Skip to main content

strcpy / strcmp implementation

 In C/C++ we have a library function called strcpy to copy the source character array to the destination character array. The C++ function details have been documented here. Today I tried to implement it in my own way. I have put forth a few conditions to implement this function, which are described below.

1. I don't want to pass the size of arrays as function parameters. I mean, the parameter gets passed implicitly
2. I don't want the program shall compile if any of the array sizes or both array sizes are zero or one.
3. There shall be no operation if source and destination arrays are the same.
4. No overflow happens if the destination array size is smaller than the source.
5. The destination array must be null-terminated after a successful copy.


Below is the client code to test the implementation:
int main()
{
// Case 1: Source and destination arrays are of the same size
char src[] = "Hello World";
char dest[12] = {}; // n - 1 chars will be copied and the last one will be '\0'

_strcpy(dest, src);
std::cout << "After the copy: " << dest << "\n";

for (int i = 0; i < 12; ++i) {
if (dest[i] == '\0') {
std::cout << "Null termination present..." << "\n";
}
}

// Case 2: Source and destination arrays are of different sizes, destination array size is smaller
char dest_1[6] = {};
_strcpy(dest_1, src);
std::cout << "After the copy: " << dest_1 << "\n";

for (int i = 0; i < 6; ++i) {
if (dest_1[i] == '\0') {
std::cout << "Null termination present..." << "\n";
}
}

// Case 3: source and destination arrays are of different sizes, 
// destination array size is the smallest permissible size...
char dest_2[2] = {};
_strcpy(dest_2, src);
std::cout << "After the copy: " << dest_2 << "\n";

for (int i = 0; i < 2; ++i) {
if (dest_1[i] == '\0') {
std::cout << "Null termination present..." << "\n";
}
}

// Case 4: Src to Src copy, results in no operation just return;
_strcpy(src, src);

// Case 5: The destination array size is bigger than the source array size
char dest_10[100] = {};
_strcpy(dest_10, src);
std::cout << "After the copy: " << dest_10 << "\n";

for (int i = 0; i < 100; ++i) {
if (dest_1[i] == '\0') {
std::cout << "Null termination present..." << "\n";
break;
}
}

// Case 6: Logical error case, source and destination interchanged while calling the API
char dest_11[12] = {};
_strcpy(src, dest_11);
        // Destination to source copy hence src is a null-terminated empty array
std::cout << "After the copy: " << src << "\n"; 
for (int i = 0; i < 12; ++i) {
if (dest_1[i] == '\0') {
std::cout << "Null termination present..." << "\n";
break;
}
}

// Error cases, the program will not compile for the following cases...
/*char dest_3[0] = {};
_strcpy(dest_3, src);

char dest_4[1] = {};
_strcpy(dest_4, src);*/

return 0;
}

A similar way implemented strcmp as below:




Comments

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

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

Power of Two

  I n this post will be discussing how to calculate if a number is a power of two or not. As an example, 8 is a power of two but the number 10 is not. There are many ways we can solve this. First , we will take an approach which is simple and iterative. In this case, we will calculate the power of two one by one and check with the supplied number. The below code illustrates it. bool isPowerofTwo(unsigned num) { auto y = 1; while (0 != y) { if (num == y) return true; if (num < y) return false; y <<= 1; } return false; } Second , assuming, the number is a 32-bit number, this is also an iterative solution. In this scenario, iterating all bits and counting the set bits. Any number which is a power of 2 will have only one bit set and the rest will be zeros. As an example, 8 in binary representation is 1000. Using this observation, we can implement an iterative solution. bool isPowerofTwo(unsigned num) { auto one_count = 0; for (auto index = 0; index < 32;