[英]Getting -Wincompatible-pointer-types for struct pointer warning when compiling
I'm following along with this tutorial to learn about external chaining in Hashtables in C.我正在跟随本教程学习 C 中哈希表中的外部链接。 I find that I get the following error when compiling with gcc --std=c99
:我发现使用gcc --std=c99
编译时出现以下错误:
warning: assignment to "person *" {aka 'struct <anonymous> *'} from incompatible pointer type 'struct person *' [-Wincompatible-pointer-types]
101 | tmp = tmp->next;
warning: assignment to "person *" {aka 'struct <anonymous> *'} from incompatible pointer type 'struct person *' [-Wincompatible-pointer-types]
112 | p->next = hash_table[index];
warning: assignment to "person *" {aka 'struct <anonymous> *'} from incompatible pointer type 'struct person *' [-Wincompatible-pointer-types]
121 | tmp = tmp->next;
warning: assignment to "person *" {aka 'struct <anonymous> *'} from incompatible pointer type 'struct person *' [-Wincompatible-pointer-types]
132 | tmp = tmp->next;
warning: assignment to "person *" {aka 'struct <anonymous> *'} from incompatible pointer type 'struct person *' [-Wincompatible-pointer-types]
136 | hash_table[index] = tmp->nxt;
I find that this occurs only with the next
pointer for the person struct:我发现这只发生在 person 结构的next
指针中:
typedef struct {
char name[TABLE_SIZE];
int age;
//...
struct person *next;
} person;
For functions like these:对于这样的功能:
void print_table(){
for (int i=0; i < TABLE_SIZE; i++0 {
if (hash_table[i] == NULL) {
printf("\t%i\t---n\n",i);
}
else {
printf("\t%i\t",i);
person *tmp = hash_table[i];
while (tmp != NULL) {
printf("%s -", tmp->name);
tmp = tmp->next;
}
printf("\n");
}
}
}
bool hash_table_insert(person *p) {
if (p == NULL) return false;
int index = hash(p->name);
p->next = hash_table[index];
hash_table[index] = p;
return true;
}
The hashtable's output is correct so clearly it works fine but it gets these warnings.哈希表的 output 是正确的,所以很明显它工作正常,但它会收到这些警告。 I did not get these warnings until implementing the chaining technique.在实施链接技术之前,我没有收到这些警告。 I'm inclined to believe it has something to do with the addition of struct person *next;
我倾向于相信这与添加struct person *next;
有关系。 , or at least it's usage. ,或者至少是它的用法。 Any ideas?有任何想法吗?
This typedef declaration这个 typedef 声明
typedef struct {
char name[TABLE_SIZE];
int age;
//...
struct person *next;
} person;
declares an unnamed structure with the typedef name person
, and this record within the unnamed structure使用 typedef 名称person
声明一个未命名结构,并且该记录位于未命名结构中
struct person *next;
introduces an incomplete type specifier struct person
.引入了一个不完整的类型说明符struct person
。
Thus person
and struct person
are two different type specifiers.因此person
和struct person
是两个不同的类型说明符。
You could, for example例如,您可以
typedef struct person person;
struct person {
char name[TABLE_SIZE];
int age;
//...
struct person *next;
};
or或者
typedef struct person {
char name[TABLE_SIZE];
int age;
//...
struct person *next;
} person;
An anonymous struct is a struct without a tag .匿名结构是没有标签的结构。 Give your struct a tag and then use struct person
everywhere.给你的结构一个标签,然后在任何地方使用struct person
。
And don't bother with typedefs for structs.并且不要为结构体的 typedefs 烦恼。 All they do is save you from typing struct
in a few places, like declarations.他们所做的只是让你不用在几个地方输入struct
,比如声明。
struct person {
char name[TABLE_SIZE];
int age;
//...
struct person *next;
};
...
struct person *tmp = hash_table[i];
On another note, functions taking no arguments should be declared with a (void)
argument list, otherwise they indicate an unspecified but fixed argument list.另一方面,不采用 arguments 的函数应该用(void)
参数列表声明,否则它们表示未指定但固定的参数列表。 In particular, in C, something like特别是,在 C 中,类似
int foo();
is not a prototype!不是原型! It's an old-style (K&R C) function declaration from the age when C did not have the void
keyword.这是 C 没有void
关键字时的旧式 (K&R C) function 声明。
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