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Compiler Warning (level 3) C4197

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'type' : top-level volatile in cast is ignored

The compiler detected a cast to an r-value type which is qualified with volatile, or a cast of an r-value type to some type that is qualified with volatile. According to the C standard (6.5.3), properties associated with qualified types are meaningful only for l-value expressions.

The following sample generates C4197:

// C4197.cpp
// compile with: /W3
#include <stdio.h>
#include <signal.h>
#include <stdlib.h>

void sigproc(int);
struct S
{
   int i;
} s;

int main()
{
   signal(SIGINT, sigproc);
   s.i = 1;
   S *pS = &s;
   for ( ; (volatile int)pS->i ; )   // C4197
      break;
   // for ( ; *(volatile int *)&pS->i ; )   // OK
   //    break;
}

void sigproc(int) // ctrl-C
{
   signal(SIGINT, sigproc);
   s.i = 0;
}