Question

Write two versions of each string copy and string-concatenation function in Fig. 8.30. The first version should use array subscripting, and the second should use pointers and pointer arithmetic.

Short answer

String copy and concatenation can be done using both array subscripting and pointers.

Step-by-step solution

Understanding the Problem

We need to write string manipulation functions using two methods: array subscripting and pointer arithmetic. The two main functions are string copy and string concatenation.

Implementing String Copy with Array Subscripting

The first version of the string copy function uses array subscripting. Define a function `str_copy_subscript(char dest[], const char src[])` where a loop iterates over the `src` array, copying each element into `dest` using a subscript.

Implementing String Copy with Pointers

The second version uses pointers. Define `str_copy_pointer(char *dest, const char *src)`. Using a loop, increment both `src` and `dest` pointers while copying the value from `src` to `dest` until the null character is encountered.

Implementing String Concatenation with Array Subscripting

The first version of string concatenation uses array subscripting. Define `str_concat_subscript(char dest[], const char src[])`, where you first find the end of `dest` using a loop, then append each element from `src`.

Implementing String Concatenation with Pointers

The second version uses pointer arithmetic. Define `str_concat_pointer(char *dest, const char *src)`. Move the `dest` pointer to the end of the current string, then use a loop to copy each element from `src` to `dest`, incrementing the pointers accordingly.

Key concepts

String Manipulation

String manipulation in C++ involves working with sequences of characters to perform tasks like copying, concatenating, or modifying strings. Strings in C++ can be treated as arrays of characters, where each character can be accessed independently. This makes string manipulation a fundamental aspect of programming in C++. Common string manipulation tasks include:

• Copying: Duplicating the contents of one string into another.
• Concatenating: Joining two strings together to form a new string.

Understanding how to manage and manipulate strings effectively is crucial, as it forms the basis for handling text data in applications. For instance, copying a string might seem trivial, but in C++, it's important to know the differences between using array subscripting versus pointers for these operations.

Array Subscripting

Array subscripting is a method of accessing elements within a collection by specifying an index. In C++, arrays are zero-based, meaning the first element is accessed using index 0.
To perform operations like string copy or concatenation using array subscripting, consider the following:

• Access elements directly by using their indexed position.
• Use loops to traverse the array, enabling you to copy elements one-by-one.

When copying a string using array subscripting, you'd typically iterate through each character in the source array and assign it to the corresponding index in the destination array. This method is straightforward but requires careful index management to avoid going out of bounds.

Pointer Arithmetic

Pointer arithmetic involves manipulating the memory address that a pointer holds to traverse through the data it points to. In C++, pointers can be incremented, decremented, or manipulated to directly interact with the memory locations of elements.
When applied to strings, pointer arithmetic allows for:

• Efficient Traversal: You can move through a string by incrementing the pointer.
• Direct Memory Access: Allows manipulation at the byte level, which can be more efficient than subscripting.

For string copy and concatenation, using a pointer involves setting the initial pointer to the start of the string and moving it as each character is accessed or modified. It can be more efficient as it skips the overhead of index calculation. However, programmers should handle pointers with care to prevent memory errors.

Function Implementation

Function implementation in C++ refers to writing the code that defines the behavior of functions. Functions encapsulate specific tasks or operations, providing a way to organize and reuse code efficiently. When implementing string manipulation functions such as copy or concatenate, developers need to consider:

• Function Signature: Define the input parameters and the return type.
• Error Handling: Ensure the function handles edge cases, such as null pointers or empty strings.
• Performance: Consider the efficiency of the implementation, choosing the best method (array subscripting or pointer arithmetic) based on the needs of the task.

In implementing these functions using C++, being mindful of how strings are passed and altered is important. Whether to use array subscripting or pointer arithmetic depends on the specific use case and the programmer's comfort level with each approach.