessesByName(Diagnostics.Process.GetCurrentProcess.ProcessName)) > 0 Then
            Return True
        Else
            Return False
        End If
End Function

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
	If PrevInstance() = True Then
            MsgBox("Instance Exists!")
            End
        End If
End Sub
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