[7972603] | 1 | #include <assert.h> |
---|
| 2 | int main() { |
---|
[266732e] | 3 | float a[10]; $\C{// array}$ |
---|
| 4 | float (*pa)[10] = &a; $\C{// pointer to array}$ |
---|
| 5 | float a0 = a[0]; $\C{// element}$ |
---|
| 6 | float *pa0 = &(a[0]); $\C{// pointer to element}$ |
---|
| 7 | |
---|
| 8 | float *pa0x = a; $\C{// (ok)}$ |
---|
| 9 | assert( pa0 == pa0x ); |
---|
| 10 | assert( sizeof(pa0x) != sizeof(a) ); |
---|
| 11 | |
---|
| 12 | void f( float x[10], float *y ) { |
---|
| 13 | static_assert( sizeof(x) == sizeof(void*) ); |
---|
| 14 | static_assert( sizeof(y) == sizeof(void*) ); |
---|
| 15 | } |
---|
| 16 | f(0,0); |
---|
| 17 | |
---|
| 18 | // reusing local var `float a[10];`} |
---|
| 19 | float v; |
---|
| 20 | f( a, a ); $\C{// ok: two decays, one into an array spelling}$ |
---|
| 21 | f( &v, &v ); $\C{// ok: no decays; a non-array passes to an array spelling}$ |
---|
| 22 | |
---|
| 23 | char ca[] = "hello"; $\C{// array on stack, initialized from read-only data}$ |
---|
| 24 | char *cp = "hello"; $\C{// pointer to read-only data [decay here]}$ |
---|
| 25 | void edit(char c[]) { $\C{// param is pointer}$ |
---|
| 26 | c[3] = 'p'; |
---|
| 27 | } |
---|
| 28 | edit(ca); $\C{// ok [decay here]}$ |
---|
| 29 | edit(cp); $\C{// Segmentation fault}$ |
---|
| 30 | edit("hello"); $\C{// Segmentation fault [decay here]}$ |
---|
| 31 | |
---|
| 32 | void decay( float x[10] ) { |
---|
| 33 | static_assert( sizeof(x) == sizeof(void*) ); |
---|
| 34 | } |
---|
| 35 | static_assert( sizeof(a) == 10 * sizeof(float) ); |
---|
| 36 | decay(a); |
---|
| 37 | |
---|
| 38 | void no_decay( float (*px)[10] ) { |
---|
| 39 | static_assert( sizeof(*px) == 10 * sizeof(float) ); |
---|
| 40 | } |
---|
| 41 | static_assert( sizeof(*pa) == 10 * sizeof(float) ); |
---|
| 42 | no_decay(pa); |
---|
[7972603] | 43 | } |
---|
[266732e] | 44 | |
---|
| 45 | // Local Variables: // |
---|
| 46 | // compile-command: "sed -f sedcmd bkgd-carray-decay.c > tmp.c; gcc tmp.c" // |
---|
| 47 | // End: // |
---|