Question

Write a program that inputs a line of text and a search string from the keyboard. Using function strstr, locate the first occurrence of the search string in the line of text, and assign the location to variable searchPtr of type char \(* .\) If the search string is found, print the remainder of the line of text beginning with the search string. Then use strstr again to locate the next occurrence of the search string in the line of text. If a second occurrence is found, print the remainder of the line of text beginning with the second occurrence. [Hint: The second call to strstr should contain the expression searchPtr +1 as its first argument.

Short answer

Read input, use `strstr` to find and print occurrences of the search string.

Step-by-step solution

Set Up the Program

Before writing any code, ensure you have included the necessary header files. For this task, we need `` for input/output operations and `` for using the `strstr` function. Begin by declaring your `main` function.

Get Input from the User

Use `printf` to prompt the user to enter a line of text and a search string. Read these inputs using `fgets` for the line of text to include spaces, and `scanf` for the search string to ensure it's treated as a single word. Make sure to properly handle newline characters that `fgets` might capture.

First Occurrence Search

Use the `strstr` function to search for the first occurrence of the search string within the line of text. Assign the pointer returned by `strstr` to `searchPtr`. This pointer will be `NULL` if the search string is not found.

Print First Search Result

Check if `searchPtr` is not `NULL`. If it's not, use `printf` to print all characters from the position of `searchPtr` to the end of the string. If `searchPtr` is `NULL`, print a message indicating the search string was not found.

Second Occurrence Search

Use `strstr` again, but this time pass `searchPtr + 1` as the first argument. This shifts the search start position to right after the first occurrence, allowing us to find the next occurrence of the search string.

Print Second Search Result

Once again, check if the result of the second `strstr` call is not `NULL`. If it's not, print the remainder of the text from this new position. If `searchPtr` is `NULL`, print a message indicating only one occurrence was found, or none if the first occurrence wasn't found initially.

Finalize the Program

Return 0 from the `main` function to indicate successful execution of the program. Always test your program with various inputs to ensure it handles all edge cases effectively.

Key concepts

strstr function

The `strstr` function in C++ is crucial for finding a substring within another string. This function is part of the C standard library, located within the `` header file. The primary role of `strstr` is to locate the first occurrence of a specified substring, known as the search string, within a larger string, known as the line of text. Here’s how it works: - The function takes two arguments: the pointer to the line of text and the pointer to the search string. - It scans the target string for the search string. - It returns a pointer to the first occurrence of the substring. If the substring is not found, the function returns `NULL`. Using `strstr` is straightforward, but it is essential to check if the return value is `NULL` before attempting to access the data. This check prevents errors, ensuring that any manipulation or output based on the `strstr` result does not cause undefined behavior if the search string is absent.

character pointers

Character pointers in C++ are variables that hold the memory address of a character or the initial character of a string. They are fundamental when dealing with string processing, like using the `strstr` function. Here are some key points about character pointers: - A character pointer, such as `char *searchPtr`, points to a character's memory location, providing access to characters within a string. - When you use `strstr`, it returns a character pointer pointing to the first character of the found substring. - By manipulating this pointer, you can navigate through the string or substrings efficiently. For example, using `searchPtr + 1` allows you to move one character forward in the string, useful for subsequent searches. Working with character pointers requires careful attention, especially with pointer arithmetic, to avoid accessing memory beyond the intended range, which can lead to errors or crashes.

string search in C++

String searching in C++ is a common operation, especially when working with text-based data. Leveraging standard functions like `strstr`, developers can efficiently locate substrings within larger texts. Here’s how to perform a string search in a typical program: 1. **Input Handling:** Prompt the user for both a main string (e.g., a sentence) and a substring (the search string). Use functions like `fgets` to capture the main string with spaces and `scanf` for single-word input. 2. **Initial Search:** Utilize the `strstr` function to find the first occurrence of the search string in the main string. If found, use a character pointer to print from this occurrence to the end of the string.
3. **Subsequent Searches:** To find further occurrences, increment the pointer (e.g., `searchPtr + 1`) and pass it as the starting position for the subsequent `strstr` call.
By handling the pointers returned by `strstr` correctly, you can either find multiple occurrences of the substring in the text, or determine if the search string isn't present, aiding in robust string processing applications.