Skip to main content

Generic Swap without using template

The idea behind this was, I wanted to write a function that will take two parameters of the same type as a parameter and then it will swap them. It is a kind of generic swap but without the use of a C++ template. So the best way of doing it using "void *" as a parameter. As we know "void *" represents any arbitrary type that actually eases my job of writing a generic swap function. So, the function signature can be like below: 
void swap(void *arg1, void *arg2);
"void *" points to the starting address of the arbitrary location in the memory, irrespective of the bit pattern. Try to write the function like the below: 
void swap(void *arg1, void *arg2)
{
    void temp = *arg1;
    arg1 = *arg2;
    *arg = temp;
}
Oops, this is full of errors. 
1. We can't declare a variable of type "void".
2. "void *" can't be dereferenced. 
3. We also interested in swapping values. 
   So, number of bytes making up the values to 
   be passed as parameter.
Here is the functional version of the swap function. 
void swap(void *arg1, void *arg2, int size)
{
    char *buffer = new char[size];
    memcpy(buffer, arg1, size);
    memcpy(arg1, arg2, size);
    memcpy(arg2, buffer, size);
    delete []buffer;
}
How do we going to use this function from our client code? We can do it like below: (I have used vc++, 2005) 
int _tmain(int argc, _TCHAR* argv[])
{
 int one = 1;
 int two = 2;
 swap(&one, &two, sizeof(int *));

 cout << one << ":" << two << endl;

 char *n = _strdup("World");
 char *t = _strdup("Hello");
 swap(&n, &t, sizeof(char *));

 cout << n << ":" << t << endl;
 return 0;
}
and the output is like below: Please remember to pass the same type of parameter always as above. Avoid trying to pass arguments like: 
    int one = 1;
    short two = 2;
    swap(&one, &two, sizeof(short *));
The advantage of this over the template is the same assembly code being used for multiple calls as opposed to a template, which creates a separate copy for each call.

Comments

Post a Comment

Popular posts from this blog

Reversing char array without splitting the array to tokens

 I was reading about strdup, a C++ function and suddenly an idea came to my mind if this can be leveraged to aid in reversing a character array without splitting the array into words and reconstructing it again by placing spaces and removing trailing spaces. Again, I wanted an array to be passed as a function argument and an array size to be passed implicitly with the array to the function. Assumed, a well-formed char array has been passed into the function. No malformed array checking is done inside the function. So, the function signature and definition are like below: Below is the call from the client code to reverse the array without splitting tokens and reconstructing it. Finally, copy the reversed array to the destination.  For GNU C++, we should use strdup instead _strdup . On run, we get the following output: Demo code
Post a Comment
Read more

Close a Window Application from another application.

 This is just a demo application code to show how the WM_CLOSE message can be sent to the target process which has a titled window to close the application. To achieve this, either we can use SendMessage or PostMessage APIs to send required Windows messages to the target application. Though both the APIs are dispatching WM_XXXXX message to target application two APIs has some differences, these are as below: 1. SendMessage () call is a blocking call but PostMessage is a non-blocking call(Asynchronous) 2. SendMessage() APIs return type is LRESULT (LONG_PTR) but PostMessage() APIs return type is BOOL(typedef int). In Short, SendMessage () APIs return type depends on what message has been sent to the Windowed target process. For the other one, it's always a non-zero value, which indicates the message has been successfully placed on the target process message queue. Now let's see how can I close a target windowed application "Solitaire & Casual Games" from my custom-
Post a Comment
Read more

XOR (Exclusive OR) for branchless coding

The following example shows the array reversing using the  XOR operator . No need to take any additional variable to reverse the array.   int main(int argc, _TCHAR* argv[]) { char str[] = "I AM STUDENT"; int length = strlen(str); for(int i = 0; i < ((length/2)); i++) { str[i] ^= str[length - (1+i)]; str[length - (1+i)] ^= str[i]; str[i] ^= str[length - (1+i)]; } cout << str << endl; return 0; } The above example is one of the uses of XOR but XOR comes in handy when we can do branchless coding  methods like butterfly switch etc. Sometimes this is very effective in speeding up the execution.  Let's see one of the uses of XOR in branchless coding. I am taking a simple example of Y = | X |.  Yes, I am generating abs of a supplied number. So, my function signature/definition in C++ looks like below: int absoluteBranch( int x) {     if (x < 0 ) {         return -x;     }     else {         retur
1 comment
Read more