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63 lines
1.7 KiB
Markdown
63 lines
1.7 KiB
Markdown
> 本文档由 [C++那些事网站](https://light-city.github.io/stories_things/cpp-things/assert/) 同步生成，网站版本含多语言与更新排版。
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# C++ assert 断言
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## 关于作者：
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个人公众号：
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## 1.第一个断言案例
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断言，**是宏，而非函数**。
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assert 宏的原型定义在 <assert.h>（C）、<cassert>（C++）中。其作用是如果它的条件返回错误，则终止程序执行。
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可以通过定义 `NDEBUG` 来关闭 assert，**但是需要在源代码的开头，include <assert.h> 之前。**
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```c
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void assert(int expression);
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```
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> 代码样例：[assert.c](https://github.com/Light-City/CPlusPlusThings/tree/master/basic_content/assert/assert.c)
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```c
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#include <stdio.h>
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#include <assert.h>
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int main()
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{
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int x = 7;
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/* Some big code in between and let's say x
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is accidentally changed to 9 */
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x = 9;
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// Programmer assumes x to be 7 in rest of the code
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assert(x==7);
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/* Rest of the code */
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return 0;
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}
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```
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输出：
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```c
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assert: assert.c:13: main: Assertion 'x==7' failed.
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```
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可以看到输出会把源码文件，行号错误位置，提示出来！
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## 2.断言与正常错误处理
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+ 断言主要用于检查逻辑上不可能的情况。
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>例如，它们可用于检查代码在开始运行之前所期望的状态，或者在运行完成后检查状态。与正常的错误处理不同，断言通常在运行时被禁用。
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+ 忽略断言，在代码开头加上：
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```c++
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#define NDEBUG // 加上这行，则 assert 不可用
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```
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> 样例代码：[ignore_assert.c](https://github.com/Light-City/CPlusPlusThings/tree/master/basic_content/assert/ignore_assert.c) |