constptr.cpp

来自「开放源码的编译器open watcom 1.6.0版的源代码」· C++ 代码 · 共 58 行

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// 'int **' cannot be converted to 'const int **'
// this is not allowed because it would allow a constant value to
// be changed which the C/C++ type system is supposed to prevent
// (this example is from the ISO/ANSI C++ draft section 8.2.1)
// see CNSTPTR2.CPP for a simpler example
#include <stdio.h>

const int ci = 10;
const int *pc = &ci;
const int **ppc;
int *p;

void main()
{
    ppc = &p;           // suppose WATCOM C++ allowed this to work...
                        // 'int **' -> 'const int **'
    *ppc = &ci;         // OK
                        // 'const int *' -> 'const int *'
    *p = 5;             // OK (but we just changed 'ci' to 5)
                        // problem is the first assignment in 'main'
                        // is incorrect

    // Borland C++ prints 'ci is now 5 (should be 10)'
    printf( "ci is now %d (should be 10)\n", *pc );
}