[英]Reallocating array inside struct
typedef struct {
int count;
int *items;
}set;
set* set_alloc(set *src, int num);
int set_insert(set *s, int num);
int main() {
set *A = NULL;
A = set_alloc(A, 0);
A = set_alloc(A, 1); //this and line below is part of inserting function
A->items[0] = 2;
system("pause");
}
set* set_alloc(set *src, int num) {
if (src == NULL && num == 0) {
set *src = (set*)malloc(sizeof(set));
src->count = 0;
src->items = NULL;
}
else {
src->count = num;
src->items = (int*)realloc(src->items, num*sizeof(int));
}
return src;
}
Code above is able to allocate memory for the array of items inside the set and for the set itself, however, it fails to realloc that array of items.. I could set it a constant size, but I don't really wanna go around this problem because I've had it in previous projects. 上面的代码能够为集合内部的项目数组和集合本身分配内存,但是,它无法重新分配该项目数组..我可以将它设置为常量,但我真的不想四处走动这个问题,因为我在之前的项目中已经有了它。
Here: 这里:
set *src = (set*)malloc(sizeof(set));
you are redeclaring src
(in a block scope), you want: 你要重新声明
src
(在块范围内),你想要:
src = malloc(sizeof(set));
I could set it a constant size, but I don't really wanna go around this problem because I've had it in previous projects.
我可以设置一个恒定的大小,但我真的不想解决这个问题,因为我已经在之前的项目中使用过它。
An alternative to realloc
when you don't know the size beforehand is a linked list. 当您事先不知道大小时,
realloc
的替代方法是链接列表。
Your function never returns the newly allocated "*src" from function set_alloc, see my comments below, please use the same *src for allocation, and your code should work. 你的函数永远不会从函数set_alloc返回新分配的“* src”,请参阅下面的评论,请使用相同的* src进行分配,你的代码应该可行。
set* set_alloc(set *src, int num) {
if (src == NULL && num == 0) {
set *src = (set*)malloc(sizeof(set)); ***//<--- This pointer is local to if block.***
*//Please Correct code as =>* src = (set*)malloc(sizeof(set));
src->count = 0;
src->items = NULL;
}
else {
src->count = num;
src->items = (int*)realloc(src->items, num*sizeof(int));
}
return src; ***// <-- This is returning the in parameter not the malloced pointer ***
}
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