> 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/bigint.md).

# 字符串比较（strcmp）

### C 风格：strcmp

```cpp
#include <cstring>
int strcmp(const char *a, const char *b);
```

按**字典序**逐字符比较：

| 返回值 | 含义     |
| --- | ------ |
| 0   | a == b |
| 正数  | a > b  |
| 负数  | a < b  |

```cpp
char a[] = "apple", b[] = "banana";
if (strcmp(a, b) < 0) cout << "a 在前";   // 成立
if (strcmp(a, a) == 0) cout << "相等";
```

返回的正/负数通常是首个不同字符的 ASCII 差值，不要依赖具体数值，只判断正负或是否为 0。

### C++ string：直接用运算符

```cpp
string a = "apple", b = "banana";
if (a < b)  cout << "a 在前";
if (a == b) cout << "相等";
if (a != b) cout << "不同";
```

`string` 重载了 `< > ==` 等，也按字典序比较，比 `strcmp` 更直观，推荐使用。

### 字典序规则

从第一个字符开始逐一比较 ASCII 值，直到出现不同或结束；一个串是另一个的前缀时，**短的更小**。例如 `"app" < "apple"`。


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