QT函数带有外部链接但没有在头文件中声明（QT noreturn属性添加）

Qt noreturn 属性添加

*.cpp:21:1: warning: function ‘f’ could be declared with attribute ‘noreturn’

解决Qt去警告： could be declared with attribute 'noreturn’的方法在函数声明的地方前加
[[noreturn]]
例如：

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//h文件 [[noreturn]] void test(); //cpp文件 void test(){};

　　

原理：

The items between [[ ]] in a function (variable…) declaration are attributes that provide the compiler with extra information about the item they are attached to. The compiler can use these in a range of ways. The “noreturn” attribute has been around since C++ 11.

[[ noreturn ]] attached to a function declaration informs the compiler that control will not return from the function (as in the case of an unconditional throw()). They go in the first declaration of the function. If f() is declared in a header file then this is the place to put it. If the function exists only in a single CPP file, i.e. it is private, with no other declaration then it goes there.

The second code snippet you posted is an example that can lead to undefined behaviour, i.e. returning from a function you explicitly declared would not return control.

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// >>> function.h #ifndef FUNCTION_H #define FUNCTION_H    [[ noreturn ]] void f(); void g();    #endif // FUNCTION_H    // >>> function.cpp #include <iostream> using namespace std;    #include "function.h"    void f() {     cout << "No return" << endl;     throw 1; }    void g() {     cout << "No return" << endl;;     throw 1; }    // >>> main.cpp #include <iostream> using namespace std;    #include "function.h"    [[ noreturn ]] void h() {     cout << "No return" << endl;     throw 3; }    int main(int argc, char **argv) {     cout << "Before f()" << endl;     f();     // this should be unreachable code     cout << "Before g()" << endl;     g();     cout << "Before h()" << endl;     h(); }

　　Functions f() and g() have identical function code but, because the compiler knows that f() will not return, it may generate different code for these function or calls to them. In my experiments with GNU C++ there is no code generated for the calls to g() and h() because they cannot be reached after a call to f().

 

 

 

 

 

 

• The items between [[ ]] in a function (variable…) declaration are attributes that provide the compiler with extra information about the item they are attached to.

函数(变量…)声明中[[]]之间的项是属性，为编译器提供了关于它们附加的项的额外信息。

• The compiler can use these in a range of ways.

编译器可以以多种方式使用这些文件。

• The “noreturn” attribute has been around since C++ 11.

“noreturn”属性从c++ 11开始就存在了。

• [[ noreturn ]] attached to a function declaration informs the compiler that control will not return from the function (as in the case of an unconditional throw()).

附加到函数声明的[[noreturn]]通知编译器控制将不会从函数返回(就像无条件抛出()的情况一样)。

• They go in the first declaration of the function.

它们出现在函数的第一个声明中。

• If f() is declared in a header file then this is the place to put it.

如果f()是在头文件中声明的，那么这里就是放置它的地方。

• If the function exists only in a single CPP file, i.e. it is private, with no other declaration then it goes there.

如果函数只存在于单个CPP文件中，即它是私有的，没有其他声明，那么它就会存在于其中。

• The second code snippet you posted is an example that can lead to undefined behaviour, i.e. returning from a function you explicitly declared would not return control.

你发布的第二个代码片段是一个可能导致未定义行为的例子，例如，从你显式声明的函数返回将不会返回控件。

　　

// >>>

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function.h #ifndef FUNCTION_H #define FUNCTION_H [[ noreturn ]]voidf(); void g(); #endif  // FUNCTION_H// >>> function.cpp #include <iostream> usingnamespace std; #include "function.h" void f() { cout <<"No return"<< endl;throw1;} void g() { cout <<"No return"<< endl;;throw1;}// >>> main.cpp#include <iostream>usingnamespace std;#include "function.h"[[ noreturn ]]voidh(){ cout <<"No return"<< endl;throw3;}intmain(int argc,char**argv){ cout <<"Before f()"<< endl;f();// this should be unreachable code cout <<"Before g()"<< endl;g(); cout <<"Before h()"<< endl;h();}