c——复合类型——数组

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概述

只有一维数组，n(n > 1)维数组本质是一维数组，只不过这个一维数组的数组元素类型为n - 1维数组

数组

一维数组

void one_dim_array(){    int arr[3] = {1, 2, 3};        printf("sizeof(arr) = %ld, sizeof(int[3]) = %ld, sizeof(arr[0]) = %ld\n", sizeof(arr), sizeof(int[3]), sizeof(arr[0]));    printf("&arr = %p, &arr + 1 = %p\n", &arr, &arr + 1);    printf("arr = %p, arr + 1 = %p\n", arr, arr + 1);    printf("&arr[0] = %p, &arr[0] + 1 = %p\n", &arr[0], &arr[0] + 1);    printf("arr[1] = %d, *(arr + 1) = %d\n", arr[1], *(arr + 1));}

output：

sizeof(arr) = 12, sizeof(int[3]) = 12, sizeof(arr[0]) = 4&arr = 0x7fff5fbff810, &arr + 1 = 0x7fff5fbff81carr = 0x7fff5fbff810, arr + 1 = 0x7fff5fbff814&arr[0] = 0x7fff5fbff810, &arr[0] + 1 = 0x7fff5fbff814arr[1] = 2, *(arr + 1) = 2

结论：

数组arr类型为int[3]，数组字长为sizeof(arr) = sizeof(int[3]) = sizeof(int) * 3，&arr类型为int (*)[3]，&arr递增1，值递增sizeof(arr) ，&arr表示数组首地址
数组元素arr[0]类型为int，数组元素字长为sizeof(arr[0]) = sizeof(int)，&arr[0]类型为int *，&arr[0]递增1，值递增sizeof(arr[0])，&arr[0]值为数组首地址
数组arr作为操作数时，隐式转换为int*，即数组元素类型指针，指向数组第一个元素
arr[n]与*(arr + n)等价

多维数组

void multi_dim_array(){    int arr[3][4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};        printf("sizeof(arr) = %ld, sizeof(int[3][4]) = %ld, sizeof(arr[0]) = %ld\n", sizeof(arr), sizeof(int[3][4]), sizeof(arr[0]));    printf("&arr = %p, &arr + 1 = %p\n", &arr, &arr + 1);    printf("arr = %p, arr + 1 = %p\n", arr, arr + 1);    printf("&arr[0] = %p, &arr[0] + 1 = %p\n", &arr[0], &arr[0] + 1);    printf("arr[1] = %p, *(arr + 1) = %p\n", arr[1], *(arr + 1));        printf("sizeof(arr[0]) = %ld, sizeof(int[4]) = %ld, sizeof(arr[0][0]) = %ld\n", sizeof(arr[0]), sizeof(int[4]), sizeof(arr[0][0]));    printf("&arr[0] = %p, &arr[0] + 1 = %p\n", &arr[0], &arr[0] + 1);    printf("arr[0] = %p, arr[0] + 1 = %p\n", arr[0], arr[0] + 1);    printf("&arr[0][0] = %p, &arr[0][0] + 1 = %p\n", &arr[0][0], &arr[0][0] + 1);    printf("arr[0][1] = %d, *(arr[0] + 1) = %d\n", arr[0][1], *(arr[0] + 1));}

output：

sizeof(arr) = 48, sizeof(int[3][4]) = 48, sizeof(arr[0]) = 16&arr = 0x7fff5fbff7e0, &arr + 1 = 0x7fff5fbff810arr = 0x7fff5fbff7e0, arr + 1 = 0x7fff5fbff7f0&arr[0] = 0x7fff5fbff7e0, &arr[0] + 1 = 0x7fff5fbff7f0arr[1] = 0x7fff5fbff7f0, *(arr + 1) = 0x7fff5fbff7f0sizeof(arr[0]) = 16, sizeof(int[4]) = 16, sizeof(arr[0][0]) = 4&arr[0] = 0x7fff5fbff7e0, &arr[0] + 1 = 0x7fff5fbff7f0arr[0] = 0x7fff5fbff7e0, arr[0] + 1 = 0x7fff5fbff7e4&arr[0][0] = 0x7fff5fbff7e0, &arr[0][0] + 1 = 0x7fff5fbff7e4arr[0][1] = 2, *(arr[0] + 1) = 2

结论：

数组arr类型为int[3][4]，数组字长为sizeof(arr) = sizeof(int[3][4]) = sizeof(int[4]) * 3，&arr类型为int (*)[3][4]，&arr递增1，值递增sizeof(arr) ，&arr表示数组首地址
数组元素arr[0]类型为int[4]，数组元素字长为sizeof(arr[0]) = sizeof(int[4])，&arr[0]类型为int (*)[4]，&arr[0]递增1，值递增sizeof(arr[0])，&arr[0]值为数组首地址
数组arr作为操作数时，隐式转换为int (*)[4]，即数组元素类型指针，指向数组第一个元素
arr[n]与*(arr + n)等价

数组参数

数组参数，不管是形参或实参，作为函数操作符操作数，隐式转换数组元素类型指针：

数组作为形参时，形参类型为数组元素类型指针，因此第一维数组长度无意义(可omit，也应该omit，否则易混淆)，大于一维的数组长度不能omit(表示数组元素类型)
数组作为实参时，实参类型为数组元素类型指针，指向数组第一个元素

void feed1(int food[]){    printf("feed1\n");}void feed2(int food[][4]){    printf("feed2\n");}void call_feed(){    int food1[3] = {1, 2, 3};    int food2[3][4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};        feed1(food1);    feed2(food2);}

解释：

feed1形参类型为int*，调用feed1传递实参类型为int*
feed2形参类型为int (*)[4]，调用feed2传递实参类型为int (*)[4]

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