雙維度選項卡數

Question

我忘了怎麼算的雙重維度Ç陣列，因爲我不明白爲什麼這個代碼返回我12的計數，而不是6

// My tab 
static NSString *kStringTag[][2] = { 
    {@"string1", @"1"}, 
    {@"string2", @"1"}, 
    {@"string3", @"0"}, 
    {@"string4", @"0"}, 
    {@"string5", @"1"}, 
    {@"string6", @"1"}, 
    {nil, nil} 
}; 

// My C func 
unsigned int tablen(void **tab) 
{ 
    unsigned int i = 0; 

    while (tab[i] != nil) 
     i++; 

    return i; 
} 

- (void)viewDidLoad 
{ 
    NSLog(@"%d", tablen((void **)kStringTab)); 
} 

Answer 1

您的代碼不是C.

如果它是C，tab將指針數組的數組NSString的（無論是）。

在C中，指向NSString的指針數組不一定與指向void的指針兼容...所以刪除了這些類型並獲取類型正確的。

在C，這個工程......

#include <stdio.h> 

static char *kStringTab[][2] = { 
    {"string1", "1"}, 
    {"string2", "1"}, 
    {"string3", "0"}, 
    {"string4", "0"}, 
    {"string5", "1"}, 
    {"string6", "1"}, 
    {NULL, NULL}, 
}; 

unsigned int tablen(char *tab[][2]) { 
    unsigned int i = 0; 
    while (tab[i][0] != NULL) i++; 
    return i; 
} 

int main(void) { 
    printf("%d\n", tablen(kStringTab)); 
    return 0; 
} 

建議：增加你的編譯器和記警告的警戒線。

---

編輯：新的通用版本

#include <math.h> 
#include <stdio.h> 

static double anothertest[][3] = { 
    {42, 54, -122}, 
    {33, -0.001, 0.001}, 
    {6, 0, 7},    /* 0 in middle: stop condition in nullp2 :) */ 
    {2, 2, 2}, 
}; 

static char *kStringTab[][2] = { 
    {"string1", "1"}, 
    {"string2", "1"}, 
    {"string3", "0"}, 
    {"string4", "0"}, 
    {"string5", "1"}, 
    {"string6", "1"}, 
    {NULL, NULL}, 
}; 

int nullp2(const void *elem) { 
    const double *tmp = elem; 
    return (fabs(tmp[1]) < 0.000000001); 
} 

int nullp(const void *elem) { 
    char (*const *tmp)[2] = elem; /* tmp is a pointer to each element of kStringTab */ 
    return ((*tmp)[0] == NULL); 
} 

unsigned int tablen(void *x, size_t size, 
        int (*check)(const void *)) { 
    char *y = x; 
    unsigned int i = 0; 

    while (!check(y)) { 

    i++; 
    y += size; 
    } 
    return i; 
} 

int main(void) { 
    printf("tablen returns %d\n", 
     tablen(kStringTab, sizeof *kStringTab, nullp)); 
    printf("tablen returns %d\n", 
     tablen(anothertest, sizeof *anothertest, nullp2)); 
    return 0; 
} 

你可以看到它running at ideone。

Answer 2

tab[i] 

是隻是從內存地址的偏移量，並且您有12個項目存儲在該地址。