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工欲善其事必先利其器，优雅的代码离不开静态代码检查工具，大家可能平时使用较多的是cppcheck，但今天我想跟大家分享另一个静态代码检查工具clang-tidy。
不同于cppcheck使用正则表达式进行静态代码分析，clang-tidy是基于语法分析树的静态代码检查工具，虽然它的速度比正则表达式慢一些，但是它检查的更准确、全面，而且不仅可以做静态检查，还可以做一些修复工作，自行添加一些自定义检查规则。
话不多说，上代码：
- #include <iostream>
- int main() {
- int a = 1.2;
- return 0;
- }
这里有隐式类型转换，可以使用clang-tidy来检测：
- ~/test$ clang-tidy -checks=* test_lint.cpp --
- 7748 warnings generated.
- /home/wangzhiqiang/test/test_lint.cpp:20:13: warning: implicit conversion from 'double' to 'int' changes value from 1.2 to 1 [clang-diagnostic-literal-conversion]
- int a = 1.2;
- ^
- Suppressed 7747 warnings (7747 in non-user code).
- Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
这里也许你有疑问了，这不就是一个普通的编译警告嘛，正常使用编译器也可以检查出来，那再看一段代码：
- #include <iostream>
- int main() {
- char* d = NULL;
- return 0;
- }
我们都知道在C++中应该更多的使用nullptr而不是NULL，这里使用了NULL而不是使用nullptr，可能我们在开发过程中没有注意到这种用法，所以clang-tidy派上了用场：
- ~/test$ clang-tidy -checks=* test_lint.cpp --
- 7748 warnings generated.
- /home/wangzhiqiang/test/test_lint.cpp:20:15: warning: use nullptr [modernize-use-nullptr]
- char* d = NULL;
- ^~~~~
- nullptr
- Suppressed 7747 warnings (7747 in non-user code).
- Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
再举一个例子：
- struct Base {
- virtual void func() {
- }
- };
- struct Derive : Base {
- virtual void func() {
- }
- };
这里可能我们乍一看没有任何问题，其实在C++11里派生类继承父类，重写了某些函数时最好加上override关键字，通过clang-tidy还是可以检测出来：
- ~/test$ clang-tidy -checks=* test_lint.cpp --
- 7749 warnings generated.
- /home/wangzhiqiang/test/test_lint.cpp:14:18: warning: prefer using 'override' or (rarely) 'final' instead of 'virtual' [hicpp-use-override]
- virtual void func() {
- ~~~~~~~~~~~~~^
- override
- Suppressed 7747 warnings (7747 in non-user code).
- Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well.
该工具还可以检查代码是否符合编码规范，例如Google编码规范等，看这段头文件相关代码：
- #include <iostream>
- #include <string>
- #include <memory>
这里其实有一点点问题，头文件引用顺序不满足编码规范，这里其实clang-format都可以检测出来，但clang-tidy也可以检测出来，通过-fix还可以进行自动修复：
- ~/test$ clang-tidy -checks=* test_lint.cpp --
- 8961 warnings generated.
- /home/wangzhiqiang/test/test_lint.cpp:2:1: warning: #includes are not sorted properly [llvm-include-order]
- #include <string>
- ^ ~~~~~~~~
- Suppressed 8960 warnings (8960 in non-user code).
- Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well
它还可以检测隐藏的内存泄漏：
- int main() {
- char* ct = (char*)malloc(323);
- return 0;
- }
这是使用clang-tidy的检测结果：
- ~/test$ clang-tidy -checks=* test_lint.cpp --
- 7756 warnings generated.
- /home/wangzhiqiang/test/test_lint.cpp:20:5: warning: initializing non-owner 'char *' with a newly created 'gsl::owner<>' [cppcoreguidelines-owning-memory]
- char* ct = (char*)malloc(323);
- ^
- /home/wangzhiqiang/test/test_lint.cpp:20:5: warning: use auto when initializing with a cast to avoid duplicating the type name [hicpp-use-auto]
- char* ct = (char*)malloc(323);
- ^~~~~
- auto
- /home/wangzhiqiang/test/test_lint.cpp:20:11: warning: Value stored to 'ct' during its initialization is never read [clang-analyzer-deadcode.DeadStores]
- char* ct = (char*)malloc(323);
- ^
- /home/wangzhiqiang/test/test_lint.cpp:20:11: note: Value stored to 'ct' during its initialization is never read
- /home/wangzhiqiang/test/test_lint.cpp:20:16: warning: C-style casts are discouraged; use static_cast [google-readability-casting]
- char* ct = (char*)malloc(323);
- ^~~~~~~~~~~~~ ~
- static_cast<char*>( )
- /home/wangzhiqiang/test/test_lint.cpp:20:16: warning: do not use C-style cast to convert between unrelated types [cppcoreguidelines-pro-type-cstyle-cast]
- /home/wangzhiqiang/test/test_lint.cpp:20:23: warning: do not manage memory manually; consider a container or a smart pointer [cppcoreguidelines-no-malloc]
- char* ct = (char*)malloc(323);
- ^
- /home/wangzhiqiang/test/test_lint.cpp:21:5: warning: Potential leak of memory pointed to by 'ct' [clang-analyzer-unix.Malloc]
- return 0;
- ^
- /home/wangzhiqiang/test/test_lint.cpp:20:23: note: Memory is allocated
- char* ct = (char*)malloc(323);
- ^
- /home/wangzhiqiang/test/test_lint.cpp:21:5: note: Potential leak of memory pointed to by 'ct'
- return 0;
- ^
- Suppressed 7747 warnings (7747 in non-user code).
- Use -header-filter=.* to display errors from all non-system headers. Use -system-headers to display errors from system headers as well
clang-tidy还有很多高端功能，大概可以检测出250种问题，大体主要分为几大类：
- abseil：检测abseil库的相关问题
- android：检测Android相关问题
- boost：检测boost库的相关问题
- cert：检测CERT的代码规范
- cpp-core-guidelines：检测是否违反cpp-core-guidelines
- google：检测是否违反google编码规范
- llvm：检测是否违反llvm编码规范
- performance：检测性能相关的问题
- readability：检测与可读性相关，但又不属于某些编码规范的问题
- modernize：检测是否使用现代C++11相关的代码问题
而且适用于Windows/Linux/MacOS多平台，还支持命令行，CLion/VSCode/VSStudio插件等，检测规则还可以定制，重要的是免费开源，快去用起来吧，写出优雅的C++代码~
参考资料：
https://clang.llvm.org/extra/clang-tidy/
https://www.bilibili.com/video/av96166240/
