[英]Arrays of pointers that point to arrays of integers
我只是想知道是否有一種方法可以創建一個指針數組,該指針數組指向整數整數數組中每一行的第一列。 例如,請看下面的代碼:
#include <stdio.h>
int day_of_year(int year, int month, int day);
main()
{
printf("Day of year = %d\n", day_of_year(2016, 2, 1));
return 0;
}
static int daytab[2][13] = {
{0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
{0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};
int day_of_year(int year, int month, int day)
{
int leap;
int *nlptr = &daytab[0][0];
int *lpptr = &daytab[1][0];
int *nlend = nlptr + month;
int *lpend = lpptr + month;
leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;
if (leap)
for (; lpptr < lpend; lpptr++)
day += *lpptr;
else
for (; nlptr < nlend; nlptr++)
day += *nlptr;
return day;
}
當我這樣寫時:
int *p[2];
*p[0] = daytab[0][0];
*p[1] = daytab[1][0];
我收到這樣的錯誤:
Error: Array must have at least one element
Error: Variable 'p' is initialized more than once
Error: { expected
Error: Variable 'p' is initialized more than once
Error: { expected
***5 errors in Compile***
我這樣更改它:
int *p[2];
p[0] = &daytab[0][0];
p[1] = &daytab[1][0];
我仍然遇到相同的錯誤。
我知道我們可以像下面這樣創建一個指向字符串的指針數組:
char *str[] = {
"One", "Two", "Three",
"Four", "Five", "Six",
"Seven", "Eight", "Nine"
}
我們如何針對整數數組呢?
您的代碼應具有魅力:
int *p[2];
p[0] = &daytab[0][0];
p[1] = &daytab[1][0];
printf("%d \n", p[0][2]); // shows: 28
printf("%d \n", p[1][2]); // shows: 29
這也適用:
int *p[2] = { &daytab[0][0],&daytab[1][0] };
如果要更改daytab
的定義daytab
類似於第三個示例,則可能需要使用以下代碼:
int * daytab[] = {
(int[]){0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
(int[]){0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}
};
代替。
或使用前哨標記保存並標記數組的結尾,請執行以下操作:
int * daytab[] = {
(int[]){0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
(int[]){0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
NULL
};
或^ 2甚至保留標記也將內部數組結束:
int * daytab[] = {
(int[]){0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, -1},
(int[]){0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, -1},
NULL
};
請注意,此處使用的化合物( (Type){Initialiser}
)僅可從C99開始使用。
如下使用
int *p[2];
p[0] = daytab[0];
p[1] = daytab[1];
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