如何寫出優(yōu)雅的C++代碼
# 干了這碗雞湯
不要否定自己的未來，未來會很晴朗，好運也在路上。
工欲善其事必先利其器，優(yōu)雅的代碼離不開靜態(tài)代碼檢查工具，大家可能平時使用較多的是cppcheck，但今天我想跟大家分享另一個靜態(tài)代碼檢查工具clang-tidy。
不同于cppcheck使用正則表達式進行靜態(tài)代碼分析，clang-tidy是基于語法分析樹的靜態(tài)代碼檢查工具，雖然它的速度比正則表達式慢一些，但是它檢查的更準確、全面，而且不僅可以做靜態(tài)檢查，還可以做一些修復工作，自行添加一些自定義檢查規(guī)則。
話不多說，上代碼：
int main() {int a = 1.2;return 0;}
這里有隱式類型轉換，可以使用clang-tidy來檢測：
~/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.
這里也許你有疑問了，這不就是一個普通的編譯警告嘛，正常使用編譯器也可以檢查出來，那再看一段代碼：
int main() {char* d = NULL;return 0;}
我們都知道在C++中應該更多的使用nullptr而不是NULL，這里使用了NULL而不是使用nullptr，可能我們在開發(fā)過程中沒有注意到這種用法，所以clang-tidy派上了用場：
~/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;^~~~~nullptrSuppressed 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.
再舉一個例子：
struct Base {virtual void func() {}};struct Derive : Base {virtual void func() {}};
這里可能我們乍一看沒有任何問題，其實在C++11里派生類繼承父類，重寫了某些函數(shù)時最好加上override關鍵字，通過clang-tidy還是可以檢測出來：
~/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() {~~~~~~~~~~~~~^overrideSuppressed 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.
該工具還可以檢查代碼是否符合編碼規(guī)范，例如Google編碼規(guī)范等，看這段頭文件相關代碼：
這里其實有一點點問題，頭文件引用順序不滿足編碼規(guī)范，這里其實clang-format都可以檢測出來，但clang-tidy也可以檢測出來，通過-fix還可以進行自動修復：
~/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
它還可以檢測隱藏的內存泄漏：
int main() {char* ct = (char*)malloc(323);return 0;}
這是使用clang-tidy的檢測結果：
~/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 allocatedchar* 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還有很多高端功能，大概可以檢測出250種問題，大體主要分為幾大類：
abseil：檢測abseil庫的相關問題 android：檢測Android相關問題 boost：檢測boost庫的相關問題 cert：檢測CERT的代碼規(guī)范 cpp-core-guidelines：檢測是否違反cpp-core-guidelines google：檢測是否違反google編碼規(guī)范 llvm：檢測是否違反llvm編碼規(guī)范 performance：檢測性能相關的問題 readability：檢測與可讀性相關，但又不屬于某些編碼規(guī)范的問題 modernize：檢測是否使用現(xiàn)代C++11相關的代碼問題
而且適用于Windows/Linux/MacOS多平臺，還支持命令行，CLion/VSCode/VSStudio插件等，檢測規(guī)則還可以定制，重要的是免費開源，快去用起來吧，寫出優(yōu)雅的C++代碼~
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