_Check_return_, C++ (vc++)

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//Microsoft (R) C/C++ Optimizing Compiler Version 19.00.23506 for x64
#include <cstdio>

bool f()                      { return true; };
_Check_return_        bool f__Check_return_()       { return true; };
_Must_inspect_result_ bool f__Must_inspect_result_(){ return true; };

int main(){
    
    // case 0: no implied [[nodiscard]] meaning
    
               f();                               // OK
    bool  b0 = f();                               // OK
    
    // case 1: implicit [[nodiscard]] meaning
    
               fopen("/._1", "r");                // C6031
    FILE* Fp = fopen("/._2", "r");                // OK
    
    // case 2: explicit [[nodiscard]] meaning
    
               f__Check_return_();                // C6031
    bool  b1 = f__Check_return_();                // OK
    
    // case 3: explicit extended meaning:
    //         [[nodiscard]] & must inspect
    
               f__Must_inspect_result_();         // C6031
    bool  b2 = f__Must_inspect_result_();         // C28193
    bool  b3 = f__Must_inspect_result_(); if(b3); // OK
};

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Compilation time: 1,75 sec, absolute running time: 1,16 sec, absolute service time: 2,93 sec