问题描述
这是我的代码。尝试malloc被malloc的元素，不知道怎么释放。
char *d = "apple";
int main() {
char *a = malloc(10 * sizeof(char));
char **b = &a;
strcpy(a,d);
printf("%c",*b[0]);
b[0] = malloc(3 * sizeof(char));
free(b[0]);
free(a);
}
解决方法
之后
A = [[1,2,3,4,5,6,7,8,9,0],[2,1],[3,1,2],[4,3],[5,4],[6,5]]
A = np.array(A)
height = 3
width = 4
overlap = 1
y_step = height-overlap
x_step = width-overlap
B = [A[y:y+height,x:x+width] for y in range(0,A.shape[0],y_step) for x in range(0,A.shape[1],x_step)]
/**
* Define the behavior of the component here.
* Keep on data on the state.
*/
const onClick = (index: number) => {
// Update a field in an object in a list _without mutating_ the objects.
setActiveDays([
...activeDays.slice(0,index),{ ...activeDays[index],active: !activeDays[index].active },...activeDays.slice(index + 1),]);
};
// Then
{activeDays.map((day: any,i: number) => (
<DaySelector
key={day.key}
day={day.day}
active={day.active}
onClick={() => onClick(i)}
/>
))}
与 char **b = &a;
相同。所以当你这样做
b[0]您正在用这个新分配替换 a 的值。
那么 b[0] = malloc(3 * sizeof(char));
与 a 相同。因此，如果您同时执行这两项操作，那么您将释放相同的内存两次，这是一次双重释放。
您还泄露了分配给 free(b[0]) 的原始分配，因为您不再拥有指向该分配的指针。您需要另一个变量来保存它，以便您可以释放它。
free(a);