> For the complete documentation index, see [llms.txt](https://docs.1l.lol/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.1l.lol/strings/string-functions.md).

# 字符串函数

### 常用字符串函数（C 风格，需 ）

| 函数             | 作用            |
| -------------- | ------------- |
| `strlen(s)`    | 求长度（不含 \0）    |
| `strcpy(a, b)` | 把 b 复制到 a     |
| `strcat(a, b)` | 把 b 拼接到 a 后   |
| `strcmp(a, b)` | 比较，相等返回 0     |
| `strstr(a, b)` | 查找子串，返回首次出现位置 |
| `strrev`(非标准)  | 反转字符串         |

### 大小写转换

```cpp
#include <cctype>
char c = 'a';
toupper(c);  // 转大写
tolower(c);  // 转小写
isalpha(c);  // 是否字母
isdigit(c);  // 是否数字
```

### 查找、分割、替换

```cpp
string s = "Hello World";
int p = s.find("World");          // 查找，返回下标 6
string sub = s.substr(0, 5);      // 截取，从 0 开始取 5 个
s.replace(6, 5, "GESP");          // 从下标 6 起 5 个字符替换为 "GESP"

// 分割
string t = "a,b,c";
int start = 0;
for (int i = 0; i <= t.size(); i++) {
    if (i == t.size() || t[i] == ',') {
        cout << t.substr(start, i - start) << endl;
        start = i + 1;
    }
}
```

### C++ string 常用操作

```cpp
string a = "abc", b = "def";
cout << a + b;        // 拼接 abcdef
cout << a.size();     // 长度
a.push_back('z');     // 追加字符
```


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