String search technology in C++

In C, string search technology is a very important skill because it is one of the necessary skills in handling string operations. C provides a variety of built-in functions and algorithms to help us with string search. These functions and algorithms provide a general set of skills that can be used in many different situations.

This article will introduce several commonly used C string search techniques, as well as their advantages, disadvantages and usage scenarios.

1. String search function

C String search function is one of the most commonly used search techniques. These functions are designed to find the target string in a string. or characters. The following are several commonly used string search functions in C:

• find()

find() function can be used to find a substring in a string. A string or character and returns the position of its first occurrence. If not found, std::string::npos is returned. For example, the following code will find the substring "hello" in the string s:

std::string s = "hello world";
size_t pos = s.find("hello");
if (pos != std::string::npos) {
    // found
}

• rfind()

The rfind() function is similar to the find() function, But it starts searching from the right and returns the last occurrence. For example, the following code will find the last occurrence of the character 'e' in the string s:

std::string s = "hello world";
size_t pos = s.rfind('e');
if (pos != std::string::npos) {
    // found
}

• find_first_of()

find_first_of() function is used to find The position of the first occurrence of one of the given characters in a string. For example, the following code will find the first occurrence of a vowel in the string s:

std::string s = "hello world";
size_t pos = s.find_first_of("aeiou");
if (pos != std::string::npos) {
    // found
}

• find_last_of()

find_last_of() function and find_first_of() The function is the same, but looks from right to left. For example, the following code will find the last occurrence of a vowel in the string s:

std::string s = "hello world";
size_t pos = s.find_last_of("aeiou");
if (pos != std::string::npos) {
    // found
}

These functions are the most commonly used string finding techniques in C. They are very flexible and can be used in strings. Find various types of substrings and characters. Their disadvantage is that once the first match is found, the search stops and the location is returned, which may not be the result you are looking for.

2. String search algorithm

C STL provides some very powerful algorithms that can be used to find target strings or characters in strings. These algorithms are designed to be general-purpose and can handle many types of data structures. The following are several commonly used C string search algorithms:

• std::search()

The search() function can be used in the range of two iterators Finds a subsequence and returns an iterator over the first subsequence. For example, the following code will find the substring "world" in the string s:

std::string s = "hello world";
std::string sub = "world";
auto it = std::search(s.begin(), s.end(), sub.begin(), sub.end());
if (it != s.end()) {
    // found
}

• std::find()

The find() function can be used in Finds an element within an iterator range and returns an iterator of the element. For example, the following code will find the position of the character 'e' in the string s:

std::string s = "hello world";
auto it = std::find(s.begin(), s.end(), 'e');
if (it != s.end()) {
    // found
}

• std::find_first_of()

find_first_of() function is the same as previously introduced Like the string function, it is used to find the first element in an iterator range that matches one of the given characters and returns an iterator of elements. For example, the following code will find the first vowel in the string s:

std::string s = "hello world";
auto it = std::find_first_of(s.begin(), s.end(), "aeiou");
if (it != s.end()) {
    // found
}

These algorithms are general and scalable and can be used in many different data structures and scenarios. Their disadvantage is that they can be slower than the direct lookup techniques of string functions because they require additional iterator operations to find the target string or character.

3. Regular Expressions

The C standard library also provides a regular expression library, which can be used to find substrings that match specific patterns in strings. Regular expressions can be used to find more complex patterns, for example it can help us find text in a specific format such as mobile phone numbers, email addresses, etc. Here is an example of using a regular expression library to find a simple pattern:

std::string s = "The quick brown fox jumps over the lazy dog";
std::regex reg("fox.*lazy");
if (std::regex_search(s, reg)) {
    // found
}

Regular expressions are a powerful and flexible technique that can help us process and find various types of text data. But these advantages also bring some disadvantages. Regular expression syntax is complex and may be slower than other search techniques introduced earlier.

Summary

In C programming, string search technology is an important area. This article introduces several common string search techniques, including string search functions, string search algorithms, and regular expressions. These technical drawbacks vary, but they can all be used in a variety of different data structures and scenarios. As a programmer, you need to choose the tool that works best for you to perform string lookups with the fastest speed and accuracy.

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