1 | #include <assert.h> |
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2 | int main() { |
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3 | |
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4 | /* |
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5 | The last section established the difference between these four types: |
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6 | */ |
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7 | |
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8 | float a [10] ; // array |
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9 | float (*pa )[10] = & a ; // pointer to array |
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10 | float a0 = a[0] ; // element |
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11 | float *pa0 = &(a[0]); // pointer to element |
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12 | |
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13 | /* |
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14 | But the expression used for obtaining the pointer to the first element is pedantic. |
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15 | The root of all C programmer experience with arrays is the shortcut |
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16 | */ |
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17 | float *pa0x = a ; // (ok) |
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18 | /* |
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19 | which reproduces @pa0@, in type and value: |
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20 | */ |
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21 | assert( pa0 == pa0x ); |
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22 | /* |
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23 | The validity of this initialization is unsettling, in the context of the facts established in the last section. |
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24 | Notably, it initializes name @pa0x@ from expression @a@, when they are not of the same type: |
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25 | */ |
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26 | assert( sizeof(pa0x) != sizeof(a) ); |
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40 | void f( float x[10], float *y ) { |
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41 | static_assert( sizeof(x) == sizeof(void*) ); |
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42 | static_assert( sizeof(y) == sizeof(void*) ); |
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43 | } |
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44 | f(0,0); |
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60 | // reusing local var `float a[10];` |
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61 | float v; |
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62 | f( a, a ); // ok: two decays, one into an array spelling |
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63 | f( &v, &v ); // ok: no decays; a non-array passes to an array spelling |
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80 | char ca[] = "hello"; // array on stack, initialized from read-only data |
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81 | char *cp = "hello"; // pointer to read-only data [decay here] |
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82 | void edit(char c[]) { // param is pointer |
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83 | c[3] = 'p'; |
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84 | } |
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85 | edit(ca); // ok [decay here] |
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86 | edit(cp); // Segmentation fault |
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87 | edit("hello"); // Segmentation fault [decay here] |
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100 | void decay( float x[10] ) { |
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101 | static_assert( sizeof(x) == sizeof(void*) ); |
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102 | } |
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103 | static_assert( sizeof(a) == 10 * sizeof(float) ); |
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104 | decay(a); |
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106 | void no_decay( float (*px)[10] ) { |
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107 | static_assert( sizeof(*px) == 10 * sizeof(float) ); |
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108 | } |
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109 | static_assert( sizeof(*pa) == 10 * sizeof(float) ); |
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110 | no_decay(pa); |
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111 | } |
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