| 1 | #include <assert.h>
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| 2 | int main() {
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| 3 | float ar[10]; $\C{// array}$
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| 4 | float (*pa)[10] = &ar; $\C{// pointer to array}$
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| 5 | float a0 = ar[0]; $\C{// element}$
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| 6 | float * pa0 = &(ar[0]); $\C{// pointer to element}$
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| 7 |
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| 8 | float * pa0x = ar; $\C{// (ok)}$
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| 9 | assert( pa0 == pa0x );
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| 10 | assert( sizeof(pa0x) != sizeof(ar) );
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| 11 |
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| 12 | void f( float x[10], float * y ) {
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| 13 | static_assert( sizeof(x) == sizeof(void *) );
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| 14 | static_assert( sizeof(y) == sizeof(void *) );
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| 15 | }
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| 16 | f( 0, 0 );
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| 17 |
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| 18 | // reusing local var `float a[10];`}
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| 19 | float v;
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| 20 | f( ar, ar ); $\C{// ok: two decays, one into an array spelling}$
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| 21 | f( &v, &v ); $\C{// ok: no decays; a non-array passes to an array spelling}$
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| 22 |
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| 23 | char ca[] = "hello"; $\C{// array on stack, initialized from read-only data}$
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| 24 | char * cp = "hello"; $\C{// pointer to read-only data [decay here]}$
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| 25 | void edit( char c[] ) { $\C{// parameter is pointer}$
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| 26 | c[3] = 'p';
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| 27 | }
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| 28 | edit( ca ); $\C{// ok [decay here]}$
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| 29 | edit( cp ); $\C{// Segmentation fault}$
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| 30 | edit( "hello" ); $\C{// Segmentation fault [decay here]}$
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| 31 |
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| 32 | void decay( float x[10] ) {
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| 33 | static_assert( sizeof(x) == sizeof(void *) );
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| 34 | }
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| 35 | static_assert( sizeof(ar) == 10 * sizeof(float) );
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| 36 | decay( ar );
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| 37 |
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| 38 | void no_decay( float (*px)[10] ) {
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| 39 | static_assert( sizeof(*px) == 10 * sizeof(float) );
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| 40 | }
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| 41 | static_assert( sizeof(*pa) == 10 * sizeof(float) );
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| 42 | no_decay( pa );
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| 43 | }
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| 44 |
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| 45 | // Local Variables: //
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| 46 | // compile-command: "sed -f sedcmd bkgd-carray-decay.c | gcc-11 -Wall -Wextra -x c -" //
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| 47 | // End: //
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