Geek asks and answers

In this case, does it mean vague selection?

I saw a code sample demonstrating the use of a qualifier volatilein answering a question about the function of C ++ volatile elements given below:

volatile int x;

int DoSomething() {
    x = 1;
    DoSomeOtherStuff();
    return x+1; // Don't just return 2 because we stored a 1 in x.  
                // Check to get its current value
}

I do not know if the qualifier has a volatiledifference in the above code. xis a global variable, and there is a function call between writing and reading on x, and we only read xat a time. Should the compiler do a real read on x(even this is not volatile)?

I think this is different from the following case:

volatile int x;

int DoSomething() {
    x = 1;
    while (x != 1)
        break;
}

In this case, we re-read ximmediately after writing to x, so volatileit is necessary to get the updated value xwritten by other threads.

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}

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DoSomeOtherStuff(). :

static int DoSomeOtherStuff()
{
    return 42;
}

volatile int x;

int DoSomething() {
  x = 1;
  DoSomeOtherStuff();
  return x+1; // Don't just return 2 because we stored a 1 in x.
  // Check to get its current value
}

GCC -O3 DoSomeOtherStuff() ( ), x, x+1 .

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SO : volatile?

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  Accessing the memory-mapped peripherals register.

  Sharing the global variables or buffers between the multiple threads.

  Accessing the global variables in an interrupt routine or signal handler.

This link is also useful: http://aticleworld.com/understanding-volatile-qualifier-in-c/

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