| 1 | #include <assert.h> |
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| 2 | int main() { |
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| 3 | float a[10]; $\C{// array}$ |
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| 4 | float (*pa)[10] = &a; $\C{// pointer to array}$ |
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| 5 | float a0 = a[0]; $\C{// element}$ |
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| 6 | float *pa0 = &(a[0]); $\C{// pointer to element}$ |
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| 7 | |
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| 8 | float *pa0x = a; $\C{// (ok)}$ |
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| 9 | assert( pa0 == pa0x ); |
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| 10 | assert( sizeof(pa0x) != sizeof(a) ); |
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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( a, a ); $\C{// ok: two decays, one into an array spelling}$ |
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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[]) { $\C{// param is pointer}$ |
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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(a) == 10 * sizeof(float) ); |
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| 36 | decay(a); |
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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 > tmp.c; gcc tmp.c" // |
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| 47 | // End: // |
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