编辑“︁C++ 字符串搜索”︁（章节）

== 搜索函数详解 ==

=== `find()`函数 ===

`find()`函数用于在主字符串中查找子字符串或字符的第一次出现。其基本语法如下：

<syntaxhighlight lang="cpp">
size_t find(const std::string& str, size_t pos = 0) const;
size_t find(const char* s, size_t pos = 0) const;
size_t find(char c, size_t pos = 0) const;
</syntaxhighlight>

其中：
- `str`或`s`是要查找的子字符串。
- `c`是要查找的字符。
- `pos`是开始搜索的位置（默认为0）。

如果找到子字符串或字符，则返回其起始位置（索引）；否则返回`std::string::npos`。

==== 示例 ====

<syntaxhighlight lang="cpp">
#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, world! Welcome to C++ programming.";
    std::string substr = "world";

    // 查找子字符串
    size_t found = str.find(substr);
    if (found != std::string::npos) {
        std::cout << "Substring found at position: " << found << std::endl;
    } else {
        std::cout << "Substring not found." << std::endl;
    }

    // 查找字符
    found = str.find('W');
    if (found != std::string::npos) {
        std::cout << "Character found at position: " << found << std::endl;
    } else {
        std::cout << "Character not found." << std::endl;
    }

    return 0;
}
</syntaxhighlight>

输出：
<pre>
Substring found at position: 7
Character found at position: 14
</pre>

=== `rfind()`函数 ===

`rfind()`函数与`find()`类似，但它从字符串的末尾开始搜索，返回子字符串或字符的最后一次出现的位置。

==== 示例 ====

<syntaxhighlight lang="cpp">
#include <iostream>
#include <string>

int main() {
    std::string str = "C++ is fun. C++ is powerful.";
    std::string substr = "C++";

    size_t found = str.rfind(substr);
    if (found != std::string::npos) {
        std::cout << "Last occurrence found at position: " << found << std::endl;
    } else {
        std::cout << "Substring not found." << std::endl;
    }

    return 0;
}
</syntaxhighlight>

输出：
<pre>
Last occurrence found at position: 13
</pre>

=== 其他搜索函数 ===

- `find_first_of()`：查找字符集合中任意字符的第一次出现。
- `find_last_of()`：查找字符集合中任意字符的最后一次出现。
- `find_first_not_of()`：查找不在字符集合中的第一个字符。
- `find_last_not_of()`：查找不在字符集合中的最后一个字符。

==== 示例 ====

<syntaxhighlight lang="cpp">
#include <iostream>
#include <string>

int main() {
    std::string str = "C++ programming is fun!";
    std::string vowels = "aeiouAEIOU";

    // 查找第一个元音字母
    size_t found = str.find_first_of(vowels);
    if (found != std::string::npos) {
        std::cout << "First vowel found at position: " << found << std::endl;
    }

    // 查找第一个非字母字符
    found = str.find_first_not_of("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ");
    if (found != std::string::npos) {
        std::cout << "First non-alphabetic character found at position: " << found << std::endl;
    }

    return 0;
}
</syntaxhighlight>

输出：
<pre>
First vowel found at position: 1
First non-alphabetic character found at position: 3
</pre>