[英]How do I correctly assign a struct containing an array of int to an array of struct?
I want to know how to assign a struct containing an array of int to an array of structs. 我想知道如何将包含int数组的结构分配给结构数组。 I keep getting the incorrect result no matter what new solution I think of.
无论我想到什么新的解决方案,我都会得到错误的结果。
I believe the problem lies in this piece of code: 我相信问题在于这段代码:
struct Codes *create(int as) {
struct Codes *c = malloc(sizeof (struct Codes)+as * sizeof (int));
c->as = as;
for (int i = 0; i < as; i++) {
c->a[i] = i;
}
return c;
}
The whole code: 整个代码:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
struct Codes {
int as;
int a[];
};
struct Code {
int as;
struct Codes *ci[];
};
struct Codes *create(int as) {
struct Codes *c = malloc(sizeof (struct Codes)+as * sizeof (int));
c->as = as;
for (int i = 0; i < as; i++) {
c->a[i] = i;
}
return c;
}
struct Code *and(int as, struct Codes *cd) {
struct Code *c = malloc(sizeof (struct Code)+as * sizeof (struct Codes));
for (int i = 0; i < as; i++) {
c->ci[i] = cd;
}
c->as = as;
return c;
}
int main(int argc, char **argv) {
struct Codes *cd;
cd = create(4);
struct Code *c;
c = and(2, cd);
for (int i = 0; i < c->as; i += 1) {
for (int j=0; j < c->ci[i]->as; j++) {
printf("%d \n", c->ci[i]->a[j]);
}
}
free(cd);
free(c);
}//main
Actual Result: 实际结果:
0
1
2
3
Expected Result: 预期结果:
0
1
2
3
0
1
2
3
struct Code *c = malloc(sizeof (struct Code)+as * sizeof (struct Codes));
is incorrect. 是不正确的。 The struct Code 's ci is an array of pointers , but you allocated space for an array of structs.
struct Code的ci是一个指针数组,但是你为一个结构数组分配了空间。
To fix this, either change to sizeof(struct Codes *)
, or preferably use the pattern of dereferencing the pointer to the type you're allocating space for: 要解决此问题,请更改为
sizeof(struct Codes *)
,或者最好使用解除引用指向您为其分配空间的类型的指针的模式:
struct Code *c = malloc( sizeof *c + as * sizeof c->ci[0] );
Also, for (int j;
should be for (int j = 0;
. Your code causes undefined behaviour by using uninitialized value of j
, it's just chance that you happened to get the output you did. Using the gcc flag -Wextra
would have diagnosed this error. 另外,
for (int j;
应该是for (int j = 0;
-Wextra
你的代码通过使用未初始化的j
值导致未定义的行为,这恰好是你碰巧得到你输出的结果。使用gcc标志-Wextra
会有诊断出这个错误。
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