3月 2021

关于typedef指针类型后的非主流const行为(misc-misplaced-const)

这是一个之前没怎么注意过的细节问题,首先,参加如下代码:

struct MyStruct
{
    int type;
    char name[40];
};

typedef MyStruct * PMyStruct;

int main(int argc, char * argv[])
{
    MyStruct my1{0}, my2{0};
    const MyStruct * pmy1 = &my1;
    pmy1 = &my2;
    const PMyStruct pmy2 = &my1;
    pmy2 = &my2;
}

很简单的一段代码,但是全引出了一个不寻常的问题:此段代码编译时,第二个pmy2结构体指针会导致编译器(gcc)报错:“error: assignment of read-only variable ‘pmy2’”,此时如果配合有clang-tidy之类的代码扫描工具,会发现pmy2声明赋值位置提示:“Clang-Tidy: ‘pmy2’ declared with a const-qualified typedef; results in the type being ‘MyStruct *const’ instead of ‘const MyStruct *’”(clang-tidy的misc-misplaced-const)!

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